[openstack-dev] [Fuel] Compatibility of fuel plugins and fuel versions

Patrick Petit ppetit at mirantis.com
Fri Mar 11 15:08:25 UTC 2016

On 11 March 2016 at 15:45:57, Simon Pasquier (spasquier at mirantis.com) wrote:
Thanks for kicking off the discussion!

On Thu, Mar 10, 2016 at 8:30 AM, Mike Scherbakov <mscherbakov at mirantis.com> wrote:
Hi folks,
in order to make a decision whether we need to support example plugins, and if actually need them [1], I'd suggest to discuss more common things about plugins.

My thoughts:
1) This is not good, that our plugins created for Fuel 8 won't even install on Fuel 9. By default, we should assume that plugin will work at newer version of Fuel. However, for proper user experience, I suggest to create meta-field "validated_against", where plugin dev would provide versions of Fuel this plugin has been tested with. Let's say, it was tested against 7.0, 8.0. If user installs plugin in Fuel 9, I'd suggest to show a warning saying about risks and the fact that the plugin has not been tested against 9. We should not restrict intsallation against 9, though.

From a plugin developer's standpoint, this point doesn't worry me too much. It's fairly easy to hack the metadata.yaml file for supporting a newer release of Fuel and I suspect that some users already do this.
And I think that it is good that plugin developers explicitly advertise which Fuel versions the plugin supports.
That being said, I get the need to have something more automatic for CI and QA purposes. What about having some kind of flag/option (in the Nailgun API?) that would allow the installation of a plugin even if it is marked as not compatible with the current release?


2) We need to keep backward compatibility of pluggable interface for a few releases. So that plugin developer can use pluggable interface of version x, which was supported in Fuel 6.1. If we still support it, it would mean (see next point) compatibility of this plugin with 6.1, 7.0, 8.0, 9.0. If we want to deprecate pluggable interface version, we should announce it, and basically follow standard process of deprecation.

+1 and more.
From my past experience, this is a major issue that complicates the plugin maintenance. I understand that it is sometimes necessary to make breaking changes but at least it should be advertised in advance and to a wide audience. Not all plugin developers monitor the Fuel reviews to track these changes...

3) Plugin's ability to work against multiple releases of Fuel (multi-release support). If if..else clauses to support multiple releases are fairly minimal, let's say take less that 10% of LOC, I'd suggest to have this supported. Just because it will be easier for plugin devs to support their plugin code (no code duplication, single repo for multiple releases).

From my experience (and assuming that framework compatibility isn't broken), this is usually what happens. You need a few if clauses to deal with the differences between releases N and N+1 but this is manageable.

Probably one of the most single important thing to have to be able to upgrade a deployed environment with a new plugin version!



[1] http://lists.openstack.org/pipermail/openstack-dev/2016-March/088211.html
Mike Scherbakov

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