How to set the MAC address for Docker LXC containers?

How to set the MAC address for Docker LXC containers? - docker

Whenever I run a docker container, I see that it uses a random MAC address:
eth0 Link encap:Ethernet HWaddr de:6f:de:74:bd:d9
How do I set a specific MAC address for a container run?
Will I be able to have multiple containers running simultaneously with the same MAC address? These containers do not need to access the outside network and do not need to talk to each other.

Newer versions of docker take a --mac-address=12:34:56:78:9a:bc switch to docker run.
root#kevin-VirtualBox:~# sudo docker run --rm --mac-address"=12:34:de:b0:6b:61" ubuntu ifconfig | grep HWaddr
eth0 Link encap:Ethernet HWaddr 12:34:de:b0:6b:61
See https://docs.docker.com/reference/run/

The MAC address is set using the LXC configuration option lxc.network.hwaddr.
Here is an example of how to set MAC address using Docker 0.6.1:
docker run --lxc-conf="lxc.network.hwaddr=92:20:de:b0:6b:61" my_image ifconfig
In the output, you will see the HWaddr that was set:
eth0 Link encap:Ethernet HWaddr 92:20:de:b0:6b:61
Update:
The previous switch -lxc-conf (with 1 dash) has been deprecated.
To use the above switch, you docker must be using the LXC driver: -e lxc

The above answer worked for me and helped me very much, but I needed a little more detail to get it to work.
This is very helpful when you have an app that licenses of the mac-address.
As this was the only post I could find on this topic, I thought I expand on it.
For me, it required a little more to work - else the switch will be silently discarded.
For ubuntu 12.04:
edit /etc/default/docker: DOCKER_OPTS="--dns 8.8.8.8 -e lxc"
apt-get install lxc (lxc-docker is not enough)
docker run --lxc-conf="lxc.network.hwaddr=92:20:de:b0:6b:61" -t myimage

Related

How to link external url to docker image [duplicate]

I have a Nginx running inside a docker container. I have a MySql running on the host system. I want to connect to the MySql from within my container. MySql is only binding to the localhost device.
Is there any way to connect to this MySql or any other program on localhost from within this docker container?
This question is different from "How to get the IP address of the docker host from inside a docker container" due to the fact that the IP address of the docker host could be the public IP or the private IP in the network which may or may not be reachable from within the docker container (I mean public IP if hosted at AWS or something). Even if you have the IP address of the docker host it does not mean you can connect to docker host from within the container given that IP address as your Docker network may be overlay, host, bridge, macvlan, none etc which restricts the reachability of that IP address.

Edit:
If you are using Docker-for-mac or Docker-for-Windows 18.03+, connect to your mysql service using the host host.docker.internal (instead of the 127.0.0.1 in your connection string).
If you are using Docker-for-Linux 20.10.0+, you can also use the host host.docker.internal if you started your Docker container with the --add-host host.docker.internal:host-gateway option.
Otherwise, read below
TLDR
Use --network="host" in your docker run command, then 127.0.0.1 in your docker container will point to your docker host.
Note: This mode only works on Docker for Linux, per the documentation.
Note on docker container networking modes
Docker offers different networking modes when running containers. Depending on the mode you choose you would connect to your MySQL database running on the docker host differently.
docker run --network="bridge" (default)
Docker creates a bridge named docker0 by default. Both the docker host and the docker containers have an IP address on that bridge.
on the Docker host, type sudo ip addr show docker0 you will have an output looking like:
[vagrant#docker:~] $ sudo ip addr show docker0
4: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 56:84:7a:fe:97:99 brd ff:ff:ff:ff:ff:ff
inet 172.17.42.1/16 scope global docker0
valid_lft forever preferred_lft forever
inet6 fe80::5484:7aff:fefe:9799/64 scope link
valid_lft forever preferred_lft forever
So here my docker host has the IP address 172.17.42.1 on the docker0 network interface.
Now start a new container and get a shell on it: docker run --rm -it ubuntu:trusty bash and within the container type ip addr show eth0 to discover how its main network interface is set up:
root#e77f6a1b3740:/# ip addr show eth0
863: eth0: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 66:32:13:f0:f1:e3 brd ff:ff:ff:ff:ff:ff
inet 172.17.1.192/16 scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::6432:13ff:fef0:f1e3/64 scope link
valid_lft forever preferred_lft forever
Here my container has the IP address 172.17.1.192. Now look at the routing table:
root#e77f6a1b3740:/# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 172.17.42.1 0.0.0.0 UG 0 0 0 eth0
172.17.0.0 * 255.255.0.0 U 0 0 0 eth0
So the IP Address of the docker host 172.17.42.1 is set as the default route and is accessible from your container.
root#e77f6a1b3740:/# ping 172.17.42.1
PING 172.17.42.1 (172.17.42.1) 56(84) bytes of data.
64 bytes from 172.17.42.1: icmp_seq=1 ttl=64 time=0.070 ms
64 bytes from 172.17.42.1: icmp_seq=2 ttl=64 time=0.201 ms
64 bytes from 172.17.42.1: icmp_seq=3 ttl=64 time=0.116 ms
docker run --network="host"
Alternatively you can run a docker container with network settings set to host. Such a container will share the network stack with the docker host and from the container point of view, localhost (or 127.0.0.1) will refer to the docker host.
Be aware that any port opened in your docker container would be opened on the docker host. And this without requiring the -p or -P docker run option.
IP config on my docker host:
[vagrant#docker:~] $ ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:98:dc:aa brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe98:dcaa/64 scope link
valid_lft forever preferred_lft forever
and from a docker container in host mode:
[vagrant#docker:~] $ docker run --rm -it --network=host ubuntu:trusty ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:98:dc:aa brd ff:ff:ff:ff:ff:ff
inet 10.0.2.15/24 brd 10.0.2.255 scope global eth0
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe98:dcaa/64 scope link
valid_lft forever preferred_lft forever
As you can see both the docker host and docker container share the exact same network interface and as such have the same IP address.
Connecting to MySQL from containers
bridge mode
To access MySQL running on the docker host from containers in bridge mode, you need to make sure the MySQL service is listening for connections on the 172.17.42.1 IP address.
To do so, make sure you have either bind-address = 172.17.42.1 or bind-address = 0.0.0.0 in your MySQL config file (my.cnf).
If you need to set an environment variable with the IP address of the gateway, you can run the following code in a container :
export DOCKER_HOST_IP=$(route -n | awk '/UG[ \t]/{print $2}')
then in your application, use the DOCKER_HOST_IP environment variable to open the connection to MySQL.
Note: if you use bind-address = 0.0.0.0 your MySQL server will listen for connections on all network interfaces. That means your MySQL server could be reached from the Internet ; make sure to set up firewall rules accordingly.
Note 2: if you use bind-address = 172.17.42.1 your MySQL server won't listen for connections made to 127.0.0.1. Processes running on the docker host that would want to connect to MySQL would have to use the 172.17.42.1 IP address.
host mode
To access MySQL running on the docker host from containers in host mode, you can keep bind-address = 127.0.0.1 in your MySQL configuration and connect to 127.0.0.1 from your containers:
[vagrant#docker:~] $ docker run --rm -it --network=host mysql mysql -h 127.0.0.1 -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 36
Server version: 5.5.41-0ubuntu0.14.04.1 (Ubuntu)
Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
note: Do use mysql -h 127.0.0.1 and not mysql -h localhost; otherwise the MySQL client would try to connect using a unix socket.

