How to get the IP address of the docker host from

Question

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.

Answer 1

On Docker for Mac, as of version 18.03, you can use host.docker.internal as the host's IP.

Note, as in the documentation, "This is for development purpose[s] and will not work in a production environment outside of Docker for Mac." This is because, in Docker for Mac, "you cannot see a docker0 interface on the host. This interface is actually within the virtual machine."

This is an update from 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.

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

Answer 2

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

Answer 3

Update: On Docker for Mac, as of version 18.03, you can use host.docker.internal as the host's IP. See allanberry'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.

Answer 4

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.

Answer 5

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

Answer 6

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.