WIthin a Docker container, I would like to connect to a MySQL database that resides on the local network. However, I get errors because it can not find the host name, so my current hot fix is to hardcode the IP (which is bound to change at some time).
Hence; is it possible to forward a hostname from the host machine to the Docker container at docker run?
Yes, it is possible. Just inject hostname variable when run docker run command:
$ hostname
np-laptop
$ docker run -ti -e HOSTNAME=$(hostname) alpine:3.7
/ # env
HOSTNAME=np-laptop
SHLVL=1
HOME=/root
TERM=xterm
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/
Update:
I think you can do two things with docker run for your particular case:
1. Bind /etc/hosts file from the host to a container.
2. Define any dns server you want inside a container with --dns flag.
So, finally the command is:
docker run -ti -v /etc/hosts:/etc/hosts --dns=<IP_of_DNS> alpine:3.7
Docker containers by default has access to the host network, and they're able to resolve DNS names using DNS servers configured on the host, so it should work out of the box.
I remember having similar problem in my corporate network, I solved it by referencing in the app the remote server with FQDN - our-database.mycompany.com instad just using our-database.
Hope this helps.
People has asked similar questions and got good answers:
How do I pass environment variables to Docker containers?
Alternatively you can configure the DHCP/DNS server that serves the docker machines to resolve the hostnames properly. DDNS is another option that can simplify configuration as well.
I have a very special scenario. A virtual machine containing some docker containers. One of this containers needs to know the host ip. The problem is if I pass the host ip on container build or using -e on docker run command, it remains "static" (always the same, the one of that moment) on the container.
That vm can be on a laptop and the laptop is moving from different networks and the vm host ip can be different each reboot.
This special container has the --restart=always and is not built or "docker run" again... only once. And as I said, I need the host's ip on each reboot to configure the service inside the container on it's entrypoint because the container has a bind dns server which must load a zone with some dns entries that must be pointing to itself (the host's ip). An environment var would be great if possible. These are my data:
The "normal" lauch
The end of my Dockerfile:
....
....
ENTRYPOINT ["/etc/bind/entrypoint.sh"]
CMD ["/usr/sbin/named", "-g", "-c", "/etc/bind/named.conf", "-u", "bind"]
Entrypoint file (the regex works fine if the var could have the right value):
#!/bin/bash
sed -ri "s/IN A.*/IN A $HOSTIP/" /etc/bind/db.my.zone
exec "$#"
Docker run cmd:
docker run --name myContainer -d --restart=always -p 53:53 -p 53:53/udp myImage
What I tried:
I guess the entrypoint is ok and shouldn't be modified if I can provide to it a var with the right value.
If I put a -e on docker run command, it is "hardcoded" forever with the same ip always even if the host is on different networks:
docker run -e HOSTIP=$(ifconfig eth0 | grep netmask | awk '{print $2}') --name myContainer \
-d --restart=always -p 53:53 -p 53:53/udp myImage
I tried unsuccessfully also modifying the CMD on Dockerfile:
CMD (export HOSTIP=$(ifconfig eth0 | grep netmask | awk '{print $2}'));/usr/sbin/named -g -c /etc/bind/named.conf -u bind
Is possible to achieve something like this? Thanks.
There is the file /proc/net/tcp on the host machine that shows all the opened sockets. In particular, the second column is the local_address of the host interface.
The values in this column are store as little-endian four-byte hexadecimal numbers. To convert these to IP addresses take a look here
Thus when starting you container, you can mount this file from the host onto the container -v /proc/net/tcp:/host-tcp and read the host ip addresses which will be constantly reflected in this file.
I finally solved it. Thank you #yamenk for your answer, it gave me the idea, upvoting.
Finally what I did:
I created a simple script on host which is getting host ip and writting it into another file.
I set that script to be launched on every host boot before docker start.
I mapped the file with the ip into the container using -v on docker run command.