For all platforms
Docker v 20.10 and above (since December 14th 2020)
Use your internal IP address or connect to the special DNS name host.docker.internal which will resolve to the internal IP address used by the host.
On Linux, using the Docker command, add --add-host=host.docker.internal:host-gateway to your Docker command to enable this feature.
To enable this in Docker Compose on Linux, add the following lines to the container definition:
extra_hosts:
- "host.docker.internal:host-gateway"
For older macOS and Windows versions of Docker
Docker v 18.03 and above (since March 21st 2018)
Use your internal IP address or connect to the special DNS name host.docker.internal which will resolve to the internal IP address used by the host.
Linux support pending https://github.com/docker/for-linux/issues/264
For older macOS versions of Docker
Docker for Mac v 17.12 to v 18.02
Same as above but use docker.for.mac.host.internal instead.
Docker for Mac v 17.06 to v 17.11
Same as above but use docker.for.mac.localhost instead.
Docker for Mac 17.05 and below
To access host machine from the docker container you must attach an IP alias to your network interface. You can bind whichever IP you want, just make sure you're not using it to anything else.
sudo ifconfig lo0 alias 123.123.123.123/24
Then make sure that you server is listening to the IP mentioned above or 0.0.0.0. If it's listening on localhost 127.0.0.1 it will not accept the connection.
Then just point your docker container to this IP and you can access the host machine!
To test you can run something like curl -X GET 123.123.123.123:3000 inside the container.
The alias will reset on every reboot so create a start-up script if necessary.
Solution and more documentation here: https://docs.docker.com/docker-for-mac/networking/#use-cases-and-workarounds

Use
host.docker.internal
instead of
localhost

I doing a hack similar to above posts of get the local IP to map to a alias name (DNS) in the container. The major problem is to get dynamically with a simple script that works both in Linux and OSX the host IP address. I did this script that works in both environments (even in Linux distribution with "$LANG" != "en_*" configured):
ifconfig | grep -E "([0-9]{1,3}\.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1
So, using Docker Compose, the full configuration will be:
Startup script (docker-run.sh):
export DOCKERHOST=$(ifconfig | grep -E "([0-9]{1,3}\.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1)
docker-compose -f docker-compose.yml up
docker-compose.yml:
myapp:
build: .
ports:
- "80:80"
extra_hosts:
- "dockerhost:$DOCKERHOST"
Then change http://localhost to http://dockerhost in your code.
For a more advance guide of how to customize the DOCKERHOST script, take a look at this post with a explanation of how it works.

Solution for Linux (kernel >=3.6).
Ok, your localhost server has a default docker interface docker0 with IP address 172.17.0.1. Your container started with default network settings --net="bridge".
Enable route_localnet for docker0 interface:
$ sysctl -w net.ipv4.conf.docker0.route_localnet=1
Add these rules to iptables:
$ iptables -t nat -I PREROUTING -i docker0 -d 172.17.0.1 -p tcp --dport 3306 -j DNAT --to 127.0.0.1:3306
$ iptables -t filter -I INPUT -i docker0 -d 127.0.0.1 -p tcp --dport 3306 -j ACCEPT
Create MySQL user with access from '%' that means - from anyone, excluding localhost:
CREATE USER 'user'#'%' IDENTIFIED BY 'password';
Change in your script the mysql-server address to 172.17.0.1.
From the kernel documentation:
route_localnet - BOOLEAN: Do not consider loopback addresses as martian source or destination while routing. This enables the use of 127/8 for local routing purposes (default FALSE).

This worked for me on an NGINX/PHP-FPM stack without touching any code or networking where the app's just expecting to be able to connect to localhost
Mount mysqld.sock from the host to inside the container.
Find the location of the mysql.sock file on the host running mysql:
netstat -ln | awk '/mysql(.*)?\.sock/ { print $9 }'
Mount that file to where it's expected in the docker:
docker run -v /hostpath/to/mysqld.sock:/containerpath/to/mysqld.sock
Possible locations of mysqld.sock:
/tmp/mysqld.sock
/var/run/mysqld/mysqld.sock
/var/lib/mysql/mysql.sock
/Applications/MAMP/tmp/mysql/mysql.sock # if running via MAMP

Until host.docker.internal is working for every platform, you can use my container acting as a NAT gateway without any manual setup:
https://github.com/qoomon/docker-host

Simplest solution for Mac OSX
Just use the IP address of your Mac. On the Mac run this to get the IP address and use it from within the container:
ifconfig | grep 'inet 192'| awk '{ print $2}'
As long as the server running locally on your Mac or in another docker container is listening to 0.0.0.0, the docker container will be able to reach out at that address.
If you just want to access another docker container that is listening on 0.0.0.0 you can use 172.17.0.1

Very simple and quick, check your host IP with ifconfig (linux) or ipconfig (windows) and then create a docker-compose.yml:
version: '3' # specify docker-compose version
services:
nginx:
build: ./ # specify the directory of the Dockerfile
ports:
- "8080:80" # specify port mapping
extra_hosts:
- "dockerhost:<yourIP>"
This way, your container will be able to access your host. When accessing your DB, remember to use the name you specified before, in this case dockerhost and the port of your host in which the DB is running.

Several solutions come to mind:
Move your dependencies into containers first
Make your other services externally accessible and connect to them with that external IP
Run your containers without network isolation
Avoid connecting over the network, use a socket that is mounted as a volume instead
The reason this doesn't work out of the box is that containers run with their own network namespace by default. That means localhost (or 127.0.0.1 pointing to the loopback interface) is unique per container. Connecting to this will connect to the container itself, and not services running outside of docker or inside of a different docker container.
Option 1: If your dependency can be moved into a container, I would do this first. It makes your application stack portable as others try to run your container on their own environment. And you can still publish the port on your host where other services that have not been migrated can still reach it. You can even publish the port to the localhost interface on your docker host to avoid it being externally accessible with a syntax like: -p 127.0.0.1:3306:3306 for the published port.
Option 2: There are a variety of ways to detect the host IP address from inside of the container, but each have a limited number of scenarios where they work (e.g. requiring Docker for Mac). The most portable option is to inject your host IP into the container with something like an environment variable or configuration file, e.g.:
docker run --rm -e "HOST_IP=$(ip route get 1 | sed -n 's/^.*src $[0-9.]*$ .*$/\1/p')" ...
This does require that your service is listening on that external interface, which could be a security concern. For other methods to get the host IP address from inside of the container, see this post.
Slightly less portable is to use host.docker.internal. This works in current versions of Docker for Windows and Docker for Mac. And in 20.10, the capability has been added to Docker for Linux when you pass a special host entry with:
docker run --add-host host.docker.internal:host-gateway ...
The host-gateway is a special value added in Docker 20.10 that automatically expands to a host IP. For more details see this PR.
Option 3: Running without network isolation, i.e. running with --net host, means your application is running on the host network namespace. This is less isolation for the container, and it means you cannot access other containers over a shared docker network with DNS (instead, you need to use published ports to access other containerized applications). But for applications that need to access other services on the host that are only listening on 127.0.0.1 on the host, this can be the easiest option.
Option 4: Various services also allow access over a filesystem based socket. This socket can be mounted into the container as a bind mounted volume, allowing you to access the host service without going over the network. For access to the docker engine, you often see examples of mounting /var/run/docker.sock into the container (giving that container root access to the host). With mysql, you can try something like -v /var/run/mysqld/mysqld.sock:/var/run/mysqld/mysql.sock and then connect to localhost which mysql converts to using the socket.

