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kuberneteskubernetes-podkubernetes-statefulset

How to schedule the first replica of a statefulset to a specific node

I have a StatefulSet with several replicas, for example 3 and multiple kubernetes Node in two zones.

I want to place the FIRST replica in the selected zone and the rest in the others zones.

  • mysts-0-0 < main_zone
  • mysts-0-1 < back_zone
  • mysts-0-2 < back_zone

Why the first one? Each pod is a database instance. Replication is configured between them. And by default the first node is master.

So I want to be able to influence where the first node is installed.

Solution

  • This is not supported in StatefulSet, as the Pod-template is identical for each replica.

    You might be able to achieve this by writing a custom scheduler. For inspiration, see this article for a custom scheduler for CockroachDB: A Custom Kubernetes Scheduler to Orchestrate Highly Available Applications