DevOps Classroomnotes 10/Sep/2023


  • Pod tries to keep containers running, but for us we need to keep Pods running according to some state, Lets understand first two categories
    • Replicas:
      • Here we have two resources ReplicationController, ReplicaSet
      • Here our desired state (spec) will be
        • number of replicas
        • pod spec
        • label selector
      • These objects try maintain the desired
    • Jobs:
      • These will run the Pods which have finite execution time period
      • Here we have two resources
        • Job
        • CronJob


  • This Resource is responsible for maintaing the desired state of number of replicase of pod
  • Refer Here for official docs


  • Create a replica set with 3 replicas of jenkins/jenkins
  • Refer Here for the manifests
  • Lets try set based selectors Refer Here for the changes
  • Exercise: Write a Replication controller for creating 3 httpd pods

Jobs and Cron Jobs

  • Refer Here for Offical jobs documentation and Refer Here for Official CronJob Documentation
  • Lets write a Cron Job which runs alpine pod with some script for every 5 mins
  • Refer Here for the changes


  • Namespace in k8s is a logical space or logical cluster in which resources will be created
  • Any resource which has a value of Namespace = true belongs in a namespace and with Namespace=false is shared across namespaces.
  • Refer Here for official docs

Service in K8s

  • Every Pod when created gives a unique ip address and Name
  • When Pods are scaled
  • Lets create a replicaset with 3 nginx pods with label app:nginx
apiVersion: apps/v1
kind: ReplicaSet
  name: nginx-rs
    app: nginx
    purpose: svcdemo
  replicas: 3
  minReadySeconds: 1
      app: nginx
        app: nginx
        - name: nginxc
          image: nginx:1.25
            - containerPort: 80
              protocol: TCP
  • We need to access nginx with in cluster, but pod ips are not reliable, so as shown in the below image, lets create a k8s service resource which gives a consistent ip and name to access all the pods matching labels (equality based selection)
  • service in k8s is of 4 types
    • Cluster IP: This gives an ipaddress or name which can be accessed with in cluster
    • None: TBD
    • External: TBD
    • LoadBalancer: TBD
  • Refer Here for the changeset
  • Lets create nginx rs and and service and view endpoints. As discussed in the class when pods get update the endpoints are reflected. Service will forward the requests to endpoints
  • We will try correcting the access issue and external access in the next session

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