[openstack-dev] [Nova] Support for Pecan in Nova

Ryan Petrello ryan.petrello at dreamhost.com
Wed Dec 11 20:41:38 UTC 2013


I’ve spent the past week experimenting with using Pecan for Nova’s API, and have opened an experimental review:


…which implements the `versions` v3 endpoint using pecan (and paves the way for other extensions to use pecan).  This is a *potential* approach I've considered for gradually moving the V3 API, but I’m open to other suggestions (and feedback on this approach).  I’ve also got a few open questions/general observations:

1.  It looks like the Nova v3 API is composed *entirely* of extensions (including “core” API calls), and that extensions and their routes are discoverable and extensible via installed software that registers itself via stevedore.  This seems to lead to an API that’s composed of installed software, which in my opinion, makes it fairly hard to map out the API (as opposed to how routes are manually defined in other WSGI frameworks).  I assume at this time, this design decision has already been solidified for v3?

2.  The approach in my review would allow us to translate extensions to pecan piecemeal.  To me, this seems like a more desirable and manageable approach than moving everything to pecan at once, given the scale of Nova’s API.  Do others agree/disagree?  Until all v3 extensions are translated, this means the v3 API is composed of two separate WSGI apps.

3.  Can somebody explain the purpose of the wsgi.deserializer decorator?  It’s something I’ve not accounted for yet in my pecan implementation.  Is the goal to deserialize the request *body* from e.g., XML into a usable data structure?  Is there an equivalent for JSON handling?  How does this relate to the schema validation that’s being done in v3?

Ryan Petrello
Senior Developer, DreamHost
ryan.petrello at dreamhost.com

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