Moving a WordPress site into a Docker Container

WordPress is a very popular and flexible Content Management System (CMS). If you build websites, you are likely to have worked with (or had someone ask you to) WordPress.

There are several tutorials about how to set up a new WordPress site with docker. Here is a very good one. However, no one really says how to move an existing WordPress site into a docker container.

I have several servers on Digital Ocean, Linode and Vultr, and I decided to move a couple of my sites, including this one, from a shared server, into docker containers on my servers.

Here is my usual process.

Things to note

1. I will be using _example.com_as the domain in this article.
2. I will use 12.34.56.78 as the IP address of the server.
3. I am working with an Ubuntu 16.04 server.

Prerequisites

Install Nginx on the server. We’ll use Nginx as a reverse proxy for our docker container, so we have to install it using the following command.

sudo apt install nginx

Step 1: Understanding Docker Compose

In the last post, we used the direct docker --run command but since we’ll be dealing with more than one container, it’ll be much easier to work with docker-compose.

Docker compose is a tool used to configure several containers at once. From the official documentation

Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a Compose file to configure your application’s services. Then, using a single command, you create and start all the services from your configuration.

To update (or install) your docker version to the latest one and install docker-compose, you can run the following command.

wget -O - https://bit.ly/docker-install| bash

With docker-compose, we will define a single docker-compose.yml file for our entire stack.

Step 2: Export the WordPress site

Before you start moving your WordPress site, it is usually a good idea to deactivate all plugins first.

We need the following things from the current site.

1. A zip archive of the entire contents of the WordPress site. (I’ll refer to this as site.zip)
2. A dump of the MySQL database. (I’ll refer to this as database.sql)
3. The database name. (I’ll refer to this as example_db_name)
4. The database password. (I’ll refer to this as example_db_password)
5. The database user. (I’ll refer to this as example_db_user)

Once you have them, place them in the root of your current site. i.e example.com/database.sql and example.com/site.zip.

Step 3: Set up the site source code

Make sure the /var/www/example.com folder is empty, then create an src/ folder inside it to contain our site code. You can do both of those with the following commands

rm -r /var/www/example.com/*
mkdir -pv /var/www/example.com/src

Now we will download the site archive we created to our site.

cd /var/www/example.com
wget "http://example.com/site.zip" --no-check-certificate

Next we will unzip the site.zip archive into the src folder

unzip site.zip -d src/

Now, we should have our WordPress site code fully copied to our server

Step 4: Set up the site database

WordPress requires a database to work, and since we want to keep our data, we’ll store the data in a directory volume which we will mount unto our docker container.

Next, we’ll create the folder /var/www/example.com/database to contain our database data and configuration.

mkdir -pv /var/www/example.com/database

We will store our database data inside the database/data folder, so we create it using the following command

mkdir -pv /var/www/example.com/database/data

The MySQL container will execute any .sh, .sql or .sql.gz file in the /docker-entrypoint-initdb.d folder inside the container. So, we will place our sql dump into a folder and mount that into the /docker-entrypoint-initdb.d folder of the container.

mkdir -pv /var/www/example.com/database/initdb.d
cd /var/www/example.com/database/initdb.d
wget "http://example.com/database.sql" --no-check-certificate

Step 5: Start Docker containers using docker-compose

We will be using the official WordPress docker image to hold our code, and the official MySQL image for our database. To prepare the docker-compose, we’ll need to create a docker-compose.yml file

Now, we’ll create the docker-compose.yml file.

touch /var/www/example.com/docker-compose.yml

Edit docker-compose.yml and add the following

version: '2'

services:
  example_db:
    image: mysql:5.7
    container_name: example_db
    volumes:
      - ./database/data:/var/lib/mysql
      - ./database/initdb.d:/docker-entrypoint-initdb.d
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: aieububsnlVUOBWHLEINA # any random string will do
      MYSQL_DATABASE: example_db_name # the name of your mysql database
      MYSQL_USER: example_db_user # the name of the database user
      MYSQL_PASSWORD: example_db_password # the password of the mysql user

  example:
    depends_on:
      - example_db
    image: wordpress:php7.1 # we're using the image with php7.1 
    container_name: example
    ports:
      - "1234:80"
    restart: always
    links:
      - example_db:mysql
    volumes:
      - ./src:/var/www/html

We will bring up our docker containers using the docker-compose command.

To keep our site data safe, we will add Docker Volumes to the example and example_db services.  This means that if we decide to take the container down, our site and data won’t be deleted.

cd /var/www/example.com
docker-compose up -d

Step 6: Use Nginx as a reverse proxy to our Docker Container

Our Docker container is now running, but our site is not up just yet. Let us set up our Nginx configuration file for our website to serve content from within our docker container.

cd /etc/nginx/sites-available
touch example.com.conf

Now edit example.com and make it look like this.

server {
    listen 80;
    listen [::]:80;

    server_name example.com www.example.com;
    location / {
        proxy_pass http://0.0.0.0:1234;
        proxy_set_header Accept-Encoding "";
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Enable the site config so Nginx can load it

ln -s /etc/nginx/sites-available/example.com.conf /etc/nginx/sites-enabled/example.com.conf

Reload Nginx for our configuration to take effect.

/etc/init.d/nginx reload

Step 7: Fix wp-config.php

If you try to visit the site now, you’ll most likely see a database error. To fix this, edit the wp-config file at /var/www/example.com/src/wp-config.php and change

/** MySQL hostname */
define('DB_HOST', 'localhost');

to

/** MySQL hostname */
define('DB_HOST', 'mysql');

Also, just above /* That's all, stop editing! Happy blogging. */, add the following

if (isset($_SERVER['HTTP_X_FORWARDED_PROTO']) 
    && $_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https') {
    $_SERVER['HTTPS'] = 'on';
}

Congratulations! You should be able to visit your site and see everything working properly.

Step 8: Install a free SSL certificate and use HTTPS (Optional)

To do this, follow step 4 to 7 of my last post.

Feel free to ask any questions, and leave comments of how this went for you.