Solution for Windows 10
Docker Community Edition 17.06.0-ce-win18 2017-06-28 (stable)
You can use DNS name of the host docker.for.win.localhost, to resolve to the internal IP. (Warning some sources mentioned windows but it should be win)
Overview
I needed to do something similar, that is connect from my Docker container to my localhost, which was running the Azure Storage Emulator and CosmosDB Emulator.
The Azure Storage Emulator by default listens on 127.0.0.1, while you can change the IP its bound too, I was looking for a solution that would work with default settings.
This also works for connecting from my Docker container to SQL Server and IIS, both running locally on my host with default port settings.

For windows,
I have changed the database url in spring configuration: spring.datasource.url=jdbc:postgresql://host.docker.internal:5432/apidb
Then build the image and run. It worked for me.

None of the answers worked for me when using Docker Toolbox on Windows 10 Home, but 10.0.2.2 did, since it uses VirtualBox which exposes the host to the VM on this address.

This is not an answer to the actual question. This is how I solved a similar problem. The solution comes totally from: Define Docker Container Networking so Containers can Communicate. Thanks to Nic Raboy
Leaving this here for others who might want to do REST calls between one container and another. Answers the question: what to use in place of localhost in a docker environment?
Get how your network looks like docker network ls
Create a new network docker network create -d my-net
Start the first container docker run -d -p 5000:5000 --network="my-net" --name "first_container" <MyImage1:v0.1>
Check out network settings for first container docker inspect first_container. "Networks": should have 'my-net'
Start the second container docker run -d -p 6000:6000 --network="my-net" --name "second_container" <MyImage2:v0.1>
Check out network settings for second container docker inspect second_container. "Networks": should have 'my-net'
ssh into your second container docker exec -it second_container sh or docker exec -it second_container bash.
Inside of the second container, you can ping the first container by ping first_container. Also, your code calls such as http://localhost:5000 can be replaced by http://first_container:5000

If you're running with --net=host, localhost should work fine. If you're using default networking, use the static IP 172.17.0.1.
See this - https://stackoverflow.com/a/48547074/14120621

For those on Windows, assuming you're using the bridge network driver, you'll want to specifically bind MySQL to the IP address of the hyper-v network interface.
This is done via the configuration file under the normally hidden C:\ProgramData\MySQL folder.
Binding to 0.0.0.0 will not work. The address needed is shown in the docker configuration as well, and in my case was 10.0.75.1.

Edit: I ended up prototyping out the concept on GitHub. Check out: https://github.com/sivabudh/system-in-a-box
First, my answer is geared towards 2 groups of people: those who use a Mac, and those who use Linux.
The host network mode doesn't work on a Mac. You have to use an IP alias, see: https://stackoverflow.com/a/43541681/2713729
What is a host network mode? See: https://docs.docker.com/engine/reference/run/#/network-settings
Secondly, for those of you who are using Linux (my direct experience was with Ubuntu 14.04 LTS and I'm upgrading to 16.04 LTS in production soon), yes, you can make the service running inside a Docker container connect to localhost services running on the Docker host (eg. your laptop).
How?
The key is when you run the Docker container, you have to run it with the host mode. The command looks like this:
docker run --network="host" -id <Docker image ID>
When you do an ifconfig (you will need to apt-get install net-tools your container for ifconfig to be callable) inside your container, you will see that the network interfaces are the same as the one on Docker host (eg. your laptop).
It's important to note that I'm a Mac user, but I run Ubuntu under Parallels, so using a Mac is not a disadvantage. ;-)
And this is how you connect NGINX container to the MySQL running on a localhost.

For Linux, where you cannot change the interface the localhost service binds to
There are two problems we need to solve
Getting the IP of the host
Making our localhost service available to Docker
The first problem can be solved using qoomon's docker-host image, as given by other answers.
You will need to add this container to the same bridge network as your other container so that you can access it. Open a terminal inside your container and ensure that you can ping dockerhost.
bash-5.0# ping dockerhost
PING dockerhost (172.20.0.2): 56 data bytes
64 bytes from 172.20.0.2: seq=0 ttl=64 time=0.523 ms
Now, the harder problem, making the service accessible to docker.
We can use telnet to check if we can access a port on the host (you may need to install this).
The problem is that our container will only be able to access services that bind to all interfaces, such as SSH:
bash-5.0# telnet dockerhost 22
SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3
But services bound only to localhost will be inaccessible:
bash-5.0# telnet dockerhost 1025
telnet: can't connect to remote host (172.20.0.2): Connection refused
The proper solution here would be to bind the service to dockers bridge network. However, this answer assumes that it is not possible for you to change this. So we will instead use iptables.
First, we need to find the name of the bridge network that docker is using with ifconfig. If you are using an unnamed bridge, this will just be docker0. However, if you are using a named network you will have a bridge starting with br- that docker will be using instead. Mine is br-5cd80298d6f4.
Once we have the name of this bridge, we need to allow routing from this bridge to localhost. This is disabled by default for security reasons:
sysctl -w net.ipv4.conf.<bridge_name>.route_localnet=1
Now to set up our iptables rule. Since our container can only access ports on the docker bridge network, we are going to pretend that our service is actually bound to a port on this network.
To do this, we will forward all requests to <docker_bridge>:port to localhost:port
iptables -t nat -A PREROUTING -p tcp -i <docker_bridge_name> --dport <service_port> -j DNAT --to-destination 127.0.0.1:<service_port>
For example, for my service on port 1025
iptables -t nat -A PREROUTING -p tcp -i br-5cd80298d6f4 --dport 1025 -j DNAT --to-destination 127.0.0.1:1025
You should now be able to access your service from the container:
bash-5.0# telnet dockerhost 1025
220 127.0.0.1 ESMTP Service Ready

First see this answer for the options that you have to fix this problem. But if you use docker-compose you can add network_mode: host to your service and then use 127.0.0.1 to connect to the local host. This is just one of the options described in the answer above. Below you can find how I modified docker-compose.yml from https://github.com/geerlingguy/php-apache-container.git:
---
version: "3"
services:
php-apache:
+ network_mode: host
image: geerlingguy/php-apache:latest
container_name: php-apache
...
+ indicates the line I added.
[Additional info] This has also worked in version 2.2. and "host" or just 'host' are both worked in docker-compose.
---
version: "2.2"
services:
php-apache:
+ network_mode: "host"
or
+ network_mode: host
...

I disagree with the answer from Thomasleveil.
Making mysql bind to 172.17.42.1 will prevent other programs using the database on the host to reach it. This will only work if all your database users are dockerized.
Making mysql bind to 0.0.0.0 will open the db to outside world, which is not only a very bad thing to do, but also contrary to what the original question author wants to do. He explicitly says "The MySql is running on localhost and not exposing a port to the outside world, so its bound on localhost"
To answer the comment from ivant
"Why not bind mysql to docker0 as well?"
This is not possible. The mysql/mariadb documentation explicitly says it is not possible to bind to several interfaces. You can only bind to 0, 1, or all interfaces.
As a conclusion, I have NOT found any way to reach the (localhost only) database on the host from a docker container. That definitely seems like a very very common pattern, but I don't know how to do it.

Try this:
version: '3.5'
services:
yourservice-here:
container_name: container_name
ports:
- "4000:4000"
extra_hosts: # <---- here
- localhost:192.168.1.202
- or-vitualhost.local:192.168.1.202
To get 192.168.1.202, uses ifconfig
This worked for me. Hope this help!

