In the previous article, we introduced how to use NFS for file sharing and how to mount shared files in each Pod’s container.

Adjusting the Cluster Configuration

Update the cluster configuration:

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$ kubectl apply -f yml文件路径

Delete a deployment or service:

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# Delete Deployment
$ kubectl delete deployment 部署名称
# Delete Service
$ kubectl delete service 服务名称

Setting Cluster Resource Limits

We mainly add the resources configuration option to the container configuration to set resource limits.

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containers:
  - name: tomcat-cluster
  image: tomcat:latest
  resources:
    requests:        # Minimum resource required to run the container, if not satisfied, cannot run
      cpu: 1         # One nuclear cpu can be decimal, for example 0.5, which means that this container can be deployed as long as the host is 0.5 nuclear cpu is idle.
      memory: 500Mi  # 500M RAM
    limits:          # Most occupied resources during container operation
      cpu: 2         # Up to 2 corecpu
      memory: 1024Mi # Up to 1G RAM

Testing Resource Adjustments and Deployment

We modify the tomcat-deploy.yml file on the server, add resource limits, and increase the number of replicas to 3.

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apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: tomcat-deploy
spec: 
  replicas: 3 #Number of copies changed from 2 to 3
  template:
    metadata:
      labels:
        app: tomcat-cluster
    spec:
      volumes: 
      - name: web-app
        hostPath:
          path: /mnt
      containers:
      - name: tomcat-cluster
        image: tomcat:latest
        resources: # Additional resource limitations
          requests:
            cpu: 0.5
            memory: 200Mi
          limits:
            cpu: 2
            memory: 500Mi
        ports:
        - containerPort: 8080
        volumeMounts:
        - name: web-app
          mountPath: /usr/local/tomcat/webapps

Update the cluster configuration:

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kubectl apply -f tomcat-deploy.yml

Check the cluster’s Pod information. The number of Pods has increased to 3.

It is worth noting that K8S follows a “resources first” principle when deploying Pods. In other words, a Pod is preferentially deployed to the node with more available resources.

Check whether the configuration has taken effect using the command kubectl describe pod tomcat-deploy-857545df88-26v5t.

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[root@master tomcat-deploy]# kubectl describe pod tomcat-deploy-857545df88-26v5t
Name:               tomcat-deploy-857545df88-26v5t
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               node2/192.168.233.130
Start Time:         Fri, 15 Jan 2021 18:50:38 +0800
Labels:             app=tomcat-cluster
                    pod-template-hash=857545df88
Annotations:        <none>
Status:             Running
IP:                 10.244.2.11
Controlled By:      ReplicaSet/tomcat-deploy-857545df88
Containers:
  tomcat-cluster:
    Container ID:   docker://8f769d695c7f1713027a043a8e11edcf1ad3cb55ae731ca925c0573482174792
    Image:          tomcat:latest
    Image ID:       docker-pullable://tomcat@sha256:94cc18203335e400dbafcd0633f33c53663b1c1012a13bcad58cced9cd9d1305
    Port:           8080/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Fri, 15 Jan 2021 18:50:43 +0800
    Ready:          True
    Restart Count:  0
    Limits:         # Resource constraints are in effect
      cpu:     2
      memory:  500Mi    
    Requests:
      cpu:        500m
      memory:     200Mi
    Environment:  <none>
    Mounts:
      /usr/local/tomcat/webapps from web-app (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-fkln2 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  web-app:
    Type:          HostPath (bare host directory volume)
    Path:          /mnt
    HostPathType:  
  default-token-fkln2:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-fkln2
    Optional:    false
QoS Class:       Burstable
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age    From               Message
  ----    ------     ----   ----               -------
  Normal  Scheduled  8m36s  default-scheduler  Successfully assigned default/tomcat-deploy-857545df88-26v5t to node2
  Normal  Pulling    8m35s  kubelet, node2     Pulling image "tomcat:latest"
  Normal  Pulled     8m31s  kubelet, node2     Successfully pulled image "tomcat:latest"
  Normal  Created    8m31s  kubelet, node2     Created container tomcat-cluster
  Normal  Started    8m31s  kubelet, node2     Started container tomcat-cluster