In the previous article, we introduced how to deploy a Tomcat cluster using the Dashboard’s graphical interface. However, in an actual cluster environment, we usually deploy the cluster by writing Deployment scripts.

Deployment

• Deployment refers to the process in which Kubernetes sends instructions to Node nodes