In 7 years the question was asked, it is either docker has changed, or no one tried this way. So I will include my own answer.
I have found all answers use complex methods. Today, I have needed this, and found 2 very simple ways:
use ipconfig or ifconfig on your host and make note of all IP addresses. At least two of them can be used by the container.
I have a fixed local network address on WiFi LAN Adapter: 192.168.1.101. This could be 10.0.1.101. the result will change depending on your router
I use WSL on windows, and it has its own vEthernet address: 172.19.192.1
use host.docker.internal. Most answers have this or another form of it depending on OS. The name suggests it is now globally used by docker.
A third option is to use WAN address of the machine, or in other words IP given by the service provider. However, this may not work if IP is not static, and requires routing and firewall settings.

You need to know the gateway! My solution with local server was to expose it under 0.0.0.0:8000, then run docker with subnet and run container like:
docker network create --subnet=172.35.0.0/16 --gateway 172.35.0.1 SUBNET35
docker run -d -p 4444:4444 --net SUBNET35 <container-you-want-run-place-here>
So, now you can access your loopback through http://172.35.0.1:8000

Connect to the gateway address.
❯ docker network inspect bridge | grep Gateway
"Gateway": "172.17.0.1"
Make sure the process on the host is listening on this interface or on all interfaces and is started after docker. If using systemd, you can add the below to make sure it is started after docker.
[Unit]
After=docker.service
Example
❯ python -m http.server &> /dev/null &
[1] 149976
❯ docker run --rm python python -c "from urllib.request import urlopen;print(b'Directory listing for' in urlopen('http://172.17.0.1:8000').read())"
True

Here is my solution : it works for my case
set local mysql server to public access by comment
#bind-address = 127.0.0.1
in /etc/mysql/mysql.conf.d
restart mysql server
sudo /etc/init.d/mysql restart
run the following command to open user root access any host
mysql -uroot -proot
GRANT ALL PRIVILEGES ON *.* TO 'root'#'%' IDENTIFIED BY 'root' WITH
GRANT OPTION;
FLUSH PRIVILEGES;
create sh script : run_docker.sh
#!bin/bash
HOSTIP=`ip -4 addr show scope global dev eth0 | grep inet | awk '{print \$2}' | cut -d / -f 1`
docker run -it -d --name web-app \
--add-host=local:${HOSTIP} \
-p 8080:8080 \
-e DATABASE_HOST=${HOSTIP} \
-e DATABASE_PORT=3306 \
-e DATABASE_NAME=demo \
-e DATABASE_USER=root \
-e DATABASE_PASSWORD=root \
sopheamak/springboot_docker_mysql
run with docker-composer
version: '2.1'
services:
tomcatwar:
extra_hosts:
- "local:10.1.2.232"
image: sopheamak/springboot_docker_mysql
ports:
- 8080:8080
environment:
- DATABASE_HOST=local
- DATABASE_USER=root
- DATABASE_PASSWORD=root
- DATABASE_NAME=demo
- DATABASE_PORT=3306

You can get the host ip using alpine image
docker run --rm alpine ip route | awk 'NR==1 {print $3}'
This would be more consistent as you're always using alpine to run the command.
Similar to Mariano's answer you can use same command to set an environment variable
DOCKER_HOST=$(docker run --rm alpine ip route | awk 'NR==1 {print $3}') docker-compose up

you can use net alias for your machine
OSX
sudo ifconfig lo0 alias 123.123.123.123/24 up
LINUX
sudo ifconfig lo:0 123.123.123.123 up
then from the container you can see the machine by 123.123.123.123

The CGroups and Namespaces are playing major role in the Container Ecosystem.
Namespace provide a layer of isolation. Each container runs in a separate namespace and its access is limited to that namespace. The Cgroups controls the resource utilization of each container, whereas Namespace controls what a process can see and access the respective resource.
Here is the basic understanding of the solution approach you could follow,
Use Network Namespace
When a container spawns out of image, a network interface is defined and create. This gives the container unique IP address and interface.
$ docker run -it alpine ifconfig
By changing the namespace to host, cotainers networks does not remain isolated to its interface, the process will have access to host machines network interface.
$ docker run -it --net=host alpine ifconfig
If the process listens on ports, they'll be listened on the host interface and mapped to the container.
Use PID Namespace
By changing the Pid namespace allows a container to interact with other process beyond its normal scope.
This container will run in its own namespace.
$ docker run -it alpine ps aux
By changing the namespace to the host, the container can also see all the other processes running on the system.
$ docker run -it --pid=host alpine ps aux
Sharing Namespace
This is a bad practice to do this in production because you are breaking out of the container security model which might open up for vulnerabilities, and easy access to eavesdropper. This is only for debugging tools and understating the loopholes in container security.
The first container is nginx server. This will create a new network and process namespace. This container will bind itself to port 80 of newly created network interface.
$ docker run -d --name http nginx:alpine
Another container can now reuse this namespace,
$ docker run --net=container:http mohan08p/curl curl -s localhost
Also, this container can see the interface with the processes in a shared container.
$ docker run --pid=container:http alpine ps aux
This will allow you give more privileges to containers without changing or restarting the application. In the similar way you can connect to mysql on host, run and debug your application. But, its not recommend to go by this way. Hope it helps.

Until fix is not merged into master branch, to get host IP just run from inside of the container:
ip -4 route list match 0/0 | cut -d' ' -f3
(as suggested by #Mahoney here).

I solved it by creating a user in MySQL for the container's ip:
$ sudo mysql<br>
mysql> create user 'username'#'172.17.0.2' identified by 'password';<br>
Query OK, 0 rows affected (0.00 sec)
mysql> grant all privileges on database_name.* to 'username'#'172.17.0.2' with grant option;<br>
Query OK, 0 rows affected (0.00 sec)
$ sudo vim /etc/mysql/mysql.conf.d/mysqld.cnf
<br>bind-address = 172.17.0.1
$ sudo systemctl restart mysql.service
Then on container: jdbc:mysql://<b>172.17.0.1</b>:3306/database_name

How to access a webservice outside of the docker image [duplicate]

I have a Nginx running inside a docker container. I have a MySql running on the host system. I want to connect to the MySql from within my container. MySql is only binding to the localhost device.
Is there any way to connect to this MySql or any other program on localhost from within this docker container?
This question is different from "How to get the IP address of the docker host from inside a docker container" due to the fact that the IP address of the docker host could be the public IP or the private IP in the network which may or may not be reachable from within the docker container (I mean public IP if hosted at AWS or something). Even if you have the IP address of the docker host it does not mean you can connect to docker host from within the container given that IP address as your Docker network may be overlay, host, bridge, macvlan, none etc which restricts the reachability of that IP address.

Use
host.docker.internal
instead of
localhost

I doing a hack similar to above posts of get the local IP to map to a alias name (DNS) in the container. The major problem is to get dynamically with a simple script that works both in Linux and OSX the host IP address. I did this script that works in both environments (even in Linux distribution with "$LANG" != "en_*" configured):
ifconfig | grep -E "([0-9]{1,3}\.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1
So, using Docker Compose, the full configuration will be:
Startup script (docker-run.sh):
export DOCKERHOST=$(ifconfig | grep -E "([0-9]{1,3}\.){3}[0-9]{1,3}" | grep -v 127.0.0.1 | awk '{ print $2 }' | cut -f2 -d: | head -n1)
docker-compose -f docker-compose.yml up
docker-compose.yml:
myapp:
build: .
ports:
- "80:80"
extra_hosts:
- "dockerhost:$DOCKERHOST"
Then change http://localhost to http://dockerhost in your code.
For a more advance guide of how to customize the DOCKERHOST script, take a look at this post with a explanation of how it works.

