Run Wordpress with docker-compose without using the wordpress image - php

Question

I would like to upgrade a very old wordpress installation. I would like to reproduce the live enviroment locally. For this, I would build my PHP, MySQL via docker compose. However, I have a problem with this. Normally you would take the ready wordpress images for this. But in my case I can't do that because the WP version is not supported in the docker hub or elsewhere. For this reason I would build my docker-compose with the following images: php7.0, apache and MySql. However, I am wondering how to include the PHP modules that wordpress needs in my yaml file. Is there a template I can follow? And is the way I choose here the right one or is there an alternative way?

Answer 1

Docker images are made out of layers. You can take a PHP image from Docker Hub and add onto it. In fact, the official Wordpress image uses the official PHP image as a base.
Create a new Dockerfile.
You can pick a PHP 7 variant as the starting base:
FROM php:7.0-apache
For some extensions, like GD Library (used for making thumbnails) you need to install some dependencies. This image is based on Debian Linux, so you use:
RUN apt-get -y update && apt-get -y install libfreetype6-dev libjpeg62-turbo-dev libpng-dev unzip
Next, you want some PHP extensions like the aforementioned GD Library and MYSQLi. In the official PHP image, there's a utility (see "How to install more PHP extensions") that makes it very simple:
RUN docker-php-ext-configure gd --with-freetype --with-jpeg
RUN docker-php-ext-install mysqli gd exif zip
Now you can build your image:
docker build -t mycustomphpimage:latest .
And run it:
docker run mycustomphpimage:latest
Building the image automatically with CI/CD in Gitlab/Github and deploying custom images to a repository to pull on a server is out of scope for this answer.
You could just build the image on the server itself when deploying. If you don't want to do that, you can also build the image locally and use docker export & docker import.
The Wordpress image for Wordpress installs some extensions, the most critical of these are gd, exif (images), zip (unpacking plugins), mysqli (database). Try to find out what your current production server has installed & add those to the Dockerfile—many will "just work" with docker-php-ext-install and some might be ignorable.
It might also be possible to use an old version of the Wordpress 5.0 image or to use it as a base (FROM wordpress:5-php7.0-apache).
You mentioned that you'd like to do this to upgrade an old install, so the following is not applicable to you, but for the sake of anyone that finds this answer in the future: just because you can run old PHP / Wordpress versions, please don't do that in production and try to upgrade as soon as you can.