Preparing Your Drupal 8 Site for Drupal 9

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From a project planning perspective, what do organizations need to consider when planning for the Drupal 9 upgrade? What technical details should developers pay attention to? We’ve discussed who should upgrade to Drupal 9 and when to upgrade to Drupal 9. Here’s how to do it.

Drupal 9 Upgrade Project Planning

Plan a release window

Drupal 9 has been released. Drupal 8.9.x is scheduled to reach end-of-life in November 2021, with older versions, such as 8.7.x, slated to stop receiving security support in June 2020. You first need to plan a release window to upgrade to Drupal 8.9.x during this timeframe to make sure your site is upgraded before the older Drupal versions are no longer supported.

Once on Drupal 8.9, you can perform and release all the preparatory work described below. After that, you’ll be ready to plan a release window for the final upgrade to Drupal 9. 

For more on planning a release window, check out Drupal 8 Release Planning in the Enterprise. Remember to factor in other development work, updates for the rest of your stack, and other ongoing development projects, and give yourself plenty of time to complete the work.

Scope the upgrade project

To scope the upgrade project, you'll need to consider a handful of factors:

  • Deprecated code that must be updated
  • Other development work that you'll do as part of the upgrade project

We'll dive deeper into how to check for and correct deprecated code and APIs shortly, but first, let's take a look at other development work you might do as part of the upgrade project.

Solicit feature requests from stakeholders

Does your website deliver stakeholder-required features using contributed modules that haven't yet been updated for Drupal 9? Do your key stakeholders want new features to serve site users better or meet business objectives? 

For many organizations, major Drupal re-platforming efforts have provided a cadence for other website development work, including new feature development. If it's been a while since your organization checked in with stakeholders, now might be a good time to do that. 

Regardless of whether or not you plan to deliver new feature development in the Drupal 9 upgrade project, it's a good idea to make sure you won't lose Drupal 8 contributed modules that provide the functionality your stakeholders can't live without - unless you've got a new way to deliver that functionality in Drupal 9.

Architecture, content, accessibility audits, and more

For sites that are already on Drupal 8, the Drupal 9 upgrade is different than many previous major version updates; Drupal 8 to Drupal 9 does not require a content migration, so there's no real need to do a major information architecture audit and overhaul. In this new world, organizations should look at shifting the site redesign and content architecture cadence to an ongoing, iterative model.

How to Prepare for Drupal 9

Upgrade to Drupal 8.8 or Drupal 8.9

If you haven't already updated your Drupal 8 site to the most recent version of Drupal 8.x, that's where you must start. Drupal 8.8 was a big milestone for API compatibility; it's the first release with an API that's fully compatible with Drupal 9. Practically speaking, this means that contributed modules released prior to 8.8 may not be compatible with Drupal 9.

Beyond API compatibility, Drupal 8.8 and 8.9 introduce further bugfixes, as well as database optimizations, to prepare for Drupal 9. If you upgrade your website and all contributed modules and themes to versions that are compatible with 8.9, those parts of your site should be ready for Drupal 9. 

Platform requirements 

One change between Drupal 8 and Drupal 9 is that Drupal 9 requires a minimum of PHP 7.3. Drupal 8 recommends but does not require 7.3. There are new minimum requirements for MYSQL and MariaDB and other databases. And your Drush version, if you use Drush, must be Drush 10. If you need to update any of these, you should be able to do it while still on Drupal 8, if you like. There may be other changes to the Drupal 9 requirements in the future, so double-check the environment requirements.

Audit for conflicting dependencies

Composer manages third-party dependency updates and will update Drupal dependencies when you do Composer updates. However, if anything else in your stack, such as contributed modules or custom code, has conflicting dependencies, you could run into issues after you update. For this reason, you should check your code for any third-party dependency that conflicts with the core dependencies. 