Solution for Linux (kernel >=3.6).
Ok, your localhost server has a default docker interface docker0 with IP address 172.17.0.1. Your container started with default network settings --net="bridge".
Enable route_localnet for docker0 interface:
$ sysctl -w net.ipv4.conf.docker0.route_localnet=1
Add these rules to iptables:
$ iptables -t nat -I PREROUTING -i docker0 -d 172.17.0.1 -p tcp --dport 3306 -j DNAT --to 127.0.0.1:3306
$ iptables -t filter -I INPUT -i docker0 -d 127.0.0.1 -p tcp --dport 3306 -j ACCEPT
Create MySQL user with access from '%' that means - from anyone, excluding localhost:
CREATE USER 'user'#'%' IDENTIFIED BY 'password';
Change in your script the mysql-server address to 172.17.0.1.
From the kernel documentation:
route_localnet - BOOLEAN: Do not consider loopback addresses as martian source or destination while routing. This enables the use of 127/8 for local routing purposes (default FALSE).

This worked for me on an NGINX/PHP-FPM stack without touching any code or networking where the app's just expecting to be able to connect to localhost
Mount mysqld.sock from the host to inside the container.
Find the location of the mysql.sock file on the host running mysql:
netstat -ln | awk '/mysql(.*)?\.sock/ { print $9 }'
Mount that file to where it's expected in the docker:
docker run -v /hostpath/to/mysqld.sock:/containerpath/to/mysqld.sock
Possible locations of mysqld.sock:
/tmp/mysqld.sock
/var/run/mysqld/mysqld.sock
/var/lib/mysql/mysql.sock
/Applications/MAMP/tmp/mysql/mysql.sock # if running via MAMP

Until host.docker.internal is working for every platform, you can use my container acting as a NAT gateway without any manual setup:
https://github.com/qoomon/docker-host

Simplest solution for Mac OSX
Just use the IP address of your Mac. On the Mac run this to get the IP address and use it from within the container:
ifconfig | grep 'inet 192'| awk '{ print $2}'
As long as the server running locally on your Mac or in another docker container is listening to 0.0.0.0, the docker container will be able to reach out at that address.
If you just want to access another docker container that is listening on 0.0.0.0 you can use 172.17.0.1

Very simple and quick, check your host IP with ifconfig (linux) or ipconfig (windows) and then create a docker-compose.yml:
version: '3' # specify docker-compose version
services:
nginx:
build: ./ # specify the directory of the Dockerfile
ports:
- "8080:80" # specify port mapping
extra_hosts:
- "dockerhost:<yourIP>"
This way, your container will be able to access your host. When accessing your DB, remember to use the name you specified before, in this case dockerhost and the port of your host in which the DB is running.

Solution for Windows 10
Docker Community Edition 17.06.0-ce-win18 2017-06-28 (stable)
You can use DNS name of the host docker.for.win.localhost, to resolve to the internal IP. (Warning some sources mentioned windows but it should be win)
Overview
I needed to do something similar, that is connect from my Docker container to my localhost, which was running the Azure Storage Emulator and CosmosDB Emulator.
The Azure Storage Emulator by default listens on 127.0.0.1, while you can change the IP its bound too, I was looking for a solution that would work with default settings.
This also works for connecting from my Docker container to SQL Server and IIS, both running locally on my host with default port settings.

For windows,
I have changed the database url in spring configuration: spring.datasource.url=jdbc:postgresql://host.docker.internal:5432/apidb
Then build the image and run. It worked for me.

None of the answers worked for me when using Docker Toolbox on Windows 10 Home, but 10.0.2.2 did, since it uses VirtualBox which exposes the host to the VM on this address.

This is not an answer to the actual question. This is how I solved a similar problem. The solution comes totally from: Define Docker Container Networking so Containers can Communicate. Thanks to Nic Raboy
Leaving this here for others who might want to do REST calls between one container and another. Answers the question: what to use in place of localhost in a docker environment?
Get how your network looks like docker network ls
Create a new network docker network create -d my-net
Start the first container docker run -d -p 5000:5000 --network="my-net" --name "first_container" <MyImage1:v0.1>
Check out network settings for first container docker inspect first_container. "Networks": should have 'my-net'
Start the second container docker run -d -p 6000:6000 --network="my-net" --name "second_container" <MyImage2:v0.1>
Check out network settings for second container docker inspect second_container. "Networks": should have 'my-net'
ssh into your second container docker exec -it second_container sh or docker exec -it second_container bash.
Inside of the second container, you can ping the first container by ping first_container. Also, your code calls such as http://localhost:5000 can be replaced by http://first_container:5000

If you're running with --net=host, localhost should work fine. If you're using default networking, use the static IP 172.17.0.1.
See this - https://stackoverflow.com/a/48547074/14120621

For those on Windows, assuming you're using the bridge network driver, you'll want to specifically bind MySQL to the IP address of the hyper-v network interface.
This is done via the configuration file under the normally hidden C:\ProgramData\MySQL folder.
Binding to 0.0.0.0 will not work. The address needed is shown in the docker configuration as well, and in my case was 10.0.75.1.

Edit: I ended up prototyping out the concept on GitHub. Check out: https://github.com/sivabudh/system-in-a-box
First, my answer is geared towards 2 groups of people: those who use a Mac, and those who use Linux.
The host network mode doesn't work on a Mac. You have to use an IP alias, see: https://stackoverflow.com/a/43541681/2713729
What is a host network mode? See: https://docs.docker.com/engine/reference/run/#/network-settings
Secondly, for those of you who are using Linux (my direct experience was with Ubuntu 14.04 LTS and I'm upgrading to 16.04 LTS in production soon), yes, you can make the service running inside a Docker container connect to localhost services running on the Docker host (eg. your laptop).
How?
The key is when you run the Docker container, you have to run it with the host mode. The command looks like this:
docker run --network="host" -id <Docker image ID>
When you do an ifconfig (you will need to apt-get install net-tools your container for ifconfig to be callable) inside your container, you will see that the network interfaces are the same as the one on Docker host (eg. your laptop).
It's important to note that I'm a Mac user, but I run Ubuntu under Parallels, so using a Mac is not a disadvantage. ;-)
And this is how you connect NGINX container to the MySQL running on a localhost.

First see this answer for the options that you have to fix this problem. But if you use docker-compose you can add network_mode: host to your service and then use 127.0.0.1 to connect to the local host. This is just one of the options described in the answer above. Below you can find how I modified docker-compose.yml from https://github.com/geerlingguy/php-apache-container.git:
---
version: "3"
services:
php-apache:
+ network_mode: host
image: geerlingguy/php-apache:latest
container_name: php-apache
...
+ indicates the line I added.
[Additional info] This has also worked in version 2.2. and "host" or just 'host' are both worked in docker-compose.
---
version: "2.2"
services:
php-apache:
+ network_mode: "host"
or
+ network_mode: host
...

I disagree with the answer from Thomasleveil.
Making mysql bind to 172.17.42.1 will prevent other programs using the database on the host to reach it. This will only work if all your database users are dockerized.
Making mysql bind to 0.0.0.0 will open the db to outside world, which is not only a very bad thing to do, but also contrary to what the original question author wants to do. He explicitly says "The MySql is running on localhost and not exposing a port to the outside world, so its bound on localhost"
To answer the comment from ivant
"Why not bind mysql to docker0 as well?"
This is not possible. The mysql/mariadb documentation explicitly says it is not possible to bind to several interfaces. You can only bind to 0, 1, or all interfaces.
As a conclusion, I have NOT found any way to reach the (localhost only) database on the host from a docker container. That definitely seems like a very very common pattern, but I don't know how to do it.

