Configuration management in Drupal 8/9

Drupal 8/9 allows configuration to be imported into a database or exported to disk as yml files.

A common configuration management workflow is based on the Configuration split module, described in Managing Configuration with Config Split. For most projects, configuration split strikes the balance of flexibility, reliability, and ease of maintenance and development.

General principles

The following section describes aspects of the development and deployment process common to all CM workflows.

Basics of configuration management

The primary goal of configuration management is to ensure you can review, test, and predictably deploy all configuration changes to production environments. Some easy changes, such as changing a website s name or slogan, can have limited, atomic, and predictable effects, and not require strict change management. Other types of changes, such as modifying field storage schemas, always must go through a review process. Different projects can have different degrees of risk tolerance. For instance, some can prefer configuration be strictly read-only in production, prohibiting even the easy website name change.

A good CM workflow must be flexible enough to handle either of the preceding use cases. A CM workflow must make it easy for developers to make, and capture configuration changes, review, and test the changes, and reliably deploy the changes to a remote environment.

A configuration change follows the following lifecycle:

• A developer makes the change in their local environment.
• The developer uses CM commands to export the configuration change to disk.
• The developer commits the new or updated configuration to VCS and opens a pull request.
• Automated testing ensures the configuration can be installed from scratch on a new website and imported without conflicts on an existing website.
• After you deploy the change, deployment hooks automate the import of the new or updated configuration.

Configuration is captured and deployed between environments in Drupal typically through YAML files. The YAML files, stored in a root config directory, or distributed with individual modules in config/install directories, represent individual configuration objects synchronized with the active configuration in an environment s database by several methods. For more information, see the documentation about core configuration management on Drupal.org.

The following documentation addresses the challenge of capturing (exporting), and deploying (importing) configuration in a consistent way to support the workflow already described.

Configuration versus content

You can't use Drupal's configuration system to manage entities Drupal considers to be content, such as nodes, taxonomy terms, and files. This can create conflicts when a configuration entity depends on a content entity, such as:

• You have a block type including a file upload field, and you want to place the block in a theme and export the block configuration.
• You have a view filtered by a static taxonomy term, and you want to export the view configuration.

In such cases, the exported configuration file for the block or view will define a dependency on a content object (referenced by UUID). If the content doesn't exist when you import the configuration, the import will fail.

The solution is to ensure the referenced content exists before you import the configuration. Two recommended methods include:

• Use the Default Content module to export the referenced content as JSON files, and store the files with a feature or other dedicated module.
• Use Migrate and a custom module to create default content from any number of custom sources, such as JSON files stored with your feature.

Updating core and contributed modules

Use caution updating core and contributed modules when using any sort of configuration management process. If those updates make changes to a module's configuration or schema, you must ensure you update your exported configurations. Otherwise, the next time you import the configuration (such as on deploys), the import of your configuration will overwrite changes made by the database updates. Your database and codebase will become out of sync.

The best way to prevent such problems is to always use the following steps when updating contributed and core modules. The steps assume you are using configuration split or a similar CM strategy using drush cex and drush cim:

• Start from a clean install or database sync, including config import (blt setup or blt drupal:sync). Ensure that your active and exported configuration are in sync (running drush config-export must report no changes).

• Use composer update or composer update drupal/[module_name] --with-dependencies to download the new module version(s). To update Drupal core, use the following command:

  copy

  composer update webflo/drupal-core-require-dev drupal/core --with-dependencies

• Run the following command to apply any pending updates locally:

  copy

  drush updb

• Export any changed configuration as part of the database updates or new module versions by running drush config-export and determining if there are any changes on disk by running git status.
• Commit any changed configuration, along with the updated composer.json and composer.lock files.

Acquia is working on a better way of preventing the codebase and database from becoming out of sync other than manually monitoring module updates. Find more information on these issues at Features and contributed module updates, and Testing for schema changes to stored configuration.

Ensuring the integrity of stored configuration

Configuration stored on disk is essentially a flat-file database and must be treated as such. For instance, you must make all changes to configuration through the user interface, through an appropriate API, and then export to disk. You must never make changes to individual configuration files by hand, in the same way you must never write a raw SQL query to add a Drupal content type. Even seemingly small changes to one part of the configuration can have sweeping and unanticipated changes. For instance, enabling the Panelizer or Workbench modules will change the configuration of every content type on the website.

Acquia BLT has a built-in test helping to protect against some of these mistakes. After you import the configuration such as during drupal:update or artifact:update:drupal, the tests will check if any configuration remains overridden. If so, the build will fail, alerting you to un-captured configuration changes or a corrupt configuration export. The test assists in monitoring and must not be disabled, but if you must temporarily disable it in an emergency such as if deploys to a cloud environment are failing, you can do so by settings cm.allow-overrides to true.

You must enable protected branches in GitHub to ensure you can only merge pull requests if they are up to date with the target branch. Enabling protected branches guards against where one pull request adds a new content type, while another pull request enables Workbench changing the content type. Individually, each pull request is valid, but once they are both merged, they produce a corrupt configuration where the new content type lacks Workbench configuration.

For an ongoing discussion on ensuring configuration integrity, see https://www.drupal.org/node/2869910.

Using update hooks to import individual config files

If you must import a configuration change before update hooks run, in your hook, you must import the needed configuration from files first. An example would be adding a new taxonomy vocabulary through configuration, and populating the vocabulary with terms in an update hook.

The following code snippet demonstrates importing a taxonomy vocabulary configuration first before creating terms in the vocabulary:

use Drupal\taxonomy\Entity\Term;

// Import taxonomy from config sync directory.
$vid = 'foo_terms'; // foo_terms is the vocabularly id.
$vocab_config_id = "taxonomy.vocabulary.$vid";
$vocab_config_data = foo_read_config_from_sync($vocab_config_id);
\Drupal::service('config.storage')->write($vocab_config_id, $vocab_config_data);

Term::create([
  'name' => 'Foo Term 1',
  'vid' => $vid',
])->save();

Term::create([
  'name' => 'Foo Term 2',
  'vid' => $vid',
])->save();

The preceding code depends on a helper function, which you can add to your custom profile:

use Drupal\Core\Config\FileStorage;

/**
 * Reads a stored config file from config sync directory.
 *
 * @param string $id
 *   The config ID.
 *
 * @return array
 *   The config data.
 */
function foo_read_config_from_sync($id) {
  // Statically cache FileStorage object.
  static $storage;

  if (empty($storage)) {
    global $settings['config_sync_directory'];
    $storage = new FileStorage($settings['config_sync_directory'][CONFIG_SYNC_DIRECTORY]);
  }
  return $storage->read($id);
}