[Hawkular-dev] OpenShift Pet vs Cattle metaphor

[Matt Wringe]

----- Original Message -----
> From: "Jiri Kremser" <jkremser at redhat.com>
> To: "Discussions around Hawkular development" <hawkular-dev at lists.jboss.org>
> Sent: Thursday, 13 October, 2016 8:21:10 AM
> Subject: [Hawkular-dev] OpenShift Pet vs Cattle metaphor
> 
> Hello,
> today, I was on L&L about storage in OpenShift and I learn interesting thing.
> I always thought, that everything needs to be immutable and stateless and
> all the state needs to be handled by means of NFS persistent volumes.
> Luckily, there is a feature in Kubernetess (since 1.3) that allows the PODs
> to be treated as pets. It's called PetSet [1] and it assigns a unique ID
> (and persistent DNS record) to a POD that runs in this "mode".

For OpenShift, we would have moved to using PetSets for our Cassandra pod, but its not a fully supported feature yet. In the next version we will be moving over to using it.

It will make changing the cluster size for Cassandra nodes a lot easier once we can use this.

> 
> Common use-case for PetSet is a set of pods with a relational DBs that uses
> some kind of master-slave replication and slaves needs to know the master's
> address. But it can be used for anything. We can use the hostname as the
> feed id for instance.
> 
> I don't know how much this will be popular because it kind of defeats the
> purpose of immutable infrastructure but it can save us some work with the
> feed identity. And of course we need to support also the "normal" POD
> scenario.

PetSets are meant for clustering of pods which have persistent storage. If this is not your use case, what exactly are you trying to do? There may be better ways to handle it.

> 
> [1]: http://kubernetes.io/docs/user-guide/petset/
> 
> jk
> 
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