Try this:
version: '3.5'
services:
yourservice-here:
container_name: container_name
ports:
- "4000:4000"
extra_hosts: # <---- here
- localhost:192.168.1.202
- or-vitualhost.local:192.168.1.202
To get 192.168.1.202, uses ifconfig
This worked for me. Hope this help!

In 7 years the question was asked, it is either docker has changed, or no one tried this way. So I will include my own answer.
I have found all answers use complex methods. Today, I have needed this, and found 2 very simple ways:
use ipconfig or ifconfig on your host and make note of all IP addresses. At least two of them can be used by the container.
I have a fixed local network address on WiFi LAN Adapter: 192.168.1.101. This could be 10.0.1.101. the result will change depending on your router
I use WSL on windows, and it has its own vEthernet address: 172.19.192.1
use host.docker.internal. Most answers have this or another form of it depending on OS. The name suggests it is now globally used by docker.
A third option is to use WAN address of the machine, or in other words IP given by the service provider. However, this may not work if IP is not static, and requires routing and firewall settings.

You need to know the gateway! My solution with local server was to expose it under 0.0.0.0:8000, then run docker with subnet and run container like:
docker network create --subnet=172.35.0.0/16 --gateway 172.35.0.1 SUBNET35
docker run -d -p 4444:4444 --net SUBNET35 <container-you-want-run-place-here>
So, now you can access your loopback through http://172.35.0.1:8000

Connect to the gateway address.
❯ docker network inspect bridge | grep Gateway
"Gateway": "172.17.0.1"
Make sure the process on the host is listening on this interface or on all interfaces and is started after docker. If using systemd, you can add the below to make sure it is started after docker.
[Unit]
After=docker.service
Example
❯ python -m http.server &> /dev/null &
[1] 149976
❯ docker run --rm python python -c "from urllib.request import urlopen;print(b'Directory listing for' in urlopen('http://172.17.0.1:8000').read())"
True

Here is my solution : it works for my case
set local mysql server to public access by comment
#bind-address = 127.0.0.1
in /etc/mysql/mysql.conf.d
restart mysql server
sudo /etc/init.d/mysql restart
run the following command to open user root access any host
mysql -uroot -proot
GRANT ALL PRIVILEGES ON *.* TO 'root'#'%' IDENTIFIED BY 'root' WITH
GRANT OPTION;
FLUSH PRIVILEGES;
create sh script : run_docker.sh
#!bin/bash
HOSTIP=`ip -4 addr show scope global dev eth0 | grep inet | awk '{print \$2}' | cut -d / -f 1`
docker run -it -d --name web-app \
--add-host=local:${HOSTIP} \
-p 8080:8080 \
-e DATABASE_HOST=${HOSTIP} \
-e DATABASE_PORT=3306 \
-e DATABASE_NAME=demo \
-e DATABASE_USER=root \
-e DATABASE_PASSWORD=root \
sopheamak/springboot_docker_mysql
run with docker-composer
version: '2.1'
services:
tomcatwar:
extra_hosts:
- "local:10.1.2.232"
image: sopheamak/springboot_docker_mysql
ports:
- 8080:8080
environment:
- DATABASE_HOST=local
- DATABASE_USER=root
- DATABASE_PASSWORD=root
- DATABASE_NAME=demo
- DATABASE_PORT=3306

You can get the host ip using alpine image
docker run --rm alpine ip route | awk 'NR==1 {print $3}'
This would be more consistent as you're always using alpine to run the command.
Similar to Mariano's answer you can use same command to set an environment variable
DOCKER_HOST=$(docker run --rm alpine ip route | awk 'NR==1 {print $3}') docker-compose up

you can use net alias for your machine
OSX
sudo ifconfig lo0 alias 123.123.123.123/24 up
LINUX
sudo ifconfig lo:0 123.123.123.123 up
then from the container you can see the machine by 123.123.123.123

The CGroups and Namespaces are playing major role in the Container Ecosystem.
Namespace provide a layer of isolation. Each container runs in a separate namespace and its access is limited to that namespace. The Cgroups controls the resource utilization of each container, whereas Namespace controls what a process can see and access the respective resource.
Here is the basic understanding of the solution approach you could follow,
Use Network Namespace
When a container spawns out of image, a network interface is defined and create. This gives the container unique IP address and interface.
$ docker run -it alpine ifconfig
By changing the namespace to host, cotainers networks does not remain isolated to its interface, the process will have access to host machines network interface.
$ docker run -it --net=host alpine ifconfig
If the process listens on ports, they'll be listened on the host interface and mapped to the container.
Use PID Namespace
By changing the Pid namespace allows a container to interact with other process beyond its normal scope.
This container will run in its own namespace.
$ docker run -it alpine ps aux
By changing the namespace to the host, the container can also see all the other processes running on the system.
$ docker run -it --pid=host alpine ps aux
Sharing Namespace
This is a bad practice to do this in production because you are breaking out of the container security model which might open up for vulnerabilities, and easy access to eavesdropper. This is only for debugging tools and understating the loopholes in container security.
The first container is nginx server. This will create a new network and process namespace. This container will bind itself to port 80 of newly created network interface.
$ docker run -d --name http nginx:alpine
Another container can now reuse this namespace,
$ docker run --net=container:http mohan08p/curl curl -s localhost
Also, this container can see the interface with the processes in a shared container.
$ docker run --pid=container:http alpine ps aux
This will allow you give more privileges to containers without changing or restarting the application. In the similar way you can connect to mysql on host, run and debug your application. But, its not recommend to go by this way. Hope it helps.

Until fix is not merged into master branch, to get host IP just run from inside of the container:
ip -4 route list match 0/0 | cut -d' ' -f3
(as suggested by #Mahoney here).

I solved it by creating a user in MySQL for the container's ip:
$ sudo mysql<br>
mysql> create user 'username'#'172.17.0.2' identified by 'password';<br>
Query OK, 0 rows affected (0.00 sec)
mysql> grant all privileges on database_name.* to 'username'#'172.17.0.2' with grant option;<br>
Query OK, 0 rows affected (0.00 sec)
$ sudo vim /etc/mysql/mysql.conf.d/mysqld.cnf
<br>bind-address = 172.17.0.1
$ sudo systemctl restart mysql.service
Then on container: jdbc:mysql://<b>172.17.0.1</b>:3306/database_name

Docker install causes host machine to be unreachable

I am installing the latest version of docker on a ubuntu 16.04 vmware. After install I cant ssh to the box.
Is docker making some network changes that cause this?
Never had this issue before

Our local workstation network is: 172.18.0.0/24
The docker0 interface is 172.18.0.0/16
netstat -rn had route for 172.18.0.0 -> docker0
We changed the docker0 interface subnet using : https://support.zenoss.com/hc/en-us/articles/203582809-How-to-Change-the-Default-Docker-Subnet
Reloaded docker and started containers.
Working as expected.

Check if your UFW rules somehow changed from the install.
$ sudo ufw status numbered
and if SSH is still running on the host machine.

How do I get rid of the HWaddr that docker0 is using?

I installed docker.io on CentOS several months ago and never used it for anything. I have a license for another product that is tied to my MAC address, but the HWaddr that docker0 is using causes the license installation to fail.
I've uninstalled docker, but ifconfig still shows docker0 with the same HWaddr. How do I get rid of the docker0 that ifconfig shows?
Thanks.

