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From inside of a Docker container, how do I connect to the localhost of the machine?
(41 answers)
Closed 12 months ago.
I have a docker container running jenkins. As part of the build process, I need to access a web server that is run locally on the host machine. Is there a way the host web server (which can be configured to run on a port) can be exposed to the jenkins container?
I'm running docker natively on a Linux machine.
UPDATE:
In addition to #larsks answer below, to get the IP address of the Host IP from the host machine, I do the following:
ip addr show docker0 | grep -Po 'inet \K[\d.]+'
For all platforms
Docker v 20.10 and above (since December 14th 2020)
On Linux, add --add-host=host.docker.internal:host-gateway to your Docker command to enable this feature. (See below for Docker Compose configuration.)
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.
To enable this in Docker Compose on Linux, add the following lines to the container definition:
extra_hosts:
- "host.docker.internal:host-gateway"
For macOS and Windows
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
MacOS with earlier 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
When running Docker natively on Linux, you can access host services using the IP address of the docker0 interface. From inside the container, this will be your default route.
For example, on my system:
$ ip addr show docker0
7: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
valid_lft forever preferred_lft forever
inet6 fe80::f4d2:49ff:fedd:28a0/64 scope link
valid_lft forever preferred_lft forever
And inside a container:
# ip route show
default via 172.17.0.1 dev eth0
172.17.0.0/16 dev eth0 src 172.17.0.4
It's fairly easy to extract this IP address using a simple shell
script:
#!/bin/sh
hostip=$(ip route show | awk '/default/ {print $3}')
echo $hostip
You may need to modify the iptables rules on your host to permit
connections from Docker containers. Something like this will do the
trick:
# iptables -A INPUT -i docker0 -j ACCEPT
This would permit access to any ports on the host from Docker
containers. Note that:
iptables rules are ordered, and this rule may or may not do the
right thing depending on what other rules come before it.
you will only be able to access host services that are either (a)
listening on INADDR_ANY (aka 0.0.0.0) or that are explicitly
listening on the docker0 interface.
If you are using Docker on MacOS or Windows 18.03+, you can connect to the magic hostname host.docker.internal.
Lastly, under Linux you can run your container in the host network namespace by setting --net=host; in this case localhost on your host is the same as localhost inside the container, so containerized service will act like non-containerized services and will be accessible without any additional configuration.
Use --net="host" in your docker run command, then localhost in your docker container will point to your docker host.
The answer is...
Replace http://127.0.0.1 or http://localhost with http://host.docker.internal.
Why?
Source in the docs of Docker.
My google search brought me to here, and after digging in the comments I found it's a duplicate of From inside of a Docker container, how do I connect to the localhost of the machine?. I voted for closing this one as a duplicate, but since people (including myself!) often scroll down on the answers rather than reading the comments carefully, here is a short answer.
For linux systems, you can – starting from major version 20.04 of the docker engine – now also communicate with the host via host.docker.internal. This won't work automatically, but you need to provide the following run flag:
--add-host=host.docker.internal:host-gateway
See
https://github.com/moby/moby/pull/40007#issuecomment-578729356
https://github.com/docker/for-linux/issues/264#issuecomment-598864064
Solution with docker-compose:
For accessing to host-based service, you can use network_mode parameter
https://docs.docker.com/compose/compose-file/#network_mode
version: '3'
services:
jenkins:
network_mode: host
EDIT 2020-04-27: recommended for use only in local development environment.
EDIT 2021-09-21: IHaveHandedInMyResignation wrote it does not work for Mac and Windows. Option is supported only for Linux
I created a docker container for doing exactly that https://github.com/qoomon/docker-host
You can then simply use container name dns to access host system e.g.
curl http://dockerhost:9200
Currently the easiest way to do this on Mac and Windows is using host host.docker.internal, that resolves to host machine's IP address. Unfortunately it does not work on linux yet (as of April 2018).
We found that a simpler solution to all this networking junk is to just use the domain socket for the service. If you're trying to connect to the host anyway, just mount the socket as a volume, and you're on your way. For postgresql, this was as simple as:
docker run -v /var/run/postgresql:/var/run/postgresql
Then we just set up our database connection to use the socket instead of network. Literally that easy.
I've explored the various solution and I find this the least hacky solution:
Define a static IP address for the bridge gateway IP.
