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Configuration management with Acquia BLT

Acquia BLT supports several methods of configuration management (CM) in Drupal 8. All configuration management methods rely to varying degrees on Drupal core’s configuration entities, which can be imported into a database or exported to disk as yml files.

Acquia BLT strongly recommends a CM workflow based on the Configuration split module, described in Managing Configuration with Config Split. For most projects, configuration split strikes the best balance of flexibility, reliability, and ease of maintenance and development. A Features-based workflow (analogous to most CM workflows in Drupal 7) can better handle certain multisite architectures, but has a much greater development and maintenance overhead.

General principles

The following section describes aspects of Acquia BLT’s 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:

  1. A developer makes the change in their local environment.
  2. The developer uses CM commands to export the configuration change to disk.
  3. The developer commits the new or updated configuration to VCS and opens a pull request.
  4. Automated testing ensures the configuration can be installed from scratch on a new website and imported without conflicts on an existing website.
  5. 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 8 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

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

How Acquia BLT handles configuration updates

Acquia BLT-based projects already support the workflow, including automated imports of configuration updates. Acquia BLT defines a generic drupal:update task applying any pending database and configuration updates. The same task can be re-used locally or remotely (through the drupal:update, and artifact:update:drupal wrappers, respectively) to ensure configuration changes and database updates behave identically in all environments.

When you run one of the update commands, they perform the following updates (see drupal:config:import):

  • Database updates: the same as running drush updb or hitting update.php, applying any pending database updates.

  • Configuration import: runs the core configuration-import command to import any configuration stored in the root config directory. The import is either a full or partial import, depending on how you configure Acquia BLT.

  • Features import (optional): runs features-import-all, which imports any configuration stored in a feature module’s config/install directory.


    The features-import-all command only runs if you have configured the cm.features.bundle property in blt/blt.yml.

There are also pre and post-config import hooks you can use to run custom commands.

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. Failing to take the preceding scenario into account is the most common cause of configuration imports failing Acquia BLT’s test for overridden configuration.

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:

  1. 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).

  2. 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:

    composer update webflo/drupal-core-require-dev drupal/core --with-dependencies
  3. Run the following command to apply any pending updates locally:

    drush updb
  4. 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.

  5. 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, whether through the core configuration system or features, 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 uncaptured 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. When used with Acquia BLT’s built-in test for configuration overrides, protected branches can quite effectively prevent some forms of configuration corruption.

For an ongoing discussion on ensuring configuration integrity, see

Configuration split workflow

For detailed information on how you can create and enable configuration splits, see Configuration split and Managing Configuration with Config Split.

If Acquia is not working with the configuration split module, ensure you are using Drush version 8.1.10 or later, Configuration Split version 8.1.0-beta4 or later, and that you configured cm.strategy to config-split in the blt/blt.yml file.

Using update hooks to import individual config files

Acquia BLT runs module update hooks before importing configuration changes. If you must import a configuration change before the update hook runs, 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('')->write($vocab_config_id, $vocab_config_data);

  'name' => 'Foo Term 1',
  'vid' => $vid',

  'name' => 'Foo Term 2',
  'vid' => $vid',

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 $config_directories;
    $storage = new FileStorage($config_directories[CONFIG_SYNC_DIRECTORY]);
  return $storage->read($id);

Features-based workflow

The Features module allows you to bundle related configuration files such as a content type and its fields into individual feature modules. Drupal treats features like normal modules, but Features and its dependencies allow features to provide default configuration and update changes to the configuration.

Due to the modular architecture, Features is a better solution for certain multisite applications where you must customize features on a per-website basis. If you have several content types exported as separate features, but a website needs a subset of those content types, you can disable the unused features for a cleaner content editing experience. This also has the advantage of logically grouping features and custom code alongside its corresponding configuration.

The downside to the more granular approach is Features can’t make some of the same assumptions as the core configuration system. Features relies much more heavily on the developer to manage the architecture and handle configuration changes Features can’t handle. Relying on the developer to handle configuration changes makes the system much more error-prone and more of a burden to maintain.

To configure a Features-based workflow, you must configure cm.strategy to features in the blt/blt.yml file.

Using bundles

Features allows you to define custom “bundles” essentially letting you train Features to support your project’s individual workflow. Bundles are a way to namespace your features. You want to choose a bundle name based on your project name (an Acme bundle would prefix all your feature server names with acme\_).

Bundles can also do more to make your life easier. For instance, Features automates suggested features based around content types and taxonomies. If you want to create features for custom block types, for example, you can configure your preference in the custom bundle. You can choose to exclude certain types of configuration. You can exclude permissions, or group certain types of configuration such as field storage into a core bundle, which is helpful for breaking circular dependencies.


