[infinispan-dev] Infinispan and OpenShift/Kubernetes PetSets
Bela Ban
bban at redhat.com
Sat Aug 20 03:19:12 EDT 2016
If we add a DNS discovery protocol, it would only be another discovery
protocol among many, and customers can choose which one to use.
I'm also thinking of adding the ability to JGroups to use multiple
discovery protocols in the same stack and combine their result sets into
one. Not sure though if it makes sense to use KUBE_PING and DNS in the
same stack...
On 20/08/16 00:04, Rob Cernich wrote:
> A couple of things...
>
> re. volumes:
> We also need to consider the mounting behavior for scale down scenarios
> and for overage scenarios when doing upgrades. For the latter,
> OpenShift can spin up pods of the new version before the older version
> pods have terminated. This may mean that some volumes from the old pods
> are orphaned. We did see this when testing A-MQ during upgrades. With
> a single pod, the upgrade process caused the new version to have a new
> mount and the original mount was left orphaned (another upgrade would
> cause the newer pod to pick up the orphaned mount, leaving the new mount
> orphaned). I believe we worked around this by specifying an overage of
> 0% during upgrades. This ensured the new pods would pick up the volumes
> left behind by the old pods. (Actually, we were using subdirectories in
> the mount, since all pods shared the same volume.)
>
> re. dns:
> DNS should work fine as-is, but there are a couple things that you need
> to consider.
> 1. Service endpoints are only available in DNS after the pod becomes
> ready (SVC records on the service name). Because infinispan attaches
> itself to the cluster, this meant pods were all started as cluster of
> one, then merged once they noticed the other pods. This had a
> significant impact on startup. Since then, OpenShift has added the
> ability to query the endpoints associated with a service as soon as the
> pod is created, which would allow initialization to work correctly. To
> make this work, we'd have to change the form of the DNS query to pick up
> the service endpoints (I forget the naming scheme).
>
> Another thing to keep in mind is that looking up pods by labels allows
> any pod with the specified label to be added to the cluster. I'm not
> sure of a use case for this, but it would allow other deployments to be
> included in the cluster. (You could also argue that the service is the
> authority for this and any pod with said label would be added as a
> service endpoint, thus achieving the same behavior...probably more
> simply too.)
>
> Lastly, DNS was a little flaky when we first implemented this, which was
> part of the reason we went straight to kubernetes. Users were using
> dnsmasq with wildcards that worked well for routes, but ended up routing
> services to the router ip instead of pod ip. Needless to say, there
> were a lot of complications trying to use DNS and debug user problems
> with service resolution.
>
> Hope that helps,
> Rob
>
> ------------------------------------------------------------------------
>
> Hey Bela!
>
> No no, the resolution can be done with pure JDK.
>
> Thanks
> Sebastian
>
> On Fri, Aug 19, 2016 at 11:18 AM, Bela Ban <bban at redhat.com
> <mailto:bban at redhat.com>> wrote:
>
> Hi Sebastian
>
> the usual restrictions apply: if DNS discovery depends on
> external libs, then it should be hosted in jgroups-extras,
> otherwise we can add it to JGroups itself.
>
> On 19/08/16 11:00, Sebastian Laskawiec wrote:
>
> Hey!
>
> I've been playing with Kubernetes PetSets [1] for a while
> and I'd like
> to share some thoughts. Before I dig in, let me give you
> some PetSets
> highlights:
>
> * PetSets are alpha resources for managing stateful apps
> in Kubernetes
> 1.3 (and OpenShift Origin 1.3).
> * Since this is an alpha resource, there are no
> guarantees about
> backwards compatibility. Alpha resources can also be
> disabled in
> some public cloud providers (you can control which API
> versions are
> accessible [2]).
> * PetSets allows starting pods in sequence (not relevant
> for us, but
> this is a killer feature for master-slave systems).
> * Each Pod has it's own unique entry in DNS, which makes
> discovery
> very simple (I'll dig into that a bit later)
> * Volumes are always mounted to the same Pods, which is
> very important
> in Cache Store scenarios when we restart pods (e.g.
> Rolling Upgrades
> [3]).
>
> Thoughts and ideas after spending some time playing with
> this feature:
>
> * PetSets make discovery a lot easier. It's a combination
> of two
> things - Headless Services [4] which create multiple A
> records in
> DNS and predictable host names. Each Pod has it's own
> unique DNS
> entry following pattern:
> {PetSetName}-{PodIndex}.{ServiceName} [5].
> Here's an example of an Infinispan PetSet deployed on
> my local
> cluster [6]. As you can see we have all domain names
> and IPs from a
> single DNS query.
> * Maybe we could perform discovery using this mechanism?
> I'm aware of
> DNS discovery implemented in KUBE_PING [7][8] but the
> code looks
> trivial [9] so maybe it should be implement inside
> JGroups? @Bela -
> WDYT?
> * PetSets do not integrate well with OpenShift 'new-app'
> command. In
> other words, our users will need to use provided yaml
> (or json)
> files to create Infinispan cluster. It's not a
> show-stopper but it's
> a bit less convenient than 'oc new-app'.
> * Since PetSets are alpha resources they need to be
> considered as
> secondary way to deploy Infinispan on Kubernetes and
> OpenShift.
> * Finally, the persistent volumes - since a Pod always
> gets the same
> volume, it would be safe to use any file-based cache store.
>
> If you'd like to play with PetSets on your local
> environment, here are
> necessary yaml files [10].
>
> Thanks
> Sebastian
>
>
> [1] http://kubernetes.io/docs/user-guide/petset/
> [2] For checking which APIs are accessible, use 'kubectl
> api-versions'
> [3]
> http://infinispan.org/docs/stable/user_guide/user_guide.html#_Rolling_chapter
> [4]
> http://kubernetes.io/docs/user-guide/services/#headless-services
> [5] http://kubernetes.io/docs/user-guide/petset/#peer-discovery
> [6]
> https://gist.github.com/slaskawi/0866e63a39276f8ab66376229716a676
> [7]
> https://github.com/jboss-openshift/openshift-ping/tree/master/dns
> [8]
> https://github.com/jgroups-extras/jgroups-kubernetes/tree/master/dns
> [9] http://stackoverflow.com/a/12405896/562699
> [10] You might need to adjust ImageStream.
> https://gist.github.com/slaskawi/7cffb5588dabb770f654557579c5f2d0
>
>
> --
> Bela Ban, JGroups lead (http://www.jgroups.org)
>
>
>
--
Bela Ban, JGroups lead (http://www.jgroups.org)
More information about the infinispan-dev
mailing list