[openstack-dev] [Openstack-operators] [nova][glance] Who needs multiple api_servers?
Eric Fried
openstack at fried.cc
Fri Apr 28 16:19:35 UTC 2017
If it's *just* glance we're making an exception for, I prefer #1 (don't
deprecate/remove [glance]api_servers). It's way less code &
infrastructure, and it discourages others from jumping on the
multiple-endpoints bandwagon. If we provide endpoint_override_list
(handwave), people will think it's okay to use it.
Anyone aware of any other services that use multiple endpoints?
On 04/28/2017 10:46 AM, Mike Dorman wrote:
> Maybe we are talking about two different things here? I’m a bit confused.
>
> Our Glance config in nova.conf on HV’s looks like this:
>
> [glance]
> api_servers=http://glance1:9292,http://glance2:9292,http://glance3:9292,http://glance4:9292
> glance_api_insecure=True
> glance_num_retries=4
> glance_protocol=http
>
> So we do provide the full URLs, and there is SSL support. Right? I am fairly certain we tested this to ensure that if one URL fails, nova goes on to retry the next one. That failure does not get bubbled up to the user (which is ultimately the goal.)
>
> I don’t disagree with you that the client side choose-a-server-at-random is not a great load balancer. (But isn’t this roughly the same thing that oslo-messaging does when we give it a list of RMQ servers?) For us it’s more about the failure handling if one is down than it is about actually equally distributing the load.
>
> In my mind options One and Two are the same, since today we are already providing full URLs and not only server names. At the end of the day, I don’t feel like there is a compelling argument here to remove this functionality (that people are actively making use of.)
>
> To be clear, I, and I think others, are fine with nova by default getting the Glance endpoint from Keystone. And that in Keystone there should exist only one Glance endpoint. What I’d like to see remain is the ability to override that for nova-compute and to target more than one Glance URL for purposes of fail over.
>
> Thanks,
> Mike
>
>
>
>
> On 4/28/17, 8:20 AM, "Monty Taylor" <mordred at inaugust.com> wrote:
>
> Thank you both for your feedback - that's really helpful.
>
> Let me say a few more words about what we're trying to accomplish here
> overall so that maybe we can figure out what the right way forward is.
> (it may be keeping the glance api servers setting, but let me at least
> make the case real quick)
>
> From a 10,000 foot view, the thing we're trying to do is to get nova's
> consumption of all of the OpenStack services it uses to be less special.
>
> The clouds have catalogs which list information about the services -
> public, admin and internal endpoints and whatnot - and then we're asking
> admins to not only register that information with the catalog, but to
> also put it into the nova.conf. That means that any updating of that
> info needs to be an API call to keystone and also a change to nova.conf.
> If we, on the other hand, use the catalog, then nova can pick up changes
> in real time as they're rolled out to the cloud - and there is hopefully
> a sane set of defaults we could choose (based on operator feedback like
> what you've given) so that in most cases you don't have to tell nova
> where to find glance _at_all_ becuase the cloud already knows where it
> is. (nova would know to look in the catalog for the interal interface of
> the image service - for instance - there's no need to ask an operator to
> add to the config "what is the service_type of the image service we
> should talk to" :) )
>
> Now - glance, and the thing you like that we don't - is especially hairy
> because of the api_servers list. The list, as you know, is just a list
> of servers, not even of URLs. This means it's not possible to configure
> nova to talk to glance over SSL (which I know you said works for you,
> but we'd like for people to be able to choose to SSL all their things)
> We could add that, but it would be an additional pile of special config.
> Because of all of that, we also have to attempt to make working URLs
> from what is usually a list of IP addresses. This is also clunky and
> prone to failure.
>
> The implementation on the underside of the api_servers code is the
> world's dumbest load balancer. It picks a server from the list at
> random and uses it. There is no facility for dealing with a server in
> the list that stops working or for allowing rolling upgrades like there
> would with a real load-balancer across the set. If one of the API
> servers goes away, we have no context to know that, so just some of your
> internal calls to glance fail.
>
> Those are the issues - basically:
> - current config is special and fragile
> - impossible to SSL
> - unflexible/unpowerful de-facto software loadbalancer
>
> Now - as is often the case - it turns out the combo of those things is
> working very well for you -so we need to adjust our thinking on the
> topic a bit. Let me toss out some alternatives and see what you think:
>
> Alternative One - Do Both things
>
> We add the new "consume from catalog" and make it default. (and make it
> default to consuming the internal interface by default) We have to do
> that in parallel with the current glance api_servers setting anyway,
> because of deprecation periods, so the code to support both approaches
> will exist. Instead of then deprecating the api_servers list, we keep
> it- but add a big doc warning listing the gotchas and limitations - but
> for those folks for whom they are not an issue, you've got an out.
>
> Alternative Two - Hybrid Approach - optional list of URLs
>
> We go ahead and move to service config being the standard way one lists
> how to consume a service from the catalog. One of the standard options
> for consuming services is "endpoint_override" - which is a way an API
> user can say "hi, please to ignore the catalog and use this endpoint
> I've given you instead". The endpoint in question is a full URL, so
> https/http and ports and whatnot are all handled properly.
>
> We add, in addition, an additional option "endpoint_override_list" which
> allows you to provide a list of URLs (not API servers) and if you
> provide that option, we'll keep the logic of choosing one at random at
> API call time. It's still a poor load balancer, and we'll still put
> warnings in the docs about it not being a featureful load balancing
> solution, but again would be available if needed.