It took a reboot to remove the docker0 interface after running yum -y remove docker-io.x86_64.

My docker container has no internet

I had it working allright but now it stopped. I tried the following commands with no avail:
docker run -dns 8.8.8.8 base ping google.com
docker run base ping google.com
sysctl -w net.ipv4.ip_forward=1 - both on the host and on the container
All I get is unknown host google.com. Docker version 0.7.0
Any ideas?
P.S. ufw disabled as well

First thing to check is run cat /etc/resolv.conf in the docker container. If it has an invalid DNS server, such as nameserver 127.0.x.x, then the container will not be able to resolve the domain names into ip addresses, so ping google.com will fail.
Second thing to check is run cat /etc/resolv.conf on the host machine. Docker basically copies the host's /etc/resolv.conf to the container everytime a container is started. So if the host's /etc/resolv.conf is wrong, then so will the docker container.
If you have found that the host's /etc/resolv.conf is wrong, then you have 2 options:
Hardcode the DNS server in daemon.json. This is easy, but not ideal if you expect the DNS server to change.
Fix the hosts's /etc/resolv.conf. This is a little trickier, but it is generated dynamically, and you are not hardcoding the DNS server.
1. Hardcode DNS server in docker daemon.json
Edit /etc/docker/daemon.json
{
"dns": ["10.1.2.3", "8.8.8.8"]
}
Restart the docker daemon for those changes to take effect:
sudo systemctl restart docker
Now when you run/start a container, docker will populate /etc/resolv.conf with the values from daemon.json.
2. Fix the hosts's /etc/resolv.conf
A. Ubuntu 16.04 and earlier
For Ubuntu 16.04 and earlier, /etc/resolv.conf was dynamically generated by NetworkManager.
Comment out the line dns=dnsmasq (with a #) in /etc/NetworkManager/NetworkManager.conf
Restart the NetworkManager to regenerate /etc/resolv.conf :
sudo systemctl restart network-manager
Verify on the host: cat /etc/resolv.conf
B. Ubuntu 18.04 and later
Ubuntu 18.04 changed to use systemd-resolved to generate /etc/resolv.conf. Now by default it uses a local DNS cache 127.0.0.53. That will not work inside a container, so Docker will default to Google's 8.8.8.8 DNS server, which may break for people behind a firewall.
/etc/resolv.conf is actually a symlink (ls -l /etc/resolv.conf) which points to /run/systemd/resolve/stub-resolv.conf (127.0.0.53) by default in Ubuntu 18.04.
Just change the symlink to point to /run/systemd/resolve/resolv.conf, which lists the real DNS servers:
sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
Verify on the host: cat /etc/resolv.conf
Now you should have a valid /etc/resolv.conf on the host for docker to copy into the containers.

Fixed by following this advice:
[...] can you try to reset everything?
pkill docker
iptables -t nat -F
ifconfig docker0 down
brctl delbr docker0
docker -d
It will force docker to recreate the bridge and reinit all the network rules
https://github.com/dotcloud/docker/issues/866#issuecomment-19218300
Seems the interface was 'hung' somehow.
Update for more recent versions of docker:
The above answer might still get the job done for you but it has been quite a long time since this answer was posted and docker is more polished now so make sure you try these first before going into mangling with iptables and all.
sudo service docker restart or (if you are in a linux distro that does not use upstart) sudo systemctl restart docker

The intended way to restart docker is not to do it manually but use the service or systemctl command:
service docker restart
or
systemctl restart docker

Updating this question with an answer for OSX (using Docker Machine)
If you are running Docker on OSX using Docker Machine, then the following worked for me:
docker-machine restart
<...wait for it to restart, which takes up to a minute...>
docker-machine env
eval $(docker-machine env)
Then (at least in my experience), if you ping google.com from a container all will be well.

Tried all answers, none worked for me.
After a few hours of trying everything else I could find, this did the trick:
reboot
-_-

I do not know what I am doing but that worked for me :
OTHER_BRIDGE=br-xxxxx # this is the other random docker bridge (`ip addr` to find)
service docker stop
ip link set dev $OTHER_BRIDGE down
ip link set dev docker0 down
ip link delete $OTHER_BRIDGE type bridge
ip link delete docker0 type bridge
service docker start && service docker stop
iptables -t nat -A POSTROUTING ! -o docker0 -s 172.17.0.0/16 -j MASQUERADE
iptables -t nat -A POSTROUTING ! -o docker0 -s 172.18.0.0/16 -j MASQUERADE
service docker start

I was using DOCKER_OPTS="--dns 8.8.8.8" and later discovered and that my container didn't have direct access to internet but could access my corporate intranet. I changed DOCKER_OPTS to the following:
DOCKER_OPTS="--dns <internal_corporate_dns_address"
replacing internal_corporate_dns_address with the IP address or FQDN of our DNS and restarted docker using
sudo service docker restart
and then spawned my container and checked that it had access to internet.

No internet access can also be caused by missing proxy settings. In that case, --network host may not work either. The proxy can be configured by setting the environment variables http_proxy and https_proxy:
docker run -e "http_proxy=YOUR-PROXY" \
-e "https_proxy=YOUR-PROXY"\
-e "no_proxy=localhost,127.0.0.1" ...
Do not forget to set no_proxy as well, or all requests (including those to localhost) will go through the proxy.
More information: Proxy Settings in the Archlinux Wiki.

I was stumped when this happened randomly for me for one of my containers, while the other containers were fine. The container was attached to at least one non-internal network, so there was nothing wrong with the Compose definition. Restarting the VM / docker daemon did not help. It was also not a DNS issue because the container could not even ping an external IP. What solved it for me was to recreate the docker network(s). In my case, docker-compose down && docker-compose up worked.
Compose
This forces the recreation of all networks of all the containers:
docker-compose down && docker-compose up
Swarm mode
I suppose you just remove and recreate the service, which recreates the service's network(s):
docker service rm some-service
docker service create ...
If the container's network(s) are external
Simply remove and recreate the external networks of that service:
docker network rm some-external-network
docker network create some-external-network

For me it was the host's firewall. I had to allow DNS on the host's firewall. And also had to restart docker after changing the host firewall setting.

for me, my problem was because of iptables-services was not installed, this worked for me (CentOS):
sudo yum install iptables-services
sudo service docker restart

Other answers have stated that the docker0 interface (bridge) can be the source of the problem. On Ubuntu 20.04 I observed that the interface was missing its IP address (to be checked with ip addr show dev docker0). Restarting Docker alone did not help. I had to delete the bridge interface manually.
sudo ip link delete docker0
sudo systemctl restart docker

You may have started your docker with dns options --dns 172.x.x.x
I had the same error and removed the options from /etc/default/docker
The lines:
# Use DOCKER_OPTS to modify the daemon startup options.
DOCKER_OPTS="--dns 172.x.x.x"

On centos 8,
My problem was that I did not install & start iptables before starting docker service. Make sure iptables service is up and running before you start docker service.

Sharing a simple and working solution for posterity. When we run a docker container without explicitly mentioning the --network flag, it connects to its default bridge network which prohibits connecting to the outside world. To resolve this issue, we have to create our own bridge network(user-defined bridge) and have to explicitly mention it with the docker run command.
docker network create --driver bridge mynetwork
docker run -it --network mynetwork image:version

it help me:
sudo ip link delete docker0
sudo systemctl stop docker.socket
sudo systemctl stop docker.service
sudo systemctl start docker.socket
sudo systemctl start docker.service
NOTE: after this, interface docker0 must have ip adress smth like that:
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0

If you're on OSX, you might need to restart your machine after installing Docker. This has been an issue at times.

