[Hawkular-dev] Rolling upgrades (on Kubernetes)

Hey, on Kubernetes a common use case (that has been demonstrated by Thomas and Juca recently) are rolling upgrades (blue/green, canary, ...) where a new version of a service comes into play, gets scaled up and when this is scaled up, the old version of the service gets scaled down and eventually disappears. It can also happen though that the new version is buggy and the previous version gets scaled up again to take the full load until a fix is available. We need to make sure to support those rolling upgrades and also the rollback to the previous version of a service. E.g. if a (No)Sql schema update happens in version N+1, a still running instance of version N must not break by it, when N+1 is rolling out while N is still active. Similarly when N+1 has upgraded the schema and the application gets rolled back to version N, it must still be able to cope with the upgraded schema version. Same applies to APIs, but this is something we have discussed and mastered in the past. We should perhaps investigate how we can automatically test this scenario in our Travis testing.