How Can You Estimate the Complexity of a Drupal 7 to Drupal 9 Migration?

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The greatest and latest release of Drupal - Drupal 9 has been released in June 2020. Since the release of Drupal 8, the release model of Drupal is designed to support innovation. Every 6 months there will be a new release with a set of bug fixes and feature additions.

complexity of D7 to D9

If you are still in Drupal 7, it is time to think about migrating to Drupal 9 as Drupal 7 will reach end of life in November 2022. Drupal 8 will reach the end of life before that, but if you are in Drupal 8, you do not have to worry much, Drupal 8 to 9 upgradation is easier as you do a minor update in Drupal. But in the case of Drupal 7 or Drupal 6 to Drupal 9, things are much more complex.


Since Drupal 7 and Drupal 9 are based on two different code bases, to migrate from one to another, a new Drupal 9 instance needs to be setup with the required modules enabled and then execute the migration process to pull content and configuration from the Drupal 7 database.  If you do not plan it well, there is a high risk involved.

The first step in the planning process is to assess the complexity of the existing website and come up with a migration strategy that is suitable for your website.

Since this is a new build in Drupal 9 and migrating the content from your Drupal 7, the following information from your existing Drupal 7 website will help you estimate the complexity of the website as well as the effort required for migration.

  • List of contributed modules with their D9 readiness

  • List of custom modules with lines of code and key hooks used

  • List of content types with number of content as well as fields

  • List of views

  • List of features

  • List of vocabularies and number of terms

  • List of themes with the templates used

  • List of CSS/JS files used

  • Number of lines of code in template.php file

To help you quickly get this information, we have created a Drush command that helps you prepare a report from your Drupal 7 site with all the required information for an estimation.