- May 2012 - One year have past since I initially wrote this article. Upgrading these days from Drupal 6 to 7 have become easier, safer, and a lot less nerve wrecking, though it will never become a cakewalk.
- May 2015 - Started writing a longer series using Migrate and Migrate D2D.
- May 2015 - Cleaned up language a corrected grammar erros.
## To migrate or upgrade?
As writing do I still have a few more complex sites running on Drupal 6. Knowing these sites, their complexity, and all existing glue code, a fast and easy upgrade will be hard pull off. It might be easier for complex sites to only migrate the content using modules like migrate and migrate_d2d.
### A data migration
- Do a clean Drupal 7 installation.
- Build basic needed content types and configurations.
- Recreate the theme in D7 or port you existing CSS/SASS styles.
Then migrate your content by using modules like http://drupal.org/project/feeds, or for even more flexibility and power http://drupal.org/project/migrate. I'll promise do a blog post of a more complex Drupal 6 to 7 migration as soon as my remaining sites are running Drupal 7.
The upgrade process. What core upgrades what not
First thing first. It is vital to understand this. Drupal core it self upgrade just perfectly from 6 to 7. Meaning if you are running a super small and simple installation of Drupal 6, the upgrade it self should be a breeze. Before you attempt to upgrade read the short but concise UPGRADE.txt located in your Drupal root directory, and make sure you understand it before attempting to run any upgrade.
## 3 part modules
The tricky part of the upgrade is getting all the extra modules you have installed upgraded. The fewer modules your site is using, the simpler your upgrade path will be. So before you even begin. Make sure your site uses only uses modules it REALLY need. Make sure you properly uninstall the modules you decide to get rid of. Uninstalling help Drupal to keep the database clean and with as little as possible orphan data and configurations.
## Modules dies, morph and some even get eaten by core
Drupal 7 is now into its third year of development. All this time have given the core developers a lot of time to add some pretty impressive new features, but also time to do a lot of changes to modules and exiting functionality.
Daniel wrote this post a while back http://www.unleashedmind.com/en/blog/sun/more-than-50-drupal-modules-mo… that is relly worth its read. It is pretty vital to understand how this will affect your upgrade path and planning. The rule of thumb is. Modules that get included into core are still responsible for providing an upgrade path of the configuration and data. This will not be provided by core is self.
A good example is http://drupal.org/project/cck. that got moved or even more correctly, replaced by core in Drupal 7. Core it self does not migrate any of the fields provided by CCK during the Drupal 6 to 7 upgrade. This upgrade have to be performed by CCK it self meaning you will need the Drupal 7 version of CCK to upgrade to Drupal 7 field system. It comes with its own UI that enable you to select and see what field that you have, have not upgraded. It also work as a API allowing other CCK-based fields to provide its own upgrade path.
## Plan you upgrade and stay away from the blues
Larger sites is naturally more complicated to upgrade and will require quite some planning. Read up on the different module project pages documentation, look for issues and try to come up with battle plan per module.
I find that we are in better shape then we where back in the days when we moved from Drupal 5 to 6, but there still projects dragging their feet's and have not yet provided a Drupal 7.x branch or/and a upgrade path. Search the project issue queue for Drupal 7 port related titles and join the conversation. Even better, help testing out patches or provide the maintainer(s) with your own beautiful hand crafted code.
## Architecture change
Changes in D7 architecture will force some modules to die or to morph into other projects. Here is a few examples where a lot of stuff is changing:
- Reference stuff, http://drupal.org/project/references
- Views attachment, http://drupal.org/project/eva
- GEO-stuff, http://drupal.org/project/addressfield, http://drupal.org/project/geofield
- Media-suff, http://drupal.org/project/media