[openstack-dev] [nova][api] Microversions. And why do we need API extensions for new API functionality?

Attila Fazekas afazekas at redhat.com
Mon Mar 9 08:58:10 UTC 2015

I agree with Jay.

The extension layer is also expensive in CPU usage,
and it also makes more difficult to troubleshoot issues.

----- Original Message -----
> From: "Jay Pipes" <jaypipes at gmail.com>
> To: "OpenStack Development Mailing List" <openstack-dev at lists.openstack.org>, "Sergey Nikitin"
> <snikitin at mirantis.com>
> Sent: Sunday, March 8, 2015 1:31:34 AM
> Subject: [openstack-dev] [nova][api] Microversions. And why do we need API extensions for new API functionality?
> Hi Stackers,
> Now that microversions have been introduced to the Nova API (meaning we
> can now have novaclient request, say, version 2.3 of the Nova API using
> the special X-OpenStack-Nova-API-Version HTTP header), is there any good
> reason to require API extensions at all for *new* functionality.
> Sergey Nikitin is currently in the process of code review for the final
> patch that adds server instance tagging to the Nova API:
> https://review.openstack.org/#/c/128940
> Unfortunately, for some reason I really don't understand, Sergey is
> being required to create an API extension called "os-server-tags" in
> order to add the server tag functionality to the API. The patch
> implements the 2.4 Nova API microversion, though, as you can see from
> this part of the patch:
> https://review.openstack.org/#/c/128940/43/nova/api/openstack/compute/plugins/v3/server_tags.py
> What is the point of creating a new "plugin"/API extension for this new
> functionality? Why can't we just modify the
> nova/api/openstack/compute/server.py Controller.show() method and
> decorate it with a 2.4 microversion that adds a "tags" attribute to the
> returned server dictionary?
> https://github.com/openstack/nova/blob/master/nova/api/openstack/compute/servers.py#L369
> Because we're using an API extension for this new server tags
> functionality, we are instead having the extension "extend" the server
> dictionary with an "os-server-tags:tags" key containing the list of
> string tags.
> This is ugly and pointless. We don't need to use API extensions any more
> for this stuff.
> A client knows that server tags are supported by the 2.4 API
> microversion. If the client requests the 2.4+ API, then we should just
> include the "tags" attribute in the server dictionary.
> Similarly, new microversion API functionality should live in a module,
> as a top-level (or subcollection) Controller in
> /nova/api/openstack/compute/, and should not be in the
> /nova/api/openstack/compute/plugins/ directory. Why? Because it's not a
> plugin.
> Why are we continuing to use these awkward, messy, and cumbersome API
> extensions?
> Please, I am begging the Nova core team. Let us stop this madness. No
> more API extensions.
> Best,
> -jay
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