I set my entrypoint to get the ip from that file containing the ip and modifying with sed the needed container config files
Everything working! if I boot the vm (the host machine) on another different network, it gets the ip and the container is able to reconfigure itself before starting with the new ip.
I want to make it so that the Docker container I spin up use the same /etc/hosts settings as on the host machine I run from. Is there a way to do this?
I know there is an --add-host option with docker run, but that's not exactly what I want because the host machine's /etc/hosts file may be different on different machines, so it's not great for me to hardcode exact IP addresses/hosts with --add-host.
Use --network=host in the docker run command. This tells Docker to make the container use the host's network stack. You can learn more here.
Add a standard hosts file -
docker run -it ubuntu cat /etc/hosts
Add a mapping for server 'foo' -
docker run -it --add-host foo:10.0.0.3 ubuntu cat /etc/hosts
Add mappings for multiple servers
docker run -it --add-host foo:10.0.0.3 --add-host bar:10.7.3.21 ubuntu cat /etc/hosts
Reference - Docker Now Supports Adding Host Mappings
extra_hosts (in docker-compose.yml)
https://github.com/compose-spec/compose-spec/blob/master/spec.md#extra_hosts
Add hostname mappings. Use the same values as the docker client --add-host parameter.
extra_hosts:
- "somehost:162.242.195.82"
- "otherhost:50.31.209.229"
Also you can install dnsmasq to the host machine, by the command:
sudo apt-get install dnsmasq
And then you need to add the file /etc/docker/daemon.json with content:
{
"dns": ["host_ip_address", "8.8.8.8"],
}
After that, you need to restart the Docker service by command sudo service docker restart
This option forces to use the host DNS options for every Docker container.
Or you can use it for a single container, and the command-line options are explained by this link. Also docker-compose options are supported (you can read about it by this link).
If you are using docker-compose.yml, the corresponding property is:
services:
xxx:
network_mode: "host"
Source
Add this to your run command:
-v /etc/hosts:/etc/hosts
If trusted users start your containers, you could use a shell function to easily "copy" the /etc/hosts entries that you need:
add_host_opt() { awk "/\\<${1}\\>/ {print \"--add-host $1:\" \$1}" /etc/hosts; }
You can then do:
docker run $(add_host_opt host.name) ubuntu cat /etc/hosts
That way you do not have to hard-code the IP addresses.
The host machine's /etc/hosts file can't mount into a container. But you can mount a folder into the container. And you need a dnsmasq container.
A new folder on host machine
mkdir -p ~/new_hosts/
ln /etc/hosts ~/new_hosts/hosts
mount the ~/new_hosts/ into container
docker run -it -v ~/new_hosts/:/new_hosts centos /bin/bash
Config dnsmasq use /new_hosts/hosts to resolve name.
Change your container's DNS server. Use the dnsmasq container's IP address.
If you change the /etc/hosts file on the host machine, the dnsmasq container's /new_hosts/hosts will change.
I found a problem:
The file in dnsmasq container /new_hosts/hosts can change. But the new hosts can't resolve. Because dnsmasq use inotify listen change event. When you modify a file on the host machine. The dnsmasq can't receive the signal so it doesn't update the configuration. So you may need to write a daemon process to read the /new_hosts/hosts file content to another file every time. And change the dnsmasq configuration to use the new file.
I had the same problem and found that it is likely in contrast with the containerization concept! however I solved my problem by adding each (ip host) pair from /etc/hosts to an existing running container in this way:
docker stop your-container-name
systemctl stop docker
vi /var/lib/docker/containers/*your-container-ID*/hostconfig.json
find ExtraHosts in text and add or replace null with
"ExtraHosts":["your.domain-name.com":"it.s.ip.addr"]
systemctl start docker
docker start your-container-name
if you can stop your container and re-run it, you'd have better situation, so just do that. But if you do not want to destroy your containers, just like mine, it would be a good solution.