For example, Drupal 9 core requires Symfony 4.4, while Drupal 8 worked with Symfony 3.4. If you have contributed modules or custom code that depends on Symfony 3.4, you'll need to resolve those conflicts before you update to Drupal 9. If your code works with either version, you can update your composer.json to indicate that either version works. For instance, the following code in your module’s composer.json indicates that your code will work with either the 3.4 or 4.4 version of Symfony Console. This makes it compatible with both Drupal 8 and Drupal 9 and any other libraries that require either of these Symfony versions.

{
  "require": {
    "symfony/console": "~3.4.0 || ^4.4"
  }
}

If you have code or contributed modules that require incompatible versions of third party libraries and won’t work with the ones used in Drupal 9, you’ll have to find some way to remove those dependencies. That may mean rewriting custom code, helping your contributed modules rewrite their code, or finding alternative solutions that don’t have these problems.

Check for deprecated code

Sites that are already on Drupal 8 can see deprecated code using a few different tools:

  • IDEs or code editors that understand `@deprecated` annotations;
  • Running Drupal Check,  PhpStan Drupal, or Drupal Quality Checker from the command line or as part of a continuous integration system to check for deprecations and bugs;
  • Installing the Drupal 8 branch of the Upgrade Status module to get Drupal Check functionality, plus additional scanning;
  • Configuring your test suite to fail when it tries to execute a method that calls a deprecated code path.

See Hawkeye Tenderwolf’s article How to Enforce Drupal Coding Standards via Git for more ideas. That article explains how Lullabot uses GrumPHP and Drupal Quality Checker to monitor code on some of our client and internal sites.  

Many organizations already have solutions to check for deprecated code built into their workflow. Some organizations do this as part of testing, while others do it as part of a CI workflow. In the modern software development world, these tools are key components of developing and maintaining complex codebases.

While you can do this check in any version of Drupal 8, you’ll need to do a final pass once you upgrade any older Drupal 8 version to Drupal 8.8, because new deprecations have been identified in every release up to Drupal 8.8.

Refactor, update and remove deprecated code

If you find that your site contains deprecated code, there are a few avenues to fix it prior to upgrading to Drupal 9. Some of those tools include:

Flag modules as Drupal 9 compatible

Once you’ve removed deprecated code from your custom modules, flag them as being compatible with both Drupal 8 and Drupal 9, by adding the following line to your module’s info.yml file.

core_version_requirement: ^8 || ^9

What about contributed modules?

If you're using contributed modules that are deprecated, work with module maintainers to offer help when possible to ensure that updates will happen. You can find Drupal 9 compatible modules, check reports in the drupal.org issue queue for Drupal 9 compatibility, or by checking Drupal 9 Deprecation Status.

You should update all contributed modules to a Drupal 9-compatible version while your site is still on Drupal 8. Do this before attempting an upgrade to Drupal 9!

Update to Drupal 9

One interesting aspect of the Drupal 9 upgrade is that you should be able to do all the preparatory work while you’re still on Drupal 8.8+. Find and remove deprecated code, update all your contributed modules to D9-compatible versions, etc. Once that is done, updating to Drupal 9 is simple:

  1. Update the core codebase to Drupal 9.
  2. Run update.php.

Drupal 9.x+

The Drupal Association has announced its intent to provide minor release updates every six months. Assuming Drupal 9.0 releases successfully in June 2020, the Drupal 9.1 update is planned for December 2020, with 9.2 to follow in June 2021.

To make Drupal 9.0 as stable as possible, no new features are planned for Drupal 9.0. The minor updates every six months may introduce new features and code deprecations, similar to the Drupal 8 release cycle. With this planned release cycle, there is no benefit to waiting for Drupal 9.x releases to upgrade to Drupal 9; Drupal 9.0 should be as stable and mature as Drupal 8.9.

Other resources

Karen Stevenson

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Karen is one of Drupal's great pioneers, co-creating the Content Construction Kit (CCK) which has become Field UI, part of Drupal core.