A lot of people are asking themselves if they should upgrade from joomla 1.0 to joomla 1.5. There's quit some information which can be found on this topic on the official joomla site and forum, but I thought it might be a good idea to gather that information, put it in one article and give my own view on some topics.

Simple upgrade is not possible.

Joomla 1.5 is very different from joomla 1.0. In fact a big part of the code and the API was completely rewritten. This is the reason why it was decided not to provide an upgrade path. Upgrade means that you can overwrite your existing installation, maybe execute some SQL queries and your site is upgraded. It was nearly impossible to provide such a feature for joomla 1.5, so in stead a migrate path was provided. The difference is that for a migration path, you'll have to do a fresh install of joomla 1.5 (including all extensions you are using) and afterwards you'll have to migrate your data. There exists a migration tool to help you with this, but this will only work for data of the core modules, not of third party modules.

Do I need to upgrade?

Before you start with the migration, ask yourself if you really need to migrate to joomla 1.5. Although joomla 1.5 has a lot of new cool features, I would advice not to migrate unless you really need to. Migrating an existing site with a lot of data and a lot of third party modules, might be quit a task. For some 3rd party extensions, it might be very difficult to migrate the data. Note also that at the time of writing this article, there is no stable release of joomla 1.5 yet. This means that all joomla1.5-RC2 sites will have to upgrade to the first stable release in the (near?) future. As I experienced myself when upgrading from RC1 to RC2, this might give problems. Again, the problems you might have will be with 3rd party extensions. My advice would be to wait with your migration until the first stable release of joomla 1.5.

Can I start now?

Before you start, you'll have to check if it's even possible for you to migrate. A lot of extensions are not yet joomla 1.5 compatible. So don't start migrating, before you verified if all your extensions are 1.5 compatible. Note that some extensions claim to be 1.5 compatible, but are in fact not. In the ideal world, every extension should work once you enabled the legacy plugin. My experience however is that this is not the case for a lot of extensions. Take into account that it can happen that you migrate and at the end, one of your essential third party extensions isn't working properly. So don't throw away your joomla 1.0 site before your new joomla 1.5 has been tested!

Let's do it

You'll have to perform an automated migration for your core data and a manual migration for your third party data. This is very clearly explained on the official migration tool manual. Some remarks on this page though:

• The link to the migration component is broken as it was moved recently. The migrator component can be found here now.
• Quit some people have had problems with this migration tool. With the latest version of the tool however, it should work for most installations.
• People who are having problems anyhow can report this in the migration tool topic on the joomla forum.
• There will be a complete Migration Guide. At the time of writing this article, it's not ready yet.

Some conclusions and advices

• Migration is perfectly possible and as long as you follow the migration instructions, you'll probably won't have to many problems. Keep however always in mind that it might turn out to be a difficult task and that you might have to switch back to joomla 1.0.
• If you have a lot of third party extensions with data that needs to be migrated, migration could give quit some problems. Certainly if you're not really a techie and run into migration problems, it can turn out to be a real nightmare.
• Don't do migration unless you really need or want to. If you're for example a hosting provider and joomla is one of the services you provide, then I don't think you'll want to explain to dozens of (mostly non technical) clients how they should upgrade.
• If you are starting a brand new site and you have to choose between joomla 1.0 and joomla 1.5, then spare yourself a future migration and go for joomla 1.5 if possible.
• This article is not meant to criticize the joomla developers. I can perfectly understand their decision not to provide an upgrade path.

Frederik.