PHP announced last year that the version 5.4 is going to be unsupported. That represents a problem for Drupal 6 users, because Drupal 6 may produce errors or unexpected behavior with a PHP version higher than 5.4.
Given that announcement, it’s expected that soon, hosting companies will discontinue support of PHP 5.4, which means that Drupal 6 users will need to customize their Drupal site to support that new version of PHP, or upgrade to a higher version of Drupal.
Migrating from Drupal 6 to Drupal 7 or 8 is not straight forward, and creating a migration plan is highly recommended. These are common examples of things that can go wrong:
- Drupal Node IDs and URLs are not considered in the migration plan and therefore they change in the new website. This will lead to a lot of 404 issues, and SEO will be impacted as well.
- Content and taxonomies are migrated but their relationships are lost.
- Custom modules that use deprecated functions are not compatible with the new Drupal version. You will end developing new code for your site.
- Contrib Drupal modules (3rd party modules developed by the Drupal community) are discontinued in the new Drupal version. In this case you may consider losing functionality in the new site or replacing those modules with other modules that do the same.
- The existing Drupal template is not compatible with the new version of Drupal. You may end redesigning your site based upon an existing template supported by the Drupal version you are migrating to.
In any case, you should evaluate the effort that will take migrating the exact same website to the new version of Drupal, and decide if it’s easier to refactor the existing site in Drupal 7, Drupal 8 or even in a different CMS like WordPress, and just migrate content and users.
We recently helped the Climate Change Resource Center migrating their website from Drupal 6 to Drupal 7.
These are two projects that could help you performing that migration:
- https://www.drupal.org/project/migrate
- https://www.drupal.org/project/migrate_d2d
