DevOps Classroom Series – 12/Feb/2020


  • Replica Set:

    • Much like Replication Controller
    • Replica Set can be preserved and revisited
  • Stateful Sets: For easier understanding,

    • Stateful Sets are much like Replication Controllers with persistent storage
    • note: This definition is not 100% right, but its ok for now
  • Jobs & Cron Jobs:

    • Job/Cron Job speaks about specification which will run some application/script/code which will execute and finish
  • Note:

    • Like any other k8s object, Controllers also have
      • Specification
      • Status
    • Here the Specification is more about controlling the objects/workloads.
      • Can define workload
      • how to manage the workload


  • Consider this Scenario, where we have app server and db server Preview

  • In this app server will communicate with db server to store/retrieve the data

  • Now due to application load you have scaled pods to 3 Preview

  • Now lets assume the node on which mysql pod is running has failed, In that case we get a new sql pod which has new ip address Preview

  • In this case application stops working as db is not connected.

  • To Resolve this , K8s uses Service which is used for communicating to the database pod. Preview

  • Now lets assume pod has failed and new mysql pod is created

  • When a service is created, in the specification label information has to be provided.

  • K8s service will forward traffic to the pods matching the labels given in the service spec Preview

  • Service is a Layer-4 load balancer

  • In K8s layer-7 load balancing is supported by ingress.

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