Replicaset Link to heading

Replicasets are a fun topic…this new object replaces the old “Replication Controller”. Replicaset (shortname “rs”) can control pods that are not created within the replicaset or other deployment by simply matching labels.

Details Link to heading

• a single pod crashes then loses access to app - idea to have more than one instance of a pod
• another reason - to create multiple pods to share the load and balance
• spans across multiple nodes
• scales when demand increases

Setup Link to heading

• create YAML
• use 4 top level objects - api/kind/metadata/spec
• create POD template section under SPEC
• to create POD template MOVE the normal fields: metadata, name, labels and spec…usually defined in POD
• move thos fields under spec.template

ReplicaSet Link to heading

apiVersion:  apps/v1
kind:  ReplicaSet
metadata:
  name: my-replicaset
  labels:
     app:  myapp
     type: frontend
spec:
  template:
    metadata:
      name: myapp-pod
      labels:
        app:  myapp
        type: frontend
    spec:
      containers:
      -  name:  nginx-container
         image: nginx
  replicas: 3
  selector:
    matchLabels:
      type: frontend

• ReplicaSet can handle other pods that haven’t been created under the yaml file
• SELECTOR is the difference for the ReplicaSet
• MUST use selector.matchLabels

Labels and Selectors Link to heading

• use to monitor existing pods is one use case
• role of replicaSet is to monitor and deploy if any fail
• use same label set in “MatchLabels” and it knows which pods
• spec.replicas
• spec.selector.matchLabels.type

Scale Link to heading

• increase REPLICAS

1st method update number of replica field in definition file then use REPLACE cmd kubectl replace -f replica-set.yaml

2nd method use SCALE cmd kubectl scale --replicas=6 -f replica-set.yaml

3rd method also scale cmd but use resource TYPE and resource NAME fields from definition file in command kubectl scale --replicas=6 -f replicaset myapp-replicaset

Commands Link to heading

kubectl create -f replica-set.yaml

kubectl get replicaset

kubectl delete replicaset myapp-replicaset

kubectl replace -f replica-set.yaml

kubectl scale -replicas=6 -f replicaset-definition.yaml

k explain replicaset myapp-replicaset