Add the gateway IP as an extra entry in the extra_hosts directive.
The only downside is if you have multiple networks or projects doing this, you have to ensure that their IP address range do not conflict.
Here is a Docker Compose example:
version: '2.3'
services:
redis:
image: "redis"
extra_hosts:
- "dockerhost:172.20.0.1"
networks:
default:
ipam:
driver: default
config:
- subnet: 172.20.0.0/16
gateway: 172.20.0.1
You can then access ports on the host from inside the container using the hostname "dockerhost".
For docker-compose using bridge networking to create a private network between containers, the accepted solution using docker0 doesn't work because the egress interface from the containers is not docker0, but instead, it's a randomly generated interface id, such as:
$ ifconfig
br-02d7f5ba5a51: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.32.1 netmask 255.255.240.0 broadcast 192.168.47.255
Unfortunately that random id is not predictable and will change each time compose has to recreate the network (e.g. on a host reboot). My solution to this is to create the private network in a known subnet and configure iptables to accept that range:
Compose file snippet:
version: "3.7"
services:
mongodb:
image: mongo:4.2.2
networks:
- mynet
# rest of service config and other services removed for clarity
networks:
mynet:
name: mynet
ipam:
driver: default
config:
- subnet: "192.168.32.0/20"
You can change the subnet if your environment requires it. I arbitrarily selected 192.168.32.0/20 by using docker network inspect to see what was being created by default.
Configure iptables on the host to permit the private subnet as a source:
$ iptables -I INPUT 1 -s 192.168.32.0/20 -j ACCEPT
This is the simplest possible iptables rule. You may wish to add other restrictions, for example by destination port. Don't forget to persist your iptables rules when you're happy they're working.
This approach has the advantage of being repeatable and therefore automatable. I use ansible's template module to deploy my compose file with variable substitution and then use the iptables and shell modules to configure and persist the firewall rules, respectively.
This is an old question and had many answers, but none of those fit well enough to my context. In my case, the containers are very lean and do not contain any of the networking tools necessary to extract the host's ip address from within the container.
Also, usin the --net="host" approach is a very rough approach that is not applicable when one wants to have well isolated network configuration with several containers.
So, my approach is to extract the hosts' address at the host's side, and then pass it to the container with --add-host parameter:
$ docker run --add-host=docker-host:`ip addr show docker0 | grep -Po 'inet \K[\d.]+'` image_name
or, save the host's IP address in an environment variable and use the variable later:
$ DOCKERIP=`ip addr show docker0 | grep -Po 'inet \K[\d.]+'`
$ docker run --add-host=docker-host:$DOCKERIP image_name
And then the docker-host is added to the container's hosts file, and you can use it in your database connection strings or API URLs.
For me (Windows 10, Docker Engine v19.03.8) it was a mix of https://stackoverflow.com/a/43541732/7924573 and https://stackoverflow.com/a/50866007/7924573 .
change the host/ip to host.docker.internal
e.g.: LOGGER_URL = "http://host.docker.internal:8085/log"
set the network_mode to bridge (if you want to maintain the port forwarding; if not use host):
version: '3.7'
services:
server:
build: .
ports:
- "5000:5000"
network_mode: bridge
or alternatively: Use --net="bridge" if you are not using docker-compose (similar to https://stackoverflow.com/a/48806927/7924573)
As pointed out in previous answers: This should only be used in a local development environment.
For more information read: https://docs.docker.com/compose/compose-file/#network_mode and https://docs.docker.com/docker-for-windows/networking/#use-cases-and-workarounds
You can access the local webserver which is running in your host machine in two ways.
Approach 1 with public IP
Use host machine public IP address to access webserver in Jenkins docker container.
Approach 2 with the host network
Use "--net host" to add the Jenkins docker container on the host's network stack. Containers which are deployed on host's stack have entire access to the host interface. You can access local webserver in docker container with a private IP address of the host machine.
NETWORK ID NAME DRIVER SCOPE
b3554ea51ca3 bridge bridge local
2f0d6d6fdd88 host host local
b9c2a4bc23b2 none null local
Start a container with the host network
Eg: docker run --net host -it ubuntu and run ifconfig to list all available network IP addresses which are reachable from docker container.
