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)
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