For me it was an iptables forwarding rule. For some reason the following rule, when coupled with docker's iptables rules, caused all outbound traffic from containers to hit localhost:8080:
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-ports 8080
iptables -t nat -I OUTPUT -p tcp -d 127.0.0.1 --dport 80 -j REDIRECT --to-ports 8080

I had the problem on Ubuntu 18.04. However the problem was with the DNS. I was in a corporate network that has its own DNS server and block other DNS servers. This is to block some websites (porn, torrents, ... so on )
To resolve your problem
find your DNS on host machine
use --dns your_dns as suggested
by #jobin
docker run --dns your_dns -it --name cowsay --hostname cowsay debian bash

For Ubuntu 19.04 using openconnect 8.3 for VPN, I had to symlink /etc/resolve.conf to the one in systemd (opposite of answerby wisbucky )
sudo ln -sf /etc/resolv.conf /run/systemd/resolve/resolv.conf
Steps to debug
Connect to Company VPN
Look for correct VPN settings in either /etc/resolv.conf or /run/systemd/resolve/resolv.conf
Whichever has the correct DNS settings, we'll symlink that to the other file
( Hint: Place one with correct settings on the left of assignment )
Docker version: Docker version 19.03.0-rc2, build f97efcc

for me, using centos 7.4, it was not issue of /etc/resolve.conf, iptables, iptables nat rules nor docker itself. The issue is the host missing the package bridge-utils which docker require to build the bridge using command brctl. yum install -y bridge-utils and restart docker, solve the problem.

On windows (8.1) I killed the virtualbox interface (via taskmgr) and it solved the issue.

Originally my docker container was able to reach the external internet (This is a docker service/container running on an Amazon EC2).
Since my app is an API, I followed up the creation of my container (it succeeded in pulling all the packages it needed) with updating my IP Tables to route all traffic from port 80 to the port that my API (running on docker) was listening on.
Then, later when I tried rebuilding the container it failed. After much struggle, I discovered that my previous step (setting the IPTable port forwarding rule) messed up the docker's external networking capability.
Solution: Stop your IPTable service:
sudo service iptables stop
Restart The Docker Daemon:
sudo service docker restart
Then, try rebuilding your container. Hope this helps.
Follow Up
I completely overlooked that I did not need to mess with the IP Tables to forward incoming traffic to 80 to the port that the API running on docker was running on. Instead, I just aliased port 80 to the port the API in docker was running on:
docker run -d -p 80:<api_port> <image>:<tag> <command to start api>

Just adding this here in case someone runs into this issue within a virtualbox container running docker. I reconfigured the virtualbox network to bridged instead of nat, and the problem went away.

There are lot of good answer already. I faced similar problem in my orange pi pc running armbian recently. Docker container was blocked to internet. This command solve the problem in my case. So I like to share it
docker run --security-opt seccomp=unconfined imageName

I've tried most answers in here, but the only thing that worked was re-creating the network:
$ docker network rm the-network
$ docker network create --driver=bridge the-network
I also needed to re-create the docker container that used it:
$ sudo docker create --name the-name --network the-network
Then it started with internet access.

I am on Arch Linux and after trying all the above answers I realized that I had a firewall enabled in my machine, nftables, and disabling it did the trick. I did :
sudo systemctl disable nftables
sudo systemctl stop nftables
sudo reboot
My network cards:
➜ ~ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp1s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
link/ether 68:f7:28:84:e7:fe brd ff:ff:ff:ff:ff:ff
3: wlp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DORMANT group default qlen 1000
link/ether d0:7e:35:d2:42:6d brd ff:ff:ff:ff:ff:ff
4: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default
link/ether 02:42:43:3f:ff:94 brd ff:ff:ff:ff:ff:ff
5: br-c51881f83e32: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
link/ether 02:42:ae:34:49:c3 brd ff:ff:ff:ff:ff:ff
6: br-c5b2a1d25a86: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
link/ether 02:42:72:d3:6f:4d brd ff:ff:ff:ff:ff:ff
8: veth56f42a2#if7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master docker0 state UP mode DEFAULT group default
link/ether 8e:70:36:10:4e:83 brd ff:ff:ff:ff:ff:ff link-netnsid 0
and my firewal configuration, /etc/nftables.conf, which I now disabled and will futurely try to improve so I can have the docker0 network card rules setup correctly:
#!/usr/bin/nft -f
# vim:set ts=2 sw=2 et:
# IPv4/IPv6 Simple & Safe firewall ruleset.
# More examples in /usr/share/nftables/ and /usr/share/doc/nftables/examples/.
table inet filter
delete table inet filter
table inet filter {
chain input {
type filter hook input priority filter
policy drop
ct state invalid drop comment "early drop of invalid connections"
ct state {established, related} accept comment "allow tracked connections"
iifname lo accept comment "allow from loopback"
ip protocol icmp accept comment "allow icmp"
meta l4proto ipv6-icmp accept comment "allow icmp v6"
#tcp dport ssh accept comment "allow sshd"
pkttype host limit rate 5/second counter reject with icmpx type admin-prohibited
counter
}
chain forward {
type filter hook forward priority filter
policy drop
}

If you're running Docker rootless and facing this issue, during its installation, iptables may not be configured properly, mainly because of using --skip-iptables option when Docker complained about iptables:
[ERROR] Missing system requirements. Run the following commands to
[ERROR] install the requirements and run this tool again.
[ERROR] Alternatively iptables checks can be disabled with --skip-iptables .
########## BEGIN ##########
sudo sh -eux <<EOF
# Load ip_tables module
modprobe ip_tables
EOF
########## END ##########
Let's check if this is the issue: is ip_tables kernel module loaded?
sudo modprobe ip_tables
If there is no output, this answer may not help you (you could try anyway). Otherwise, the output's something like this:
modprobe: FATAL: Module ip_tables not found in directory /lib/modules/5.18.9-200.fc36.x86_64
Let's fix it!
First, uninstall Docker rootless (no need to stop the service via systemctl, the script handles that):
dockerd-rootless-setuptool.sh uninstall --skip-iptables
Ensure iptables package is installed, although it's shipped by default by major distributions.
Now, make ip_tables module visible to modprobe and install it (thanks to this):
sudo depmod
sudo modprobe ip_tables
Now, re-install Docker rootless:
dockerd-rootless-setuptool.sh install
If it doesn't bother about iptables, you're done and problem should be fixed. Don't forget to enable the service (i.e. systemctl enable --user --now docker)!

For me iwas facing the same issue as user of redhat/centos/fedora using podman
firewall-cmd --zone=public --add-masquerade
firewall-cmd --permanent --zone=public --add-masquerade
for more firewalld and podman (or docker) – no internet in the container and could not resolve host

I also encountered such an issue while trying to set up a project using Docker-Compose on Ubuntu.
The Docker had no access to internet at all, when I tried to ping any IP address or nslookup some URL - it failed all the time.
I tried all the possible solutions with DNS resolution described above to no avail.
I spent the whole day trying to find out what the heck is going on, and finally found out that the cause of all the trouble was the antivirus, in particular it's firewall which for some reason blocked Docker from getting the IP address and port.
When I disabled it - everything worked fine.
So, if you have an antivirus installed and nothing helps fix the issue - the problem could be the firewall of the antivirus.

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