If you are running a virtual machine for running Docker containers, if there are hosts (VMs, etc.) you want your containers to be aware of, depending on what VM software you are using, you will have to ensure that there are entries on the host machine (hosting the VM) for whatever machines you want the containers to be able to resolve.
This is because the VM and its containers will have the IP address of the host machine (of the VMs) in their resolv.conf file.
IMO, passing --network=host option while running Docker is a better option as suggested by d3ming over other options as suggested by other answers:
Any change in the host's /etc/hosts file is immediately available to the container, which is what probably you want if you have such a requirement at the first place.
It's probably not a good idea to use the -v option to mount the host's /etc/hosts filr as any unintended change by the container will spoil the host's configuration.
I'm running under boot2docker 1.3.1.
I have a Docker container running a web server via uwsgi --http :8080.
If I attach to the container I can browse the web site using lynx http://127.0.0.1:8080 so I know the server is working.
I ran my container with:
$ docker run -itP --expose 8080 uwsgi_app:0.2
It has the following details:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
5248ad86596d uwsgi_app:0.2 "bash" 11 minutes ago Up 11 minutes 0.0.0.0:49159->8080/tcp cocky_hypatia
$ docker inspect --format '{{ .NetworkSettings.IPAddress }}' 5248ad86596d
172.17.0.107
I thought I could access that web site from my host by going to http://172.17.0.107:49159.
This does not work. I just see 'connecting...' in Chrome, getting nowhere.
What am I doing wrong?
Extending Anentropic's answer: boot2docker is the old app for Mac and Windows, docker-machine is the new one.
Firstly, list your machines:
$ docker-machine ls
NAME ACTIVE DRIVER STATE URL SWARM
default * virtualbox Running tcp://192.168.99.100:2376
Then select one of the machines (the default one is called default) and:
$ docker-machine ip default
192.168.99.100
Ok, stupid me, I found the answer in the docs for boot2docker
https://docs.docker.com/installation/mac/#container-port-redirection
I needed to use the ip address of the boot2docker vm, rather than the ip of the container, i.e.
$ boot2docker ip
192.168.59.103
and I am able to browse my site from the host at http://192.168.59.103:49159/
I did not need to add any route on the host
To find the IP address of your container, you should need NO additional installs:
docker inspect <container>
This provides a wealth of info. grep it for the IPAddress.
You could use boot2docker port mapping option -L, as described here.
So, in your case it would be
boot2docker ssh -L 0.0.0.0:8080:localhost:8080
and then
docker run -it -p 8080:8080 uwsgi_app:0.2
That way, you do not have to use boot2docker's IP address: you can use localhost or your own IP address (and your docker container can be accessed from outside).
Boot2docker is outdated, but you may still have this problem on Docker for Windows or Mac, even though the same container works on Linux. One symptom is that trying to access a page on the server inside the container gives the error "didn't send any data" as opposed to "could not connect."
If so, it may be because on Win/Mac the container host has its own IP, it's not localhost as it is on linux. Try running Django on IP 0.0.0.0, meaning accept connections from all IPs, like this:
python manage.py runserver 0.0.0.0:8000
Alternatively, if you need to make sure the server only responds to local requests (such as from your local proxy like nginx, apache, or gunicorn) you can use the host IP returned by hostname -i.
And make sure you are using the -p port forwarding option correctly in the docker run command.
Assuming all is well, you should be able to access your server at http://localhost in a browser running on the host machine.
docker build -t {imagename} .
docker build -t api-rest-test .
docker run -dp {localport}:{exposeport} image:name
docker run -dp 8080:8080 api-rest-test:latest
make sure you are using the same port for yourlocalport and exposeport
then you can access your rest service in your local machine http://localhost:8080
[EDIT: original version was ignoring the -P in question]
If you want to get to the containers without having to 'publish' the port (which changes its number)
there is a good run-through here.
