Drupal 8 Configuration - Part 2: How the API works

This is part two of a five-part series of articles exploring the Drupal 8 Configuration API, how it enables functionality to be migrated between multiple environments, and ways of using the Configuration API with contributed modules to effectively manage the configuration of a project.

13 May 2019

Background

We live in an age of Drupal complexity. In the early days of Drupal, many developers would have a single Drupal instance/environment (aka copy) that was their production site, where they would test out new modules and develop new functionality. Developing on the live website however sometimes met with disastrous consequences when things went wrong! Over time, technology on the web grew, and nowadays it's fairly standard to have a Drupal project running on multiple environments to allow site development to be run in parallel to a live website without causing disruptions. New functionality is developed first in isolated private copies of the website, put into a testing environment where it is approved by clients, and eventually merged into the live production site.

While multiple environments allow for site development without causing disruptions on the live production website, it introduces a new problem; how to ensure consistency between site copies so that they are all working with the correct code.

This series of articles will explore the Configuration API, how it enables functionality to be migrated between multiple environments (sites), and ways of using the Configuration API with contributed modules to effectively manage the configuration of a project. This series will consist of the following posts:

Part 1 gives the background of the Configuration API, as well as discusses some terminology used within this article, so it's worth a read before beginning this article.

Active configuration is in the database

In Drupal 8, configuration used at runtime is stored in the database. The values in the database are known as active configuration. In Drupal 7, configuration was known as settings, and stored in the {variable} table. In Drupal 8, configuration is stored in the {config} table. The active configuration is used at runtime by Drupal when preparing responses.

Configuration is backed up to files

The Configuration API enables the ability to export the active database configuration into a series of YML files. These files can also be imported into the database. This means that a developer can create a new Field API field on their local development environment, export the configuration for the new field to files, push those files to to the production environment, then import the configuration into the production environment's active configuration in the database.

The configuration values in the database are the live/active values, used by Drupal when responding to requests. The YMLfiles that represent configuration are not required, and are not used at run-time. In fact, in a new system the configuration files don't even exist until/unless someone exports the active configuration from the database. The configuration files are a means to be able to back up and/or migrate configuration between environments. Configuration files are never used in runtime on a site.

Configuration architecture

Let's look at the Configuration API on a more technical level, using a real-world example. The Restrict IP module allows users to set a list of rules that whitelist or blacklist users based on their IP address. Upon visiting the module settings page, users are presented with a checkbox that allows them to enable/disable the module functionality.

From a data standpoint, checkboxes are booleans; they represent either a true or false value. When exporting the configuration of a site with the Restrict IP module enabled, the relevant configuration key will be saved with a value of either true or false to a .yml file. Modules are required to define the schema for any configuration the module creates. Developers can look at the configuration schema declarations to understand what file(s) will be created, and what values are accepted.

Modules declare the schema for their configuration in the [MODULE ROOT]/config/schema directory. In the case of the Restrict IP module, the schema file is restrict_ip/config/schema/restrict_ip.schema.yml. This file contains the following declaration:

restrict_ip.settings:
  type: config_object
  label: 'Restrict IP settings'
  mapping:
    enable:
      type: boolean
      label: 'Enable module'

Schema declarations tell the system what the configuration looks like. In this case, the base configuration object is restrict_ip.settings, from the first line. When this configuration is exported to file, the file name will be restrict_ip.settings.yml. In that file will be a declaration of either:

enable: true

Or:

enable: false

When the file restrict_ip.settings.yml is imported into the active configuration in another environment's database, the value for the enable key will be imported as defined in the file.

On top of this, enabled modules are listed in core.extension.yml, which is the configuration that tracks which modules are enabled in a given environment. When the Restrict IP module is enabled in one environment, and configuration files exported from that environment are imported into a different Drupal environment, the Restrict IP module will be enabled due to its existence in core.extension.yml, and the setting enable will have a value of either true or false, depending on what the value was exported from the original environment.

Note that if you were to try to import the configuration without having the Restrict IP module in the codebase, an error will be thrown and the configuration import will fail with an error about the Restrict IP module not existing.

Summary

In this article, we looked at how the Drupal 8 Configuration API works on a technical level. We looked at how active configuration lives in the database, and can be exported to files which can then be imported back into the database, or migrated and imported to other Drupal environments. In part 3 of the series, Using the API, we will look at how to actually use the Configuration API, as well as some contributed modules that extend the functionality of the Configuration API, allowing for more effective management of Drupal 8 projects.