As of version 8.3.3, Features can manage user roles and permissions, but not independently. You can only export permissions for an entire role at once, unlike in Drupal 7, where you can export roles and their associated permissions separately.

For this reason, Features excludes roles and permissions by default. If you want to export roles and permissions, change the alters configuration on your Features bundle, see User permission handling.

Testing features

You must ensure, through automated testing, your features can be installed on a new website and enabled on existing sites.

Features can fail to install or import properly for various reasons. The most frequent cause is circular dependencies. For instance, if feature A depends on a field exported in feature B, and feature B depends on a field exported in feature A. You can’t enable either feature first, and website installs will break. Circular dependencies are not important if you have a single-website installation, but you want to prevent them if you are building a multisite platform.

A feature can also stay overridden after importing, due to another module overriding the provided configuration. For instance, the Workbench module adds a special field to content types when enabled. If the field is not exported to the feature containing a content type, the feature will be perpetually overridden. Overriding the features is not necessarily harmful, but can make it difficult to diagnose other more serious issues. Acquia recommends configuring Acquia BLT’s CM allow overrides property to false to automate testing for overrides.

You can use the following code snippet in your profile’s install file to enable all features in a given bundle:

$available_modules = system_rebuild_module_data();
$dependencies = array();
foreach ($available_modules as $name => $module) {
  if ($module->info['package'] == 'My Bundle') {
    $dependencies[] = $name;

Updating custom fields and schema

Features and the core configuration system don’t handle some configuration changes well, including:

  • Updating field storage such as changing a single-value field to an unlimited-value field
  • Adding a new custom block type to an existing feature. You must create a new feature for every block type
  • Deleting a field (you must remove the field from the feature and then use the following code snippet to delete the field)
  • Adding a field to some types of content (such as block content)
  • Adding several configuration entities at once depending on one another (leading to cryptic exceptions when you run features-import, use the following workaround)

To handle the configuration changes, you want to use update hooks. For example, you can use the following snippet of code to create or delete a field:

use Drupal\field\Entity\FieldStorageConfig;
use Drupal\field\Entity\FieldConfig;

// Create a new field.
module_load_include('profile', 'foo', 'foo'); // See below; foo is your profile name.
$storage_values = foo_read_config('', 'foo_feature');
$field_values = foo_read_config('field.field.block_content.foo_my_block.field_my_new_field', 'foo_feature');

// Delete an existing field.
$field = FieldStorageConfig::loadByName('block_content', 'field_my_field');

The preceding code depends on a helper feature such as the following code, which Acquia suggests adding to your custom profile. Lightning includes the helper feature out-of-the-box:

use Drupal\Core\Config\FileStorage;
use Drupal\Core\Config\InstallStorage;

 * Reads a stored config file from a module's config/install directory.
 * @param string $id
 *   The config ID.
 * @param string $module
 *   (optional) The module to search. Defaults to 'foo' profile (not technically
 *   a module, but profiles are treated like modules by the install system).
 * @return array
 *   The config data.
function foo_read_config($id, $module = 'foo') {
  // Statically cache all FileStorage objects, keyed by module.
  static $storage = [];

  if (empty($storage[$module])) {
    $dir = \Drupal::service('module_handler')->getModule($module)->getPath();
    $storage[$module] = new FileStorage($dir . '/' . InstallStorage::CONFIG_INSTALL_DIRECTORY);
  return $storage[$module]->read($id);

Overriding configuration

Drupal typically prevents modules from overriding configuration that already exists in the system, producing an exception such as the following:

Configuration objects (foo) provided by bar already exist in active configuration

If you must override the default configuration provided by another project (or core), the available solutions include:

  • Recommended: use Features. Features will prevent a PreExistingConfigException from being thrown when a feature containing pre-existing configuration is installed. Ensure Features is already enabled before installing any individual features containing configuration overrides (listing Features as a dependency is not enough).
  • Move your configuration into a custom profile. Configuration imports for profiles are treated differently than for modules. Importing pre-existing configuration for a profile won’t throw a PreExistingConfigException.
  • Use config rewrite, which will allow you to rewrite the configuration of another module prior to installation.
  • Use the config override system built into core. For awareness, the configuration override system has some limitations.

Other caveats

Be aware that reverting all features and configurations on every deploy creates a risk of discarding server-side changes. You must control the risk by managing permissions with caution. You must balance the risk against the greater risk of allowing for divergent configuration between your database and VCS.

Configuration Management in Drupal 8 is still improving early in the Drupal 8 lifecycle. You must continue to watch Drupal Core’s issue queue and Drupal Planet blog posts for refinements to the CM workflows explained here.

Features is a ground-up rewrite in Drupal 8 and is maturing fast, but may still have some traps. Developers must keep a close eye on exported features, and architects must review features in pull requests for the preceding caveats and best practices.