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Kubernetes – Replica Sets

Replica Set ensures how many replica of pod should be running. It can be considered as a replacement of replication controller. The key difference between the replica set and the replication controller is, the replication controller only supports equality-based selector whereas the replica set supports set-based selector.

apiVersion: extensions/v1beta1 --------------------->1
kind: ReplicaSet --------------------------> 2
metadata:
   name: Tomcat-ReplicaSet
spec:
   replicas: 3
   selector:
      matchLables:
         tier: Backend ------------------> 3
      matchExpression:
{ key: tier, operation: In, values: [Backend]} --------------> 4
template:
   metadata:
      lables:
         app: Tomcat-ReplicaSet
         tier: Backend
      labels:
         app: App
         component: neo4j
   spec:
      containers:
      - name: Tomcat
      image: tomcat: 8.0
      ports:
      - containerPort: 7474

Setup Details

  • apiVersion: extensions/v1beta1 → In the above code, the API version is the advanced beta version of Kubernetes which supports the concept of replica set.
  • kind: ReplicaSet → We have defined the kind as the replica set which helps kubectl to understand that the file is used to create a replica set.
  • tier: Backend → We have defined the label tier as backend which creates a matching selector.
  • {key: tier, operation: In, values: [Backend]} → This will help matchExpression to understand the matching condition we have defined and in the operation which is used by matchlabel to find details.

Run the above file using kubectl and create the backend replica set with the provided definition in the yaml file.

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