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.
Unfortunately, it's not, but I don't think it's due to a Heat problem so
much as just the nature of the issue. Here's what's happening.
New Client: doesn't do client-side environment resolution before sending
it to the server.
Old Server: expects the environment to be fully populated and ignores
the environment file(s) in the files dict.
The result is the server spits back an error saying that, in my
scenario, there is no type mapping for jdob::Resource1.
The problem is, I get the exact same result for New Client + New Server
+ incomplete environment files.
The reason I was looking for some sort of version checking is to avoid
having logic that just says "Maybe it's because it's an old server,
lemme resolve the environments and send the request again." It feels
really wrong to trigger two create requests when it's the templates
themselves that are wrong.
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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