How to get the IP address of the docker host from inside a docker container

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

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.

Answer 2

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

Answer 3

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

Answer 4

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

Answer 5

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 6

Try this:

docker run --rm -i --net=host alpine ifconfig