tl;dr: Have a look at https://review.openstack.org/#/c/329386/ to help move some placement API decisions along.
Not really that long, do read: As part of the generic resource pools spec[1] a new, independent of the rest of nova, API is being developed called the "Placement API". The API will initially allow for the management of resource providers. There are entities which provide classes of resources[2] such as VPCU, DISK_GB, IPV4_ADDRESS. At the Bristol mid-cycle it was decided that the placement api should be developed in such a way that it will be easy™ to lift it into its own project at some date in the future. In that future the placement api will be able to help "place" lots of things, not just instances. It was also decided that this lift and shift afforded an opportunity to explore ways of hosting and testing an HTTP API that are different from the modes originated in nova. Not for the sake of being different but because the nova way has issues including inscrutability. I started a WIP a few months back to start exploring this new API. Recently it's been chunkified into smaller reviews[3]. For testing I've been using gabbi[4] because it does good TDD for this kind of thing and also does a great job of satisfying the declarative proposal in the api-wg testing guideline[5]. I hope this is not controversial. Where the controversy enters the picture has been in my choice of how to structure the code that hosts the API. It's been clear from the start that we want to use as little of the nova infrastructure as possible. What's undecided is which of two strategies should be followed. In broad strokes those strategies are: * Go all in on a common framework, probably Flask[6], and use it in its own specific way. * Don't use a framework at all. WSGI has never needed one. Just compose some WSGI-apps, middleware and utilities and let them do their work. For now I've chosen the latter because it provides a level of simplicity, inspectability, testability and control that I think is lost when using a framework. I know for many people in the OpenStack community not using a framework goes against the grain, but have a look at the code[7], it's pretty simple Python. One of the dependencies in this model is selector[8]. The discussion around the review of getting it into global-requirements[9] is what has prompted this email. Discussion there has suggested that the resistance to the second strategy may be significant enough that we should go with the first one. I think we need to decide that sooner than later so this email is an invitation to join in the discussion, either here or on the review of selector[9] or the initial API[3].
From my standpoint, as the person writing the initial code, it would be
great to get this resolved soon. If we need to make a change, making a simple WSGI app into a working Flask app is something other than trivial, but I value us having consensus over how to do this over my feelings about Flask and frameworks. To be clear: I don't like Flask, at all, it is too magic and too obscuring of the way HTTP works. You have to commit to it all the way to get the most benefit from it and when you do that a lot of inspectability is lost behind implicit magic and you are stuck with it henceforth. Implicit magic is absolutely horrible for long term maintenance, especially in communities where many of the contributors come and go. The code I've written in the WIP tries to break with many of code trends that require readers to guess. [1] http://specs.openstack.org/openstack/nova-specs/specs/newton/approved/generic-resource-pools.html [2] http://specs.openstack.org/openstack/nova-specs/specs/mitaka/implemented/resource-classes.html[3] https://review.openstack.org/#/c/329149/ and its descendants [4] https://gabbi.readthedocs.io/
[5] http://specs.openstack.org/openstack/api-wg/guidelines/testing.html#proposals [6] http://flask.pocoo.org/ [7] https://review.openstack.org/#/c/329151/10/nova/api/openstack/placement/handlers/resource_provider.py [8] https://pypi.python.org/pypi/selector [9] https://review.openstack.org/#/c/329386/ -- Chris Dent (╯°□°)╯︵┻━┻ http://anticdent.org/ freenode: cdent tw: @anticdent
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