Testing against the latest milestone release of Confluence 2.8, it's clear that swathes of plugins are going to need to be re-released to handle the changes..
As with any plugin architecture, plugins are dependant upon the API of the parent application. With each point release (2.3, 2.4, 2.5, etc) of Confluence, the API changes, but usually only a little.
Confluence 2.8, however, is one of those releases where the changes are pretty big and widespread, especially for the larger plugins. Many classes no longer exist and have been replaced by completely new classes so plugin developers will have their work cut out for them.
That being said, Confluence 2.8 is a great step forward and the milestone releases are proving invaluable to detect the compatibility issues sooner rather than later.
It's not yet known when 2.8 will be formally released, but due to the nature of some of the changes I dare say it's going to be a few months before the more complex plugins catch up. In short, if you use lots of plugins (especially those that are cluster-aware), don't go upgrading your production environment to 2.8 the day it's released!
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Dan has spoken with Don Brown and apparently this is a known issue and should be cleared up before release
More specifically they're working on it. They try not to break things, but sometimes it's required. Even if Confluence 2.8 breaks APIs hard, then the last time that happened in any seriousness was v2.3 well over a year ago.
Once 2.8 is closer to final we should see things ironed out, but in order for there to be even a chance for that to happen we must feed the breakages back to them.
That's exactly why these milestone releases are so useful to ourselves and our customers. Hopefully as Atlassian get more feedback from the milestone releases they'll be able to benefit from them as much as we do
For any plugin authors out there reading this - do test against the Milestone releases and let Atlassian know of any problems you encounter.
Maybe things have changed, but back when I used to be responsible for maintaining a Confluence environment (around the 2.2 time) we would always wait for at least the x.x.1 release before upgrading since x.x.0 normally had issues
Do you know whats specifically broken for plugins on clustered environments? All I can see in the latest release notes is that they have "Upgrade issue for clustered deployments. Don't use this Milestone on a Cluster."
Builder uses cluster-safe caches for the flattened layout & css/js data, and it is these that are breaking on 2.8-m6, specifically spring is throwing a class conversion exception when setting the cacheManager.
Aah, so thats that same issue as CONF-10602 I'm guessing