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Deploying WordPress using a Docker network

In this recipe, we will learn to use a Docker network to set up a WordPress server. We will create two containers, one for MySQL and the other for WordPress. Additionally, we will set up a private network for both MySQL and WordPress.

How to do it…

Let's start by creating a separate network for WordPress and the MySQL containers:

A new network can be created with the following command:
```
$ docker network create wpnet
```
Check whether the network has been created successfully with docker network ls:
```
$ docker network ls
```
You can get details of the new network with the docker network inspect command:
```
$ docker network inspect wpnet
```

Next, start a new MySQL container and set it to use wpnet:

$ docker run --name mysql -d \
-e MYSQL_ROOT_PASSWORD=password \
--net wpnet mysql

Now, create a container for WordPress. Make sure the WORDPRESS_DB_HOST argument matches the name given to the MySQL container:

$ docker run --name wordpress -d -p 80:80 \
--net wpnet\
-e WORDPRESS_DB_HOST=mysql\
-e WORDPRESS_DB_PASSWORD=password wordpress

Inspect wpnet again. This time, it should list two containers:

Now, you can access the WordPress installation at your host domain name or IP address.

How it works…

Docker introduced the container networking model (CNM) with Docker version 1.9. CNM enables users to create small, private networks for a group of containers. Now, you can set up a new software-assisted network with a simple docker network create command. The Docker network supports bridge and overlay drivers for networks out of the box. You can use plugins to add other network drivers. The bridge network is a default driver used by a Docker network. It provides a network similar to the default Docker network, whereas an overlay network enables multihost networking for Docker clusters.

This recipe covers the use of a bridge network for wordpress containers. We have created a simple, isolated bridge network using the docker network command. Once the network has been created, you can set containers to use this network with the --net flag to docker run command. If your containers are already running, you can add a new network interface to them with the docker network connect command, as follows:

$ # docker network connect network_name container_name
$ docker network connect wpnet mysql

Similarly, you can use docker network disconnect to disconnect or remove a container from a specific network. Additionally, this network provides an inbuilt discovery feature. With discovery enabled, we can communicate with other containers using their names. We used this feature while connecting the MySQL container to the wordpress container. For the WORDPRESS_DB_HOST parameter, we used the container name rather than the IP address or FQDN.

If you've noticed, we have not mentioned any port mapping for the mysql container. With this new wpnet network, we need not create any port mapping on the MySQL container. The default MySQL port is exposed by the mysql container and the service is accessible only to containers running on the wpnet network. The only port available to the outside world is port 80 from the wordpress container. We can easily hide the WordPress service behind a load balancer and use multiple wordpress containers with just the load balancer exposed to the outside world.

There's more…

Docker also supports links to create secure communication links between two or more containers. You can set up a WordPress site using linked containers as follows:

First, create a mysql container:

$ docker run --name mysql -d \
-e MYSQL_ROOT_PASSWORD=password mysql

Now, create a wordpress container and link it with the mysql container:
```
$ docker run --name wordpress -d -p 80:80 --link mysql:mysql
```
And you are done. All arguments for wordpress, such as DB_HOST and ROOT_PASSWORD, will be taken from the linked mysql container.

The other option to set up WordPress is to set up both WordPress and MySQL in a single container. This needs process management tools such as supervisord to run two or more processes in a single container. Docker allows only one process per container by default.