Drupal 7 to 8 Migration Diary (Part 2): Using Configuration Installer to delay a canonical database

Published 11 June 2016

This post is the second in a series about migrating nerdologues.com from Drupal 7 to Drupal 8. Read the first post here.

The configuration workflow I want to use

When I started on this project to migrate nerdologues.com from Drupal 7 to Drupal 8 I was excited to use Drupal 8’s Configuration Manager. My imagined workflow was something like:

  • Install Drupal 8 with the core’s Standard install profile on my local machine or in a Pantheon Multidev environment.
  • Make configuration changes.
  • Export configuration changes to code (wooo!) to the normal directory: sites/default/config.
  • Push committed configuration to GitHub, make pull request.
  • CircleCI then installs with the Standard profile, imports configuration from sites/default/config, runs tests.

But there is a problem with this workflow. When attempting to do the import of pre-existing configuration (with drush config-import) Drupal will complain with a message that includes:

The import failed due for the following reasons:                         
Site UUID in source storage does not match the target storage.

As far as Drupal core is concerned, sites/default/config is meant for configuration from the same site (or at least different copies of the same site). Doing a fresh install of Drupal core means that the pre-existing config in sites/default/config is seen as foreign.

Enter Configuration Installer

Configuration Installer allows me to use the workflow that I want. (Thanks to Alex Pott for writing it!) Drupal bases new installations on installation profiles. In Drupal 8, each install profile is expected to provide the configuration it needs in the form of .yml files. For most every install profile, those .yml files live inside the directory of the install profile (see the directory structure of core’s Standard and Minimal install profiles). Configuration Installer is a way to say “my install profile configuration is actually over in sites/default/config.” It’s a workaround that works well. Here’s a pull request that updates the permissions for the Content Administrator role’s configuration and changes some Behat tests accordingly.

How are other people working without Configuration Installer?

I would not need Configuration Installer if I established a canonical Drupal 8 database. With a canonical Drupal 8 database, CircleCI would would run on a copy of that D8 database and then import configuration changes rather than installing fresh which creates a new database. Once the Drupal 8 site is live (and has a canonical database), that will be the workflow. But I don’t want to go that workflow yet. A Drupal site has three main parts:

  • Version-controlled code.
  • Files ignored from version control (mostly uploaded images/documents).
  • A database.

Of the three, the database is easiest element to mess up and the hardest to fix after a mistaken change. That’s why Drupal 8 introduced new configuration management tools that move focus from the database to version controlled code. Configuration does still live in the database as far as a runtime Drupal site is concerned but configuration is so cleanly imported and exported to code now that mental focus goes to the .yml files.

In essence, a Drupal-to-Drupal migration is the transitioning from one set of canonical code/files/database to another. I want to minimize the amount of time that I have two canonical databases to worry about. Right now I can think that any pull request I make on my Drupal 8 code can result in the running of a full data migration to a disposable Drupal 8 database. If there is something I don’t like about the Drupal 8 database that is produced by the pull request, I can throw it away and try again. Even if the changes are correct, the Drupal 8 databases are all temporary at this point.

If I did have a canonical Drupal 8 database, it would be running on some tag of my Drupal 8 code’s master branch. I would be much more hesitant to make merges to master out of fear that I might mess up the Drupal 8 canonical database. I will put off that conceptual switch as long as doing so saves me time and mental energy. Especially for a side project, I don’t want to be thinking with every pull request “in what way exactly is this change made more complicated by having two canonical databases?”

Where are the relevant pieces in the project?

(These links are to a specific git hash in my Drupal 8 repo because the relevant code might have moved by the time you are reading this blog post.)

Configuration Installer is letting me work the way I want to work at this point while the Drupal 8 site is in heavy development. After the site is live, I wonder if I will want to remove it to have one fewer dependency. That’s a question for another day, or year.

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