Open Stack

On 10/19/2016 05:32 PM, Brian Curtin wrote:
> I'm currently facing what looks more and more like an impossible
> problem in determining the root of each service on a given cloud. It
> is apparently a free-for-all in how endpoints can be structured, and I
> think we're out of ways to approach it that catch all of the ways that
> all people can think of.
>
> In openstacksdk, we can no longer use the service catalog for
> determining each service's endpoints. Among other things, this is due
> to a combination of some versions of some services not actually being
> listed, and with things heading the direction of version-less services
> anyway. Recently we changed to using the service catalog as a pointer
> to where services live and then try to find the root of that service
> by stripping the path down and making some extra requests on startup
> to find what's offered. Despite a few initial snags, this now works
> reasonably well in a majority of cases.
>
> We have seen endpoints structured in the following ways:
>  A. subdomains, e.g., https://service.cloud.com/v2
>  B. paths, e.g., https://cloud.com/service/v2 (sometimes there are
> more paths in between the root and /service/)
>  C. service-specific ports, e.g., https://cloud.com:1234/v2
>  D. both A and B plus ports
>
> Within all of these, we can find the root of the given service just
> fine. We split the path and build successively longer paths starting
> from the root. In the above examples, we need to hit the path just
> short of the /v2, so in B it actually takes two requests as we'd make
> one to cloud.com which fails, but then a second one to
> cloud.com/service gives us what we need.
>
> However, another case came up: the root of all endpoints is itself
> another service. That makes it look like this:
>
>  E. https://cloud.com:9999/service/v2
>  F. https://cloud.com:9999/otherservice
>
> In this case, https://cloud.com:9999 is keystone, so trying to get E's
> base by going from the root and outward will give me a versions
> response I can parse properly, but it points to keystone. We then end
> up building requests for 'service' that go to keystone endpoints and
> end up failing. We're doing this using itertools.accumulate on the
> path fragments, so you might think 'just throw it through
> `reversed()`' and go the other way. If we do that, we'll also get a
> versions response that we can parse, but it's the v2 specific info,
> not all available versions.
>
> So now that we can't reliably go from the left, and we definitely
> can't go from the right, how about the middle?
>
> This sounds ridiculous, and if it sounds familiar it's because they
> devise a "middle out" algorithm on the show Silicon Valley, but in
> most cases it'd actually work. In E above, it'd be fine. However,
> depending on the number of path fragments and which direction we chose
> to move first, we'd sometimes hit either a version-specific response
> or another service's response, so it's not reliable.
>
> Ultimately, I would like to know how something like this can be solved.
>
> 1. Is there any reliable, functional, and accurate programmatic way to
> get the versions and endpoints that all services on a cloud offer?

The Keystone service catalog should be the thing that provides the 
endpoints for all services in the cloud. Within each service, 
determining the (micro)version of the API is unfortunately going to be a 
per-service endeavour. For some APIs, a microversion header is returned, 
others don't have microversions. The microversion header is 
unfortunately not standardized for all APIs that use microversions, 
though a number of us would like to see a single:

OpenStack-API-Version: <service-type> <microversion>, ...

header supported. This is the header supported in the new placement REST 
API, for what it's worth.

> 2. Are there any guidelines, rules, expectations, or other
> documentation on how services can be installed and their endpoints
> structured that are helpful to people build apps that use them, not in
> those trying to install and operate them? I've looked around a few
> times and found nothing useful. A lot of what I've found has
> referenced suggestions for operators setting them up behind various
> load balancing tools.

I presume you are referring to the "internal" vs "public" endpoint 
stuff? If so, my preference has been that such "internal vs. external" 
routing should be handled via the Keystone service catalog returning a 
set of endpoints depending on the source (or X-forwarded-for) IP. So, 
requests from "internal" networks (for whatever definition of "internal" 
you want) return a set of endpoint URLs reflecting the "internal" endpoints.

> 3. If 1 and 2 won't actually help me solve this, do you have any other
> suggestions that will? We already go left, right, and middle of each
> URI, so I'm out of directions to go, and we can't go back to the
> service catalog.

I really don't understand why the service catalog should not be the 
thing that we use to catalog the... services. To me it seems obvious the 
Keystone service catalog is the focal point for what's needed here.

Best,
-jay