The key is this line:
sudo route -n add 172.17.0.0/16 172.16.0.11
which tells the Mac how to route to the private network inside the VirtualBox VM that the Docker containers are on.
Had the same issue and in my case i was using AWS EC2 instance. I was trying with the container IP which did not work. Then I used the actual public IP of the AWS host as the IP, which worked.
How to troubleshoot the issue on hosting application on local host browser
For this launch the container with below command, in my case it was:
[root#centoslab3 ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1b81d8a0e3e1 centos:baseweb "/bin/bash" 8 minutes ago Exited (0) 24 seconds ago webtest
[root#centoslab3 ~]# docker run --name=atul -v /root/dockertest:/var/www/html -i -t -p 5000:8000 centos:baseweb /bin/bash
In the httpd configuration:
[root#adb28b08c9ed /]# cd /etc/httpd/conf
[root#adb28b08c9ed conf]# ll
total 52
-rw-r--r--. 1 root root 34419 Sep 19 15:16 httpd.conf
edit the file with the port 8000 in listner and update the container ip and port under Servername.
Restart the httpd service and you are done.
Hope this helps
This question already has answers here:
From inside of a Docker container, how do I connect to the localhost of the machine?
(41 answers)
Closed 10 months ago.
As the title says, I need to be able to retrieve the IP address the docker hosts and the portmaps from the host to the container, and doing that inside of the container.
/sbin/ip route|awk '/default/ { print $3 }'
As #MichaelNeale noticed, there is no sense to use this method in Dockerfile (except when we need this IP during build time only), because this IP will be hardcoded during build time.
As of version 18.03, you can use host.docker.internal as the host's IP.
Works in Docker for Mac, Docker for Windows, and perhaps other platforms as well.
This is an update from the Mac-specific docker.for.mac.localhost, available since version 17.06, and docker.for.mac.host.internal, available since version 17.12, which may also still work on that platform.
Note, as in the Mac and Windows documentation, this is for development purposes only.
For example, I have environment variables set on my host:
MONGO_SERVER=host.docker.internal
In my docker-compose.yml file, I have this:
version: '3'
services:
api:
build: ./api
volumes:
- ./api:/usr/src/app:ro
ports:
- "8000"
environment:
- MONGO_SERVER
command: /usr/local/bin/gunicorn -c /usr/src/app/gunicorn_config.py -w 1 -b :8000 wsgi
Update: On Docker for Mac, as of version 18.03, you can use host.docker.internal as the host's IP. See aljabear's answer. For prior versions of Docker for Mac the following answer may still be useful:
On Docker for Mac the docker0 bridge does not exist, so other answers here may not work. All outgoing traffic however, is routed through your parent host, so as long as you try to connect to an IP it recognizes as itself (and the docker container doesn't think is itself) you should be able to connect. For example if you run this from the parent machine run:
ipconfig getifaddr en0
This should show you the IP of your Mac on its current network and your docker container should be able to connect to this address as well. This is of course a pain if this IP address ever changes, but you can add a custom loopback IP to your Mac that the container doesn't think is itself by doing something like this on the parent machine:
sudo ifconfig lo0 alias 192.168.46.49
You can then test the connection from within the docker container with telnet. In my case I wanted to connect to a remote xdebug server:
telnet 192.168.46.49 9000
Now when traffic comes into your Mac addressed for 192.168.46.49 (and all the traffic leaving your container does go through your Mac) your Mac will assume that IP is itself. When you are finish using this IP, you can remove the loopback alias like this:
sudo ifconfig lo0 -alias 192.168.46.49
One thing to be careful about is that the docker container won't send traffic to the parent host if it thinks the traffic's destination is itself. So check the loopback interface inside the container if you have trouble:
sudo ip addr show lo
In my case, this showed inet 127.0.0.1/8 which means I couldn't use any IPs in the 127.* range. That's why I used 192.168.* in the example above. Make sure the IP you use doesn't conflict with something on your own network.
