Experiments in Assets, and bootstrapping Drupal

[birkland]

Overview

Basically, this PR started as an approach to using an "assets" image for storing local state (drupal add-ons and config, mysql dbs, solr, etc). These experiments revealed a flaw in the recommended approach to "volumizing" local content in Drupal. I observed:

• The recommended mount points for Drupal are /var/www/html/{modules,profiles,sites,themes}
• Drupal presumes content in /var/www/html/sites, which using an assets image provides.
  • In other words, Drupal presumes there is stuff in /var/www/html/sites.
  • Unfortunately, that "stuff" can't be provided by the Drupal image, since /var/www/html/sites is a mounted volume
  • Using the assets image as present in this PR provides initial content for the volume, as provided by a tar file at build time.
    • Look at the contents of the tar file used in this PR: tar -tf build/assets/data/assets.tar.gz. This is the most basic assets content that makes "an empty Drupal work".
• In order to create an initial Drupal site, it's necessary to (1) Create a mysql user with the appropriate permissions, (2) Use Drush to do a site install, (3) Add any necessary modules. I was intending to script this, then create an assets snapshot from the results in order to "bring a Drupal site up quickly with docker-compose up -d.
  • Right now, I have a script bootstrap.sh inside the assets image which can be manually run in order to do this: bootstrap.sh
• Unfortunately, installing a theme and the solr module results in the addition and modification of php files outside of the recommended mount points of /var/www/html/{modules,profiles,sites,themes}. In fact, it looks like anything under /var/www/html is fair game for installation or modification using composer. Thus, I believe /var/www/html itself has to be a mounted volume, as it's all local state
  • I think implies that a Drupal installation itself is "local state" as far as volumes are concerned.
  • I think that also implies that there can be no such thing as a "Drupal image" that provides any initial content under /var/www/html, including Drupal itself

Try it out

This will illustrate the issues above. Check out this PR, and do the following:

• Build the images: docker-compose.exe -f docker-compose.mvp1.yml build
• Start the stack: docker-compose.exe -f docker-compose.mvp1.yml up -d
• At this point, Drupal is running with the sites content in a volume, provided by the assets image. Hop into that container to verify
  • Get a shell in the Drupal container via docker exec -it isle-dc-drupal-idcp bash
  • Do ls -l /var/www/html/sites, you'll see it's a symlink: /var/www/html/sites -> /mnt/assets/sites
  • explore /mnt/assets. This is where the Drupal assets are mounted.
  • Do ls -l /var/www/html/sites/ (note trailing slash). You can see the site files provided by the assets image.
  • Exit out of the shell
• Now, we're going to run a script that creates a mysql user, and installs a drupal site.
  • Run docker exec -i isle-dc-assets-idcp bootstrap.sh. It'll take a couple minutes to finish
• Verify the site works, go to http://localhost:8080. Log in as admin:islandora if you want.
• Ideally, nothing significant in any base image would change in this process. We want all state changes to be in mounted volumes. Unfortunately, that's not the case. Do a docker diff:
  • docker diff isle-dc-drupal-idcp | grep /var/www/html D'OH!
• We can dump assets images into a tar. Unfortunately, because installing Drupal themes and modules added content outside our mount points, the resulting assets image wouldn't capture everything it needs. But we can do it anyway just to see it
  • docker exec -i isle-dc-assets-idcp dump.sh
  • Look at the resulting build/assets/data/assets.tar.gz file in your locak directory. It has a lot more in it, doesn't it
  • If you do a build, Docker will create a new assets image using that newly dumped assets file. These images can be pushed just like regular Docker images, but their distinguishing characteristic is that they seed volumes with whatever content has been baked in them during a docker build, originating from the tar file. This is where the magic lies, IF we get the mount points for Drupal right!