This overview outlines the steps to prepare an existing Drupal site for upgrade or migration to Drual 9 with Integrated Composer.
Upgrade to the latest Drupal 8.9 release.
- Although Drupal supports upgrading to Drupal 9 from Drupal 8.8, ensure that your site is on the latest Drupal 8.9 release before trying Drupal 9 on Pantheon.
Review the How to Prepare Your Drupal 7 or Drupal 8 Site for Drupal 9 guide on Drupal.org.
Use the Upgrade Status Drupal 8/9 module to generate a full report of your site’s compatibility.
Help contributed modules prepare for Drupal 9, for example by updating modules' deprecated API usages and converting tests to PHPUnit.
Check out Acquia’s Drupal 9 Deprecation Status Upgrade Tracker for information about Drupal 9 support for contributed Drupal modules and themes.
Drupal 9 has deprecated a number of different functions and APIs in favor of better options going forward.
node_load() was replaced in Drupal 9 with
Node::load resulting in this change needed:
$node = node_load(1);
use \Drupal\node\Entity\Node; $node = Node::load(1);
Since most of these changes are relatively minor, there are a number of deprecation checking and correction tools available.