AFAIK, in the case of Docker for Linux (standard distribution), the IP address of the host will always be 172.17.0.1 (on the main network of docker, see comments to learn more).
The easiest way to get it is via ifconfig (interface docker0) from the host:
ifconfig
From inside a docker, the following command from a docker: ip -4 route show default | cut -d" " -f3
You can run it quickly in a docker with the following command line:
# 1. Run an ubuntu docker
# 2. Updates dependencies (quietly)
# 3. Install ip package (quietly)
# 4. Shows (nicely) the ip of the host
# 5. Removes the docker (thanks to `--rm` arg)
docker run -it --rm ubuntu:22.04 bash -c "apt-get update > /dev/null && apt-get install iproute2 -y > /dev/null && ip -4 route show default | cut -d' ' -f3"
For those running Docker in AWS, the instance meta-data for the host is still available from inside the container.
curl http://169.254.169.254/latest/meta-data/local-ipv4
For example:
$ docker run alpine /bin/sh -c "apk update ; apk add curl ; curl -s http://169.254.169.254/latest/meta-data/local-ipv4 ; echo"
fetch http://dl-cdn.alpinelinux.org/alpine/v3.3/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.3/community/x86_64/APKINDEX.tar.gz
v3.3.1-119-gb247c0a [http://dl-cdn.alpinelinux.org/alpine/v3.3/main]
v3.3.1-59-g48b0368 [http://dl-cdn.alpinelinux.org/alpine/v3.3/community]
OK: 5855 distinct packages available
(1/4) Installing openssl (1.0.2g-r0)
(2/4) Installing ca-certificates (20160104-r2)
(3/4) Installing libssh2 (1.6.0-r1)
(4/4) Installing curl (7.47.0-r0)
Executing busybox-1.24.1-r7.trigger
Executing ca-certificates-20160104-r2.trigger
OK: 7 MiB in 15 packages
172.31.27.238
$ ifconfig eth0 | grep -oP 'inet addr:\K\S+'
172.31.27.238
The only way is passing the host information as environment when you create a container
run --env <key>=<value>
The --add-host could be a more cleaner solution (but without the port part, only the host can be handled with this solution). So, in your docker run command, do something like:
docker run --add-host dockerhost:`/sbin/ip route|awk '/default/ { print $3}'` [my container]
(From https://stackoverflow.com/a/26864854/127400 )
docker network inspect bridge -f '{{range .IPAM.Config}}{{.Gateway}}{{end}}'
It's possible to retrieve it using docker network inspect
The standard best practice for most apps looking to do this automatically is: you don't. Instead you have the person running the container inject an external hostname/ip address as configuration, e.g. as an environment variable or config file. Allowing the user to inject this gives you the most portable design.
Why would this be so difficult? Because containers will, by design, isolate the application from the host environment. The network is namespaced to just that container by default, and details of the host are protected from the process running inside the container which may not be fully trusted.
There are different options depending on your specific situation:
If your container is running with host networking, then you can look at the routing table on the host directly to see the default route out. From this question the following works for me e.g.:
ip route get 1 | sed -n 's/^.*src \([0-9.]*\) .*$/\1/p'
An example showing this with host networking in a container looks like:
docker run --rm --net host busybox /bin/sh -c \
"ip route get 1 | sed -n 's/^.*src \([0-9.]*\) .*$/\1/p'"
For current versions of Docker Desktop, they injected a DNS entry into the embedded VM:
getent hosts host.docker.internal | awk '{print $1}'
With the 20.10 release, the host.docker.internal alias can also work on Linux if you run your containers with an extra option:
docker run --add-host host.docker.internal:host-gateway ...
