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 <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.
>
> 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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