[Cloud] 4. Kubernetes Replicaset deployment

As the controllers to manage Pods in a kubernetes cluster, there are controllers named Deplotment and Replcaset. Among them, let's look at Rplicaset first.

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Replicaset is an improved version of the replica controller, and its main roles are as follows.

• Select the target Pod to manage using the Label value
• Control the number of operating pods of the selected Pods

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For example, after selecting a target pod by using the label selector value among dozens of pods in the cluster, it continuously monitors and creates a new pod when a pod fails and deletes the failed Pod while maintaining the service.

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Then, create a replacset directory under the test directory, create a yaml file, enter the following content into the file, save it, and then run the distribution.

root@master-VirtualBox:~/test# mkdir replicaset root@master-VirtualBox:~/test# cd replicaset/ root@master-VirtualBox:~/test# mkdir replicaset root@master-VirtualBox:~/test# cd replicaset/ root@master-VirtualBox:~/test/replicaset# vi replicaset.yaml apiVersion: apps/v1 kind: ReplicaSet ==> define deployed Object metadata: name: my-nginx labels: app: nginx ==> Label value of target Pod spec: replicas: 3 ==> quantity of Pod in Label selector: matchLabels: app: nginx template: metadata: labels: app: nginx spec: containers: - name: nginx image: nginx:1.10 ​ ​

Now, let's deploy and inquire the information of the deployed replicaset, and inquire the information of the Pod.

root@master-VirtualBox:~/test/replicaset# kubectl apply -f replicaset.yaml replicaset.apps/my-nginx created root@master-VirtualBox:~/test/replicaset# kubectl get replicasets NAME DESIRED CURRENT READY AGE my-nginx 3 3 0 32s root@master-VirtualBox:~/test/replicaset# kubectl get pods NAME READY STATUS RESTARTS AGE my-nginx-gblrg 1/1 Running 0 67s my-nginx-k2thq 1/1 Running 0 67s my-nginx-nfz4k 1/1 Running 0 67s

As shown in the information set in yaml above, you can see that 3 Pods have been deployed and all are in a normal state.

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Let's take a closer look at how replicaset works. Node1's Pod is different from Replicaset's Label value. Under the assumption that Pod B has the same label, if Node 1 fails. Pod B is recreated and operational on Node 2 by replicaset, but Pod A is not failover.

The figure below shows how replcest works in flowchart format.

• Find the Pod that has the same value as the Label and register it in the target list
• Compare the number of replica pods in YAML file with the number of Pods in operation
• The number of running Pods is small, creating a shortage
• If the number of running Pods is high, delete the excess

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