If you are running in a cloud environment, you can check the metadata service from the cloud provider, e.g. the AWS one:
curl http://169.254.169.254/latest/meta-data/local-ipv4
If you want your external/internet address, you can query a remote service like:
curl ifconfig.co
Each of these have limitations and only work in specific scenarios. The most portable option is still to run your container with the IP address injected as a configuration, e.g. here's an option running the earlier ip command on the host and injecting it as an environment variable:
export HOST_IP=$(ip route get 1 | sed -n 's/^.*src \([0-9.]*\) .*$/\1/p')
docker run --rm -e HOST_IP busybox printenv HOST_IP
TLDR for Mac and Windows
docker run -it --rm alpine nslookup host.docker.internal
... prints the host's IP address ...
nslookup: can't resolve '(null)': Name does not resolve
Name: host.docker.internal
Address 1: 192.168.65.2
Details
On Mac and Windows, you can use the special DNS name host.docker.internal.
The host has a changing IP address (or none if you have no network access). From 18.03 onwards our recommendation is to connect to the special DNS name host.docker.internal, which resolves to the internal IP address used by the host. This is for development purpose and will not work in a production environment outside of Docker Desktop for Mac.
If you want real IP address (not a bridge IP) on Windows and you have docker 18.03 (or more recent) do the following:
Run bash on container from host where image name is nginx (works on Alpine Linux distribution):
docker run -it nginx /bin/ash
Then run inside container
/ # nslookup host.docker.internal
Name: host.docker.internal
Address 1: 192.168.65.2
192.168.65.2 is the host's IP - not the bridge IP like in spinus accepted answer.
I am using here host.docker.internal:
The host has a changing IP address (or none if you have no network access). From 18.03 onwards our recommendation is to connect to the special DNS name host.docker.internal, which resolves to the internal IP address used by the host. This is for development purpose and will not work in a production environment outside of Docker for Windows.
In linux you can run
HOST_IP=`hostname -I | awk '{print $1}'`
In macOS your host machine is not the Docker host. Docker will install it's host OS in VirtualBox.
HOST_IP=`docker run busybox ping -c 1 docker.for.mac.localhost | awk 'FNR==2 {print $4}' | sed s'/.$//'`
I have Ubuntu 16.03. For me
docker run --add-host dockerhost:`/sbin/ip route|awk '/default/ { print $3}'` [image]
does NOT work (wrong ip was generating)
My working solution was that:
docker run --add-host dockerhost:`docker network inspect --format='{{range .IPAM.Config}}{{.Gateway}}{{end}}' bridge` [image]
Docker for Mac
I want to connect from a container to a service on the host
The host has a changing IP address (or none if you have no network access). From 18.03 onwards our recommendation is to connect to the special DNS name host.docker.internal, which resolves to the internal IP address used by the host.
The gateway is also reachable as gateway.docker.internal.
https://docs.docker.com/docker-for-mac/networking/#use-cases-and-workarounds
If you enabled the docker remote API (via -Htcp://0.0.0.0:4243 for instance) and know the host machine's hostname or IP address this can be done with a lot of bash.
Within my container's user's bashrc:
export hostIP=$(ip r | awk '/default/{print $3}')
export containerID=$(awk -F/ '/docker/{print $NF;exit;}' /proc/self/cgroup)
export proxyPort=$(
curl -s http://$hostIP:4243/containers/$containerID/json |
node -pe 'JSON.parse(require("fs").readFileSync("/dev/stdin").toString()).NetworkSettings.Ports["DESIRED_PORT/tcp"][0].HostPort'
)
The second line grabs the container ID from your local /proc/self/cgroup file.
Third line curls out to the host machine (assuming you're using 4243 as docker's port) then uses node to parse the returned JSON for the DESIRED_PORT.
My solution:
docker run --net=host
then in docker container:
hostname -I | awk '{print $1}'
Here is another option for those running Docker in AWS. This option avoids having using apk to add the curl package and saves the precious 7mb of space. Use the built-in wget (part of the monolithic BusyBox binary):
wget -q -O - http://169.254.169.254/latest/meta-data/local-ipv4
use hostname -I command on the terminal
Try this:
docker run --rm -i --net=host alpine ifconfig
So... if you are running your containers using a Rancher server, Rancher v1.6 (not sure if 2.0 has this) containers have access to http://rancher-metadata/ which has a lot of useful information.