>
> Alternative Three - We ignore you and give you docs
>
> I'm only including this because in the name of completeness. But we
> could write a bunch of docs about a recommended way of putting your
> internal endpoints in a load balancer and registering that with the
> internal endpoint in keystone. (I would prefer to make the operators
> happy, so let's say whatever vote I have is not for this option)
>
> Alternative Four - We update client libs to understand multiple values
> from keystone for endpoints
>
> I _really_ don't like this one - as I think us doing dumb software
> loadbalancing client side is prone to a ton of failures. BUT - right now
> the assumption when consuming endpoints from the catalog is that one and
> only one endpoint will be returned for a given
> service_type/service_name/interface. Rather than special-casing the
> url roundrobin in nova, we could move that round-robin to be in the base
> client library, update api consumption docs with round-robin
> recommendations and then have you register the list of endpoints with
> keystone.
>
> I know the keystone team has long been _very_ against using keystone as
> a list of all the endpoints, and I agree with them. Putting it here for
> sake of argument.
>
> Alternative Five - We update keystone to round-robin lists of endpoints
>
> Potentially even worse than four and even more unlikely given the
> keystone team's feelings, but we could have keystone continue to only
> return one endpoint, but have it do the round-robin selection at catalog
> generation time.
>
>
> Sorry - you caught me in early morning brainstorm mode.
>
> I am neither nova core nor keystone core. BUT:
>
> I think honestly if adding a load balancer in front of your internal
> endpoints is an undue burden and/or the usefulness of the lists
> outweighs the limitations they have, we should go with One or Two. (I
> think three through five are all terrible)
>
> My personal preference would be for Two - the round-robin code winds up
> being the same logic in both cases, but at least in Two folks who want
> to SSL all the way _can_, and it shouldn't be an undue extra burden on
> those of you using the api_servers now. We also don't have to do the
> funky things we currently have to do to turn the api_severs list into
> workable URLs.
>
>
> On 04/27/2017 11:50 PM, Blair Bethwaite wrote:
> > We at Nectar are in the same boat as Mike. Our use-case is a little
> > bit more about geo-distributed operations though - our Cells are in
> > different States around the country, so the local glance-apis are
> > particularly important for caching popular images close to the
> > nova-computes. We consider these glance-apis as part of the underlying
> > cloud infra rather than user-facing, so I think we'd prefer not to see
> > them in the service-catalog returned to users either... is there going
> > to be a (standard) way to hide them?
> >
> > On 28 April 2017 at 09:15, Mike Dorman <mdorman at godaddy.com> wrote:
> >> We make extensive use of the [glance]/api_servers list. We configure that on hypervisors to direct them to Glance servers which are more “local” network-wise (in order to reduce network traffic across security zones/firewalls/etc.) This way nova-compute can fail over in case one of the Glance servers in the list is down, without putting them behind a load balancer. We also don’t run https for these “internal” Glance calls, to save the overhead when transferring images.
> >>
> >> End-user calls to Glance DO go through a real load balancer and then are distributed out to the Glance servers on the backend. From the end-user’s perspective, I totally agree there should be one, and only one URL.
> >>
> >> However, we would be disappointed to see the change you’re suggesting implemented. We would lose the redundancy we get now by providing a list. Or we would have to shunt all the calls through the user-facing endpoint, which would generate a lot of extra traffic (in places where we don’t want it) for image transfers.
> >>
> >> Thanks,
> >> Mike
> >>
> >>
> >>
> >> On 4/27/17, 4:02 PM, "Matt Riedemann" <mriedemos at gmail.com> wrote:
> >>
> >> On 4/27/2017 4:52 PM, Eric Fried wrote:
> >> > Y'all-
> >> >
> >> > TL;DR: Does glance ever really need/use multiple endpoint URLs?
> >> >
> >> > I'm working on bp use-service-catalog-for-endpoints[1], which intends
> >> > to deprecate disparate conf options in various groups, and centralize
> >> > acquisition of service endpoint URLs. The idea is to introduce
> >> > nova.utils.get_service_url(group) -- note singular 'url'.
> >> >
> >> > One affected conf option is [glance]api_servers[2], which currently
> >> > accepts a *list* of endpoint URLs. The new API will only ever return *one*.
> >> >
> >> > Thus, as planned, this blueprint will have the side effect of
> >> > deprecating support for multiple glance endpoint URLs in Pike, and
> >> > removing said support in Queens.
> >> >
> >> > Some have asserted that there should only ever be one endpoint URL for
> >> > a given service_type/interface combo[3]. I'm fine with that - it
> >> > simplifies things quite a bit for the bp impl - but wanted to make sure
> >> > there were no loudly-dissenting opinions before we get too far down this
> >> > path.
> >> >
> >> > [1]
> >> > https://blueprints.launchpad.net/nova/+spec/use-service-catalog-for-endpoints
> >> > [2]
> >> > https://github.com/openstack/nova/blob/7e7bdb198ed6412273e22dea72e37a6371fce8bd/nova/conf/glance.py#L27-L37
> >> > [3]
> >> > http://eavesdrop.openstack.org/irclogs/%23openstack-keystone/%23openstack-keystone.2017-04-27.log.html#t2017-04-27T20:38:29
> >> >
> >> > Thanks,
> >> > Eric Fried (efried)
> >> > .
> >> >
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> >>
> >> +openstack-operators
> >>
> >> --
> >>
> >> Thanks,
> >>
> >> Matt
> >>
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