Eg: I started a nginx server in my local host machine and I am able to access the nginx website URLs from Ubuntu docker container.
docker run --net host -it ubuntu
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
a604f7af5e36 ubuntu "/bin/bash" 22 seconds ago Up 20 seconds ubuntu_server
Accessing the Nginx web server (running in local host machine) from Ubuntu docker container with private network IP address.
root#linuxkit-025000000001:/# curl 192.168.x.x -I
HTTP/1.1 200 OK
Server: nginx/1.15.10
Date: Tue, 09 Apr 2019 05:12:12 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Tue, 26 Mar 2019 14:04:38 GMT
Connection: keep-alive
ETag: "5c9a3176-264"
Accept-Ranges: bytes
In almost 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.
PS: Although pretty identical to this question here, and I posted this answer there, I first found this post, so I post it here too as may forget my own answer.
The simplest option that worked for me was,
I used the IP address of my machine on the local network(assigned by the router)
You can find this using the ifconfig command
e.g
ifconfig
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
options=400<CHANNEL_IO>
ether f0:18:98:08:74:d4
inet 192.168.178.63 netmask 0xffffff00 broadcast 192.168.178.255
media: autoselect
status: active
and then used the inet address. This worked for me to connect any ports on my machine.
When you have two docker images "already" created and you want to put two containers to communicate with one-another.
For that, you can conveniently run each container with its own --name and use the --link flag to enable communication between them. You do not get this during docker build though.
When you are in a scenario like myself, and it is your
docker build -t "centos7/someApp" someApp/
That breaks when you try to
curl http://172.17.0.1:localPort/fileIWouldLikeToDownload.tar.gz > dump.tar.gz
and you get stuck on "curl/wget" returning no "route to host".
The reason is security that is set in place by docker that by default is banning communication from a container towards the host or other containers running on your host.
This was quite surprising to me, I must say, you would expect the echosystem of docker machines running on a local machine just flawlessly can access each other without too much hurdle.
The explanation for this is described in detail in the following documentation.
http://www.dedoimedo.com/computers/docker-networking.html
Two quick workarounds are given that help you get moving by lowering down the network security.
The simplest alternative is just to turn the firewall off - or allow all. This means running the necessary command, which could be systemctl stop firewalld, iptables -F or equivalent.
Related
The question is basic: how to I connect to the localhost of the host machine from inside of a Docker container?
I tried answers from this post, using add-host host.docker.internal:host-gateway or writing --network=host when running my container but none of these methods seem to work.
I have a simple hello world webserver up on my machine, and I can see it's contents with curl localhost:8000 from my host, but I can't curl it from inside the container. I tried curl host.docker.internal:8000, curl localhost:8000, and curl 127.0.0.1:8000 from inside the container (based on the solution I used to make localhost available there) but none of them seem to work and I get a Connection refused error every time.
I asked somebody else to try this out for me on their own machine and it worked for them, so I don't think I'm doing anything wrong.
Does anybody have any idea what is wrong with my containers?
Host machine: Ubuntu 20.04.01
Docker version: 20.10.7
Used image: Ubuntu 20.04 (and i386/ubuntu18.04)
Temporary solution
This does not completely solve the problem for production purposes, but at least in order to get the localhost working, by adding these lines into docker-compose.yml it solved my issue for now (source):
services:
my-service:
network_mode: host
I am using apache nifi to use Java REST endpoints with the same ubuntu and docker versions, so in my case, it looks like this:
services:
nifi:
network_mode: host
After changing docker-compose.yml, I recommend stopping docker container, removing containers(docker-compose rm - do not use if you need some containers, otherwise use docker container rm container_id) and build with docker-compose up --build again.
In this case, I needed to use another localhost IP for my service to access with a browser (nifi started on other ip - 127.0.1.1 but works fine as well).
Searching for the problem / deeper into ubuntu-docker networking
Firstly, I will write down some useful commands that may be useful to find out a solution for the docker-ubuntu networking issue:
ip a - show all routing, network devices, interfaces and tunnels (mainly I can observe state DOWN with docker0)
ifconfig - list all interfaces
brctl show - ethernet bridge administration (docker0 has no attached interface / veth pair)
docker network ls - manages docker networks - names, drivers, scope...
docker network inspect bridge - I can see for docker0 bridge has no attached docker containers - empty and not used bridge
(useful link for ubuntu-docker networking explanation)
I guess that problem lays within veth pair (see link above), because when docker-compose occurs, there is a new bridge created (not docker0) that is connected to veth pair in my case, and docker0 is not used. My guess is that if docker0 is used, then host.docker.internal:host-gateway would work. Somehow in ubuntu networking, there is docker0 not used as the default bridge and this maybe should be changed.
