Introduce BackupBatch CRD

[tamalsaha]

We want to take coordinated backup of multiple workloads. So, this CRD will have a []BackupConfigurtion.

This can also issue preBackup & postBackup hooks. https://kubernetes.io/docs/tasks/configure-pod-container/attach-handler-lifecycle-event/#define-poststart-and-prestop-handlers

[tamalsaha]

Usecase: Imagine we want to take backup of a sharded mongodb database via VolumeSnapshotter. Each shard is managed by a different Statefulset. Also, some pre and post backup commands needs to be issued. So,

• A BackupBatch object is created and one BackupConfiguration (no schedule and paused) for each statefulset shard.
• Add a pre and post backup command to BackupBatch.
• At the schedule defined in BackupBatch, stash operator performs these steps:
  • execs prebackup command,
  • creates a BackupSession for each BackupConfiguration,
  • waits for all of them to complete and exec a post backup command.

[tamalsaha]

• How to not confuse users with BackupBlueprint with BackupBatch?
• How to support BackupBatch in BackupBlueprint?

[tamalsaha]

kubelet prober

• https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/prober/prober.go

[tamalsaha]

I have created a sample project to test the prober logic in kubelet.
https://github.com/tamalsaha/prober-demo

Things TODO:

• Implement ContainerCommandRunner using pod exec lib. https://github.com/tamalsaha/prober-demo/blob/master/runtime.go#L55