From inside the container the IP address can be found here:
curl http://rancher-metadata/latest/self/host/agent_ip
For more details see:
https://rancher.com/docs/rancher/v1.6/en/rancher-services/metadata-service/
This is a minimalistic implementation in Node.js for who is running the host on AWS EC2 instances, using the afore mentioned EC2 Metadata instance
const cp = require('child_process');
const ec2 = function (callback) {
const URL = 'http://169.254.169.254/latest/meta-data/local-ipv4';
// we make it silent and timeout to 1 sec
const args = [URL, '-s', '--max-time', '1'];
const opts = {};
cp.execFile('curl', args, opts, (error, stdout) => {
if (error) return callback(new Error('ec2 ip error'));
else return callback(null, stdout);
})
.on('error', (error) => callback(new Error('ec2 ip error')));
}//ec2
and used as
ec2(function(err, ip) {
if(err) console.log(err)
else console.log(ip);
})
If you are running a Windows container on a Service Fabric cluster, the host's IP address is available via the environment variable Fabric_NodeIPOrFQDN. Service Fabric environment variables
Here is how I do it. In this case, it adds a hosts entry into /etc/hosts within the docker image pointing taurus-host to my local machine IP: :
TAURUS_HOST=`ipconfig getifaddr en0`
docker run -it --rm -e MY_ENVIRONMENT='local' --add-host "taurus-host:${TAURUS_HOST}" ...
Then, from within Docker container, script can use host name taurus-host to get out to my local machine which hosts the docker container.
Maybe the container I've created is useful as well https://github.com/qoomon/docker-host
You can simply use container name dns to access host system e.g. curl http://dockerhost:9200, so no need to hassle with any IP address.
The solution I use is based on a "server" that returns the external address of the Docker host when it receives a http request.
On the "server":
1) Start jwilder/nginx-proxy
# docker run -d -p <external server port>:80 -v /var/run/docker.sock:/tmp/docker.sock:ro jwilder/nginx-proxy
2) Start ipify container
# docker run -e VIRTUAL_HOST=<external server name/address> --detach --name ipify osixia/ipify-api:0.1.0
Now when a container sends a http request to the server, e.g.
# curl http://<external server name/address>:<external server port>
the IP address of the Docker host is returned by ipify via http header "X-Forwarded-For"
Example (ipify server has name "ipify.example.com" and runs on port 80, docker host has IP 10.20.30.40):
# docker run -d -p 80:80 -v /var/run/docker.sock:/tmp/docker.sock:ro jwilder/nginx-proxy
# docker run -e VIRTUAL_HOST=ipify.example.com --detach --name ipify osixia/ipify-api:0.1.0
Inside the container you can now call:
# curl http://ipify.example.com
10.20.30.40
On Ubuntu, hostname command can be used with the following options:
-i, --ip-address addresses for the host name
-I, --all-ip-addresses all addresses for the host
For example:
$ hostname -i
172.17.0.2
To assign to the variable, the following one-liner can be used:
IP=$(hostname -i)
Another approach is based on traceroute and it's working on a Linux host for me, e.g. in a container based on Alpine:
traceroute -n 8.8.8.8 -m 4 -w 1 | awk '$1~/\d/&&$2!~/^172\./{print$2}' | head -1
It takes a moment, but lists the first hop's IP that does not start with 172. If there is no successful response, try increasing the limit on the tested hops using -m 4 argument.
With https://docs.docker.com/machine/install-machine/
a) $ docker-machine ip
b) Get the IP address of one or more machines.
$ docker-machine ip host_name
$ docker-machine ip host_name1 host_name2