Kubernetes - Replication Controllers and Replica Sets 👯

Replica Sets are newer than Replication Controllers, and are the preferred way to manage Pods 😤

Description 👀

A Replica Set is a set of pods that are managed by a controller. It ensures that the specified number of pods are running at any given time. If a pod fails, the Replica Set will create a new one to replace it.

Why use Replica Sets 💭

They enable users to monitor pods, by labeling pods it will allow replica set to know which pods to monitor and provides a method to filter out pods thats are not part of the replica set.

Basic Commands 📝

• get list of replica sets

    kubectl get replicaset
  

• get descriptive information on the desired replica set

    kubectl describe replicaset <replica-set-name>
  

• edit the specified replica set

    kubectl edit replicaset <replica-set-name>
  

• scale replica set to the desired number of replicas

    kubectl replace -f <edited-yaml-file>
  

  or

    kubectl scale --replicas=<new-number-of-replicas> -f <yaml-file>
  

• delete specified replica set

    kubectl delete replicaset <replica-set-name>
  

Examples 🧩

• sample replication controller definition

    apiVersion: v1
    kind: ReplicationController
    metadata:
        name: myapp-rc
        labels:
            app: myapp
            type: front-end
    # most crucial for replication controller
    spec:
        template:
            # pod template for the replication controller
            metadata:
                name: myapp-pod
                labels:
                    app: myapp
                    type: front-end
            spec:
                containers:
                  - name: nginx-container
                    image: nginx
        replicas: 3
  

• sample replica set definition

    apiVersion: apps/v1
    kind: ReplicaSet
    metadata:
        name: myapp-rs
        labels:
            app: myapp
            type: front-end
    spec: 
        template:
            metadata:
                name: myapp-pod
                labels:
                    app: myapp
                    type: front-end
            spec:
                containers:
                  - name: nginx-container
                    image: nginx
        replicas: 3
        #  one of the major differences between replica controller and replica set
        selector: 
            matchLabels:
            type: front-end
  

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