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Kubernetes Controllers

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Recommended Reads: Kubernetes - Objects & Resources

Controllers

  • Controllers are managed by k8s kube controller manager which is a core component of k8s.
    • Each controller tries to move the current cluster state closer to the desired state.
  • Almost every Kubernetes object includes two nested object fields that govern the object’s configuration: the object spec and the object status.
    • The spec describes the desired state of the object, providing a description of the characteristics you want the resource to have.
    • The status describes the current state of the object, supplied and updated by the Kubernetes system and its components.
  • In Kubernetes, controllers are control loops that watch the state of your cluster, then make or request changes where needed.
    • attachments/Pasted image 20230508142255.jpg
    • In simple words controller is a program which is running on our k8s cluster and trying to match the current state with the expected state.
  • An example where we would want to use a custom controller
    • Suppose we have a number of namespaces and we create a secret in one of the namespaces.
    • Since secrets are namespaced objects, if we want to create the same secret in all the namespaces then we will have to do it manually.
    • Instead we can create a custom controller which looks for secrets in any namespace and then creates it in all the namespaces.

References

Last updated: 2023-05-15