Docker Cookbook

3.1 Finding the IP Address of a Container
Problem
You have started a container and would like to find its IP address.
Solution
There are many ways to find the IP address of a container started with the default
Docker networking. This recipe presents a few of them.
70 | Chapter 3: Docker Networking

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The first method is to use the 
docker inspect
 command (see 
Recipe 9.1
 for details)
and the Go template format:
$ docker run -d --name nginx nginx
$ docker inspect --format '{{ .NetworkSettings.IPAddress }}' nginx
172.17.0.2
You can also use the 
docker exec
command and check the IP address by using a
command that executes within the container:
$ docker exec -ti nginx ip add | grep global
inet 172.17.0.2/16 scope global eth0
You could also check the 
/etc/hosts
file in the container, assuming the image does set it
properly:
$ docker run -d --name foobar -h foobar busybox sleep 300
$ docker exec -ti foobar cat /etc/hosts | grep foobar
172.17.0.4 
foobar
Finally, you can enter a shell in the container and issue standard Linux commands at
the prompt:
$ docker exec -ti nginx bash
root@a3c1f7edb00a:/# cat /etc/hosts
See Also
• To understand how Docker networking works and go beyond finding a container
IP address, see 
Recipe 3.4
• 10 
examples
of how to get a Docker container IP address
3.2 Exposing a Container Port on the Host
Problem
You want to access a service running in a container over the network.
Solution
Docker can dynamically map a network port in a container to a port on the host by
using the 
-P
option of 
docker run
. You can also manually specify a mapping by using
the 
-p
option.
Let’s say that you have built an image that runs a Python Flask application using the
Dockerfile shown here: