DecisionDefine the order of steps when building a Drupal site

Decision

This ADR has been replaced by this new version.

We standardize the build steps as:

vendor/bin/drush cache:clear plugin -y
# Run numbered module updates (hook_update_N) only.
vendor/bin/drush updatedb --no-post-updates -y
# Run config:import twice to make sure we catch any config that didn't declare
# a dependency correctly. This is also useful when importing large config sets
# as it can sometimes hit an out of memory error.
vendor/bin/drush config:import -y || true
vendor/bin/drush config:import -y
# Run updatedb again for updates dependent on config changes
# This second run should fire all hook_post_update_NAME() hooks.
vendor/bin/drush updatedb --no-cache-clear -y
vendor/bin/drush cache:rebuild -y

Developers should write update hooks using these guidelines:

HOOK_update_N()

Code that does not rely on any Drupal APIs, usually to perform direct database queries.

These hooks are the first ones to be executed, before configuration is imported.

HOOK_post_update_NAME()

These are called when Drupal is fully bootstrapped and all Drupal APIs are safe to use.

Using the approach outlined above with two drush updatedb executions, implementations of this hook will be executed after configuration is imported, so developers are able to rely on new config being available when it's executed.

Limitations

At time of writing, there is at least one scenario where the steps above could cause issues in deployments. When a deployment includes a module being enabled (through config changes in core.extension.yml) and it has a weight different than 0, the detection of post_update hooks in the second execution of drush updatedb doesn't work.

When using the order of operations described in this ADR, try to avoid deployments that contain new modules with weight greater than 0 and post_update hooks, even if these hooks are implemented in unrelated modules.

Consequences

• Developers have a clear and consistent guide to use update hooks among projects.
• Automation can be built to ensure these steps are executed consistently.