On Fri, Aug 19, 2016 at 10:18 AM, Bela Ban <b...@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.
>
Bela, you forgot to mention an extra restriction: even if it has no
external deps, it should
not be too big in terms of LOC (what is the threshold?) ;)
Gustavo
>
> 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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