I don't have much time left actually, well, I suppose someone can use this information and resolve the core of the problem later on.
Here is my situation：
First，I run a MySQL container(IP:172.17.0.2) on centOS;
Then I run a Nacos contanier with specified datasource(MySQL above) on the same host, but i didn't use the ip of the MySQL container, instead I used the ip of the bridge Gateway(172.17.0.1)(two containers both link to the default bridge).
What surprised me was that Nacos works well, it can query config data from MySQL container normally.
How did this happen? I have read some documention but didn't get the answer.It really confused me.
On modern Docker installations, try to avoid using the default bridge network. docker network create a network (it doesn't need any special options, but it does need to be created) and then launch your containers on --net that network. If you're using Compose, it creates a ("user bridge") network named default for you.
On your CentOS host, if you run ifconfig, you should see a docker0 interface with the 172.17.0.1 address. When you launch a container with the docker run -p option, that container is accessible via the first port number on all host interfaces, including the docker0 interface.
Meanwhile, inside a container (on the default bridge network), it sees that same IP address as the normal IPv4 gateway address (try docker run --rm busybox route -n). So, when you connect to 172.17.0.1:3306, you're connecting out to the host, and then connecting to the published port of the database container.
This isn't a totally standard way to connect between containers, though it will work. You should prefer using Docker named networks, which will let you connect to another container using the container's name without manually doing any IP-address lookups. If you really can't move off of the default bridge network, then the standard approach is to --link to the other container, but this entire path is considered outdated.
I have a mongodb docker container I only want to have access to it from inside of my server, not out side. even I blocked the port 27017/tcp with firewall-cmd but it seems that docker is still available to public.
I am using linux centos 7
and docker-compose for setting up docker
I resolved the same problem adding an iptables rule that blocks 27017 port on public interface (eth0) at the top of chain DOCKER:
iptables -I DOCKER 1 -i eth0 -p tcp --dport 27017 -j DROP
Set the rule after docker startup
Another thing to do is to use non-default port for mongod, modify docker-compose.yml (remember to add --port=XXX in command directive)
For better security I suggest to put your server behind an external firewall
If you have your application in one container and MongoDb in other container what you need to do is to connect them together by using a network that is set to be internal.
See Documentation:
Internal
By default, Docker also connects a bridge network to it to provide
external connectivity. If you want to create an externally isolated
overlay network, you can set this option to true.
See also this question
Here's the tutorial on networking (not including internal but good for understanding)
You may also limit traffic on MongoDb by Configuring Linux iptables Firewall for MongoDB
for creating private networks use some IPs from these ranges:
10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255
more read on Wikipedia
You may connect a container to more than one network so typically an application container is connected to the outside world network (external) and internal network. The application communicates with database on internal network and returns some data to the client via external network. Database is connected only to the internal network so it is not seen from the outside (internet)
I found a post here may help enter link description here. Just post it here for people who needed it in future.
For security concern we need both hardware firewall and OS firewall enabled and configured properly. I found that firewall protection is ineffective for ports opened in docker container listened on 0.0.0.0 though firewalld service was enabled at that time.
My situation is :
A server with Centos 7.9 and Docker version 20.10.17 installed
A docker container was running with port 3000 opened on 0.0.0.0
The firewalld service had started with the command systemctl start firewalld
Only ports 22 should be allow access outside the server as the firewall configured.
It was expected that no one others could access port 3000 on that server, but the testing result was opposite. Port 3000 on that server was accessed successfully from any other servers. Thanks to the blog post, I have had my server under firewall protected.
Questions like seem to be asked but I really don't get it at all.
I have a window 10 dev machine host with docker for windows installed. Besides others networks it has DockerNAT netwrok with IP 10.0.75.1
I run some containers with docker-compose:
version: '2'
services:
service_a:
build: .
container_name: docker_a
It created some network bla_default, container has IP 172.18.0.4, ofcource I can not connect to 172.18.0.4 from host - it doesn't have any netwrok interface for this.
