How to best add extensions when using official docker image for MediaWiki?

Question

We are using the official MediaWiki Docker image and want to be able to add additional MediaWiki extensions.

Questions:

1. What is the recommended next step

Answer 1

As OP suggested, you need to create an image which wraps the official MediaWiki image.

Write instructions to make an image with extra extensions

As a minimal example we'll create an image which includes the EmbedVideo extension, which is not bundled with MediaWiki as of version 1.31. Add the following instructions the file my-mediawiki/Dockerfile:

FROM mediawiki:latest

RUN git clone --depth 1 https://github.com/HydraWiki/mediawiki-embedvideo.git /var/www/html/extensions/EmbedVideo

Build the image

Turn this Dockerfile into an image using docker build:

$ docker build -t username/mediawiki ./my-mediawiki
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM mediawiki:latest
latest: Pulling from library/mediawiki
802b00ed6f79: Pull complete
# [lines omitted]
8b47ece631d8: Pull complete 
Digest: sha256:5922653b254073c6d6a535bbdb0101f8a5eadbf557e2f31d590c234001c55b60
Status: Downloaded newer image for mediawiki:latest
 ---> 27fe73856ca7
Step 2/2 : RUN git clone --depth 1 https://github.com/HydraWiki/mediawiki-embedvideo.git /var/www/html/extensions/EmbedVideo
 ---> Running in 30a411511341
Cloning into '/var/www/html/extensions/EmbedVideo'...
Removing intermediate container 30a411511341
 ---> 5b297228bb08
Successfully built 5b297228bb08
Successfully tagged username/mediawiki:latest

Test the image

Test the image using docker run:

$ docker run --rm -p 8080:80 username/mediawiki

While this container is running visit localhost:8080 with a web browser. You will be asked to perform the setup procedure. When you get to the options page the EmbedVideo extension will be included in the list of extensions.

Perform the rest of setup

Other steps are needed to get MediaWiki running in docker, such as providing a LocalSettings.php file and connecting it to a database. Follow the official MediaWiki Docker documentation for these steps, substituting your username/mediawiki image for the official mediawiki image.

Add additional plugins

Multiple plugins can be installed by appending more RUN instructions to the end of my-mediawiki/Dockerfile. For example, to add Scribunto, append the following to the bottom of the file:

RUN git clone --depth 1 -b $MEDIAWIKI_BRANCH \
      https://gerrit.wikimedia.org/r/p/mediawiki/extensions/Scribunto \
      /var/www/html/extensions/Scribunto \
      && chmod a+x /var/www/html/extensions/Scribunto/includes/engines/LuaStandalone/binaries/lua*_linux_*/lua

After modifying the Dockerfile update the image using:

docker build -t username/mediawiki ./my-mediawiki

Most extensions require you to modify LocalSettings.php, and like Scribunto some will require additional installation commands to be run after download (check each extensions's README). Complex extensions like VisualEditor will require additional containers to run daemons such as Parsoid. My own Dockerfile and docker-compose.yml illustrate how other plugins can be configured.