On 04/01/16 15:53, Jay Dobies wrote:
I ran into an issue in a review about moving environment resolution from
client to server [1]. It revolves around clients being able to access
older versions of servers (that's a pretty simplistic description; see
[2] for the spec).

Before the holiday, Steve Hardy and I were talking about the
complications involved. In my case, there's no good way to differentiate
an older server from a legitimate error.

Hmmm, it's true that you'll likely just get a 400 error, but I'd hope that the error message is at least somewhat unique.

Since the API isn't versioned to the extent that we can leverage that

I mean... it totally is but so far we've chosen not to bump that version. And we mostly got away with it because we were only adding functionality. So far.

value, I was looking into using the template versions call. Something
along the lines of:

   supported_versions = hc.template_versions.list()
   version_nums = [i.to_dict()['version'].split('.')[1] for i in
supported_versions]
   mitaka_or_newer = [i for i in version_nums if i >= '2016-04-08']

Yes, I'm planning on cleaning that up before submitting it :)

What I'm wondering is if I should make this into some sort of
generalized utility method in the client, under the assumption that
we'll need this sort of check in the future for the same backward
compatibility requirements.

So a few questions:

1. Does anyone strongly disagree to checking supported template versions
as a way of determining the specifics of the server API.

Yes.

Template versions are supposed to be pluggable, and are explicitly under control of the operator. We shouldn't be systematically inferring anything about the server version based on this; in general there's no causal relationship.

2. Does anything like this already exist that I can use?

Not really; there's the "heat build-info" command, but that is also explicitly under the control of the operator (and is empty by default).

3. If not, any suggestions on where I should put it? I see a
heat.common.utils module but I'm not sure if there is a convention
against that module (or common in general) making live server calls.

Thanks :D


[1] https://review.openstack.org/#/c/239504/
[2] https://review.openstack.org/#/c/226157/

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