What should I do to be able to access this container from HOST machine? (by IP) and if possible by some DNS name? What should I add to my docker-compose.yml, how to configure netwroks?
For me it should be something basic, but I really don't understand how all this stuff works and to access to container from host directly.
Allow access to internal docker networks from dev machine:
route /P add 172.0.0.0 MASK 255.0.0.0 10.0.75.2
Then use this https://github.com/aacebedo/dnsdock to enable DNS discovery.
Tips:
> docker run -d -v /var/run/docker.sock:/var/run/docker.sock --name dnsdock --net bridge -p 53:53/udp aacebedo/dnsdock:latest-amd64
> add 127.0.0.1 as DNS server on dev machine
> Use labels described in docs to have pretty dns names for containers
So the answer on the original question:
YES WE CAN!
Oh, this not actual.
MAKE DOCKER GREAT AGAIN!
The easiest option is port mapping: https://docs.docker.com/compose/compose-file/#/ports
just add
ports:
- "8080:80"
to the service definition in compose. If your service listens on port 80, requests to localhost:8080 on your host will be forwarded to the container. (I'm using docker machine, so my docker host is another IP, but I think localhost is how docker for windows appears)
Treating the service as a single process listening on one (or a few) ports has worked best for me, but if you want to start reading about networking options, here are some places to dig in:
https://docs.docker.com/engine/userguide/networking/
Docker's official page on networking - a very high level introduction, with most of the detail on the default bridge behavior.
http://www.linuxjournal.com/content/concerning-containers-connections-docker-networking
More information on network layout within a docker host
http://www.dasblinkenlichten.com/docker-networking-101-host-mode/
Host mode is kind of mysterious, and I'm curious if it works similarly on windows.
I would like to remove the interface docker0. It would be better to avoid creating the interface docker0 when starting the service and using directly the eth0.
To delete the interface, use:
ip link delete docker0
You may require sudo privilege.
By default, the Docker server creates and configures the host system’s docker0 interface as an Ethernet bridge inside the Linux kernel that can pass packets back and forth between other physical or virtual network interfaces so that they behave as a single Ethernet network.
Look at Understand Docker container networks and Customize the docker0 bridge
When you install Docker, it creates three networks automatically. You can list these networks using the docker network ls command:
$ docker network ls
Historically, these three networks (bridge, none, host) are part of Docker’s implementation. When you run a container you can use the --network flag to specify which network you want to run a container on. These three networks are still available to you.
The bridge network represents the docker0 network present in all Docker installations. Unless you specify otherwise with the docker run --network= option, the Docker daemon connects containers to this network by default. You can see this bridge as part of a host’s network stack by using the ifconfig command on the host.
I support #gile's solution.
Be careful when removing interfaces. I do not recommend you to remove bridge docker0 (the default docker0 is as a bridge - in my case).
The documentation says:
Bridge networks are usually used when you are in standalone containers
that need to communicate.
https://docs.docker.com/network/#network-drivers
If you want to remove this interface, you can use the following tools in addition to the above solutions (for removing / adding interfaces I suggest you use the tools provided with the docker):
nmcli connection delete docker0
docker network rm docker0
brctl delbr docker0
If you don't want to create docker0 interface at all when docker starts then edit daemon.json(which is configuration file for docker) file to add line "bridge": "none" line to that json.
I have trouble with connecting to VPN after installing docker. The solution would be the following:
You can see the ip route table by executing ip route command in linux. Then delete any domains start with 172.16.x.x.
For example:
> ip route
default via 192.168.1.1 dev wlp2s0 proto dhcp metric 20600
169.254.0.0/16 dev wlp2s0 scope link metric 1000
172.16.14.0/24 dev vmnet8 proto kernel scope link src 172.16.14.1
172.16.57.0/24 dev vmnet1 proto kernel scope link src 172.16.57.1
192.168.1.0/24 dev wlp2s0 proto kernel scope link src 192.168.1.4 metric 600
Then delete them like the following:
sudo ip route del 172.16.14.0/24 dev vmnet8 proto kernel scope link src 172.16.14.1
sudo ip route del 172.16.57.0/24 dev vmnet1 proto kernel scope link src 172.16.57.1