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]. * Maybe we could perform discovery using this mechanism? I'm aware of
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.
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-serv ices
[5] http://kubernetes.io/docs/user-guide/petset/#peer-discovery
[6] https://gist.github.com/slaskawi/0866e63a39276f8ab6637622971 6a676
[7] https://github.com/jboss-openshift/openshift-ping/tree/maste r/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/7cffb5588dabb770f654557579c 5f2d0
--
Bela Ban, JGroups lead (http://www.jgroups.org)