Open Stack

On 02/04/2014 11:09 AM, Dean Troyer wrote:
> On Tue, Feb 4, 2014 at 9:00 AM, Sean Dague <sean at dague.net 
> <mailto:sean at dague.net>> wrote:
>
>     Can you be more specific about what goes wrong here? I'm not entirely
>     sure I understand why an old client of arbitrary age needs to be
>     supported with new OpenStack. The contract is the API, not the client,
>     and an old client that doesn't do version discovery is just a buggy
>     client from what I'm concerned. Time to release a new version.
>
>

Remember:  the client is not the only code that Keystone has to worry 
about.  THere is also a whole cotteage industry that is talking direct 
to the endpoints themselves.  We've trained these poor souls to expect 
the version in the Endpoint.  So even if we said "we are only supporting 
the latest  Keystone client"  we'd still have to deal with code that 
expects the identity endpoint URL to look like this:

https://hostname:35357/v2.0/

We want people to be able to call on the V3 API.  To be able to do 
version discovery, the identity endpoint URL should look like this:

https://hostname:35357/

And then they can navigate down to

https://hostname:35357/v3

Via discovery.  So, what I am proposing for Keystone (here: 
https://review.openstack.org/#/c/62801/)  is that we do this

If the Catalog endpoint looks like this: https://hostname:35357/v2.0/  
chop off /v2.0  and call on it for discover.

Now, the code In that link *will* work the same on a 
https://hostname:35357/v3/  due to the regex (copied from termie who 
recognized this problem long ago)  and that may scare you into saying 
"won't we have this problem in the future?"

Maybe, if we are stupid.  We've been stupid before, so I can't promise 
anything.  However,  much more important is that, as the tools for 
deployment get smarter, they stop putting out Service catalogs with 
versions in the URLS.  They would have to deliberately replace an 
explicit /v3 into the url in place of the V2.0  Then, yes, the hack 
would still silently work.

But without the hack, if they only check against the the V3 API, it will 
still work, too.  Broken again, and we are back here....this really is 
something that requires education across the deployers.




> Problem 1: API version discovery is not universally considered to be 
> part of the API and therefore is not defined by most services beyond 
> them responding to a '/' request with a 300 response and a list of 
> versions. No two of these responses look alike except where the source 
> was copied from an existing service.
>
> Problem 2: Identity is unique in that it is handed a 
> deployment-defined URL to authenticate and get endpoints for all other 
> services.  Most of these auth URLs have a version hard-coded in them 
> because the client didn't do version discovery or negotiation until 
> recently.  This is what we're talking about here, how to remove the 
> version from this URL and not break old clients.  We can't.  Not 
> without doing nasty things like detecting an old client and 
> compensating for it server-side.  So we have to work out a way for new 
> clients to do discovery even when handed a URL that has a version in it.
>
> I've tested a couple of more generalized approaches, and the best 
> solution I have found so far is to simply special-case the known 
> legacy behaviour then drop in to the general discovery process.
>
>     I also wonder if this is an issue with version discovery
>     implementation.
>     It seems like if we think this is going to be affecting multiple
>     services before doing an odd hack for keystone, we should actually
>     figure out a pattern that works for all services, and figure out why
>     this has only just become an issue. Most of the other services
>     have done
>
>
> The services that traditionally embed a version inside the URL 
> followed by a tenant ID or something get even deeper into parsing the 
> URL to hack the version.
>
>     dual APIs at some point over the last 2 years, and this didn't seem to
>     trip them up too badly. What happened differently in keystone that
>     made
>     this an issue? And what can be learned about how we structure APIs
>     going
>     forward.
>
>
> I think the difference is this is the first API we have actually tried 
> to deprecate and we don't have the option to hide it in an updated SC 
> endpoint.  The service catalog has hidden a lot of this pain for other 
> services because the clients generally can use whatever endpoint the 
> SC gives it.
>
>
> a) Version discovery needs to be rationalized across the services. 
>  We've talked about this at summits before, and proposals have been 
> written.  And here we are.  We'll do it again in Atlanta, hopefully 
> for the last time.
>
> b) Define a common structured endpoint and let the client assemble the 
> components into the final URL.  If the service catalog had a base URL 
> for compute, and a list of versions, and the additional bits to be 
> appended the client could make an intelligent choice and assemble the 
> endpoint.  It isn't like the client doesn't already have to know how 
> the REST URLs are constructed.
>
> b-alt) Stop putting things like tenant IDs in the SC.  This has the 
> same issue as the auth URL in how to do this without instantly 
> breaking the existing clients.
>
> dt
>
> -- 
>
> Dean Troyer
> dtroyer at gmail.com <mailto:dtroyer at gmail.com>
>
>
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