[feature request] allow to filter by label value in TcpDiscoveryKubernetesIpFinder

[vanrenter]

I use Ignite in production within a kubernetes cluster. I use the TcpDiscoveryKubernetesIpFinder and it works great. I must also add that I embark ignite servers within my app, in the same java process. All this works great except for one thing:

• I restart my app (let's call it my-app), the cache is "persisted" and not restarted from scratch (I will explain the process below)

That can be a perfectly valid use case, but in my case I would prefer the cache to be restarted when my application restarts. Here are the reasons:

• I real production life, sometimes the data (that are cached) are changed directly in a third party app or database, and did not occur within my-app. If the cache is not restarted, I am missing these changes "forever"
• my-app is far from perfect and it can happen that a change hits the backend, but is not reflected in the Ignite cache (my fault, not Ignite fault)
• I cache java objects in Ignite. If the structure of these java object is changed in some release of my-app, I am afraid that incoherence with the cached values with definition n-1 causes problem with my-app version n.

The solution I could imagine to solve the problem would be the following:

• In the kubernetes discovery, allow to pass a kubernetes "label" and optionnally a "label value"
• then, filter all the pods found to those that have the same label value as the current one (or that matches exactly label=label-value, which would do pretty much the same)
• In my kubernetes config, I am thinking to the following label, that is incremented at each deployment of my-app : "labels/deployment"

I must say that there is a workaround to what I describe above to force the cache to be restarted : change the "strategy type" to recreate . Kubernetes will then kill all the "old" pods before starting the first new pod. That works, but causes an interruption in service

I am now giving the example of why the cache is "persisted" through a restart

• pre restart, I have the folloing pods ** my-app-abc (labels/deployment=my-app-123) ** my-app-def (labels/deployment=my-app-123) ** my-app-ghi (labels/deployment=my-app-123) ** all of these three pods are in the Ignite cluster
• I restart the app with kubernetes, kubernetes does the following : it creates a new po ** my-app-jkl (labels/deployment=my-app-124) ** so this pod also joins the Ignite cluster, gets all the entries, .. etc
• Then, kubernetes kill stop all pods of version 123 and start new pods of version 124
• So I guess, you get the point. The fact that pods of version 124 and 123 are "alive" at the same time will make the cache "persistent" to a restart of my-app