Docker Network Between Container

We can run multiple container on our host machine using Docker. By default when we run multiple container, one cannot communicate with other. If we want our multiple container to communicate between each other we can use Docker Network.

Docker Network lets you create a isolated network where we can connect our container. Container cannot access external network but if other container are connected to same network they can orchestrate between each other. To create a network is simple as

# docker network create <network_name>
  docker network create anetwork

By default Docker creates network with bridge driver. If you want to create a network with other driver you can use -d option. Default option Docker accepts are bridge and overlay. Bridge networks are isolated networks on a single Engine installation.

We can now add the container in the network we just created.

1. Use --net when we run our docker #

If we want to add our container to network when we execute docker run we can use --net option which accepts the network name. In order for container to orchestrate Docker uses container name so we can use --name option to give name to container.

docker run -d --net=anetwork --name=mysql -e MYSQL_USER=ROOT -e MYSQL_ALLOW_EMPTY_PASSWORD=yes mysql

In above command we are running the mysql container in network anetwork with the name mysql. If other container wants to communicate with mysql they can use container name i.e mysql. Notice we are running our mysql container in deamon mode with -d flag.

Let’s add another container to network

docker run --net=anetwork --name=pythonapp -it python:2.7-wheezy bash

Above command adds pythonapp into the network anetwork. Notice we are starting our pythonapp with -it flag and we are passing bash as argument. When we execute above command we will be interacting pythonapp bash shell.

To check if we can communicate with mysql we can use ping command

ping mysql

2. Use docker network connect #

Above process works perfect if you are running a new container. What if you want to create a network and add already running container to newly created network. That’s where docker network connect comes handy.

Here’s a syntax

docker network connect <network_name> <container_name>

You can see that to add existing container to network we first need a network name and container name.

Assume we have two container with name mysql and pythonapp. Let’s create a network

docker network create anetwork

To add container to network use docker network connect

docker network connect anetwork mysql
docker network connect anetwork pythonapp

That’s it, now two container can communicate with each other.