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

Christopher Yeoh cbkyeoh at gmail.com
Tue Mar 10 11:22:14 UTC 2015

On Mon, 09 Mar 2015 16:14:21 -0400
Sean Dague <sean at dague.net> wrote:

> On 03/09/2015 03:37 PM, Jay Pipes wrote:
> > On 03/08/2015 08:10 AM, Alex Xu wrote:
> >> Thanks for Jay point this out! If we have agreement on this and
> >> document it, that will be great for guiding developer how to add
> >> new API.
> >>
> >> I know we didn't want extension for API. But I think we still
> >> need modularity. I don't think we should put everything in a single
> >> file, that file will become huge in the future and hard to
> >> maintenance.
> > 
> > I don't think everything should be in a single file either. In fact,
> > I've never advocated for that.
> > 
> >> We can make the 'extension' not configurable. Replace 'extension'
> >> with another name, deprecate the extension info api int he
> >> future.... But that is not mean we should put everything in a file.
> > 
> > I didn't say that in my email. I'm not sure where you got the
> > impression I want to put everything in one file?
> > 
> >> For modularity, we need define what should be in a separated
> >> module(it is extension now.) There are three cases:
> >>
> >> 1. Add new resource
> >>      This is totally worth to put in a separated module.
> > 
> > Agreed.
> > 
> >> 2. Add new sub-resource
> >>      like server-tags, I prefer to put in a separated module, I
> >> don't think put another 100 lines code in the servers.py is good
> >> choice.
> > 
> > Agreed, which is exactly what I said in my email:
> > 
> > "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."
> > 

Ok so I'm getting confused about what we're disagreeing about then.

However, the first microversion change
https://review.openstack.org/#/c/140313/32 is one case where we didn't
need to create a new extension, relying only on microversions to add a
new parameter to the response, whereas server tags does add a new
conroller (os-server-tags) which is non trivia so I think it does. Do
we disagree about that?

btw in a situation now where (I think) we are saying we are not going
to do any work for 3rd parties to add their own API plugins and have a
well planned API we don't need the prefixes as we don't need the prefix
on parameter names as there won't be name clashes without us realising
during testing. And we certainly don't need the os- prefix is the
plugin alias, but we do neeed them unique across the API I believe
because of the way we store information about them.

> >> 3. extend attributes and methods for a existed resource
> >>     like add new attributes for servers, we can choice one of
> >> existed module to put it in. Just like this patch
> >> https://review.openstack.org/#/c/155853/
> >>     But for servers-tags, it's sub-resource, we can put it in
> >> its-own module.
> > 
> > Agreed, and that's what I put in my email.
> > 
> >> If we didn't want to support extension right now, we can begin
> >> from not show servers-tags in extension info API first. That means
> >> extension info is freeze now. We deprecated the extension info api
> >> in later version.

It can be surpressed from /extensions by adding it to the suppress list
in the extensions code. Probably a good idea to stop v2.1+microversion
code REST API users not accidentally relying on it.
> > 
> > I don't understand what you're saying here. Could you elaborate?
> > What I am asking for is for new functionality (like the server-tags
> > subcollection resource), just add a new module called
> > /nova/api/openstack/compute/server_tags.py, create a Controller
> > object in that file with the new server tags resource, and don't
> > use any of the API extensions framework whatsoever.
> > 
> > In addition to that, for the changes to the main GET
> > /servers/{server_id} resource, use microversions to decorate the
> > /nova/api/openstack/compute/servers.py.Controller.show() method for
> > 2.4 and add a "tags" key to the dict (note: NOT a
> > "os-server-tags:tags" key) returned by GET /servers/{server_id}. No
> > use of API extensions needed.

So I that's doabe but I think if we compared to the two wsgi.extends
is cleaner and less code and we have to have the separate module file
anyway for the controller. Can discuss this more later....

Incidentally as has been mentioned before we need new names for the
API and where the files need to live needs cleaning up. For example v3
and v2.1 needs to be worked out of the directory paths.This clenaup not
on involves but directly  affects the all the related unit and
functional tests. Nor should we have contrib or should v2 live directly
in in nova/api/openstack/compute. But we also need a name for v2.1
microversions and should spend some time on that (does api modules work
for anyone?)

I think this dicussion indicates we should start with a bit of planning
first rather than just jump in and start shuffling this around now.
Work out what we want the final thing to look like so we can see what
the dependencies look like and minimise the number of times that files
get shuffled around. It is also likely to be one of those patches that
is a real pain to merge without some well timed +2 coordination.

Perhaps its something we can talk about at the Nova API meeting this

Also, apologies in advance but over at least the next couple of weeks I
may be slow in replying on irc/email.  



> So possibly another way to think about this is our prior signaling of
> what was supported by Nova was signaled by the extension list. Our
> code was refactored into a way that supported optional loading by
> that unit.
> As we're making things less optional it probably makes sense to evolve
> the API code tree to look more like our REST resource tree. Yes, that
> means servers.py ends up being big, but it is less confusing that all
> servers related code is in that file vs all over a bunch of other
> files.
> So I'd agree that in this case server tags probably should just be in
> servers.py. I also think long term we should do some "plugin collapse"
> for stuff that's all really just features on one resource tree so that
> the local filesystem code structure looks a bit more like the REST
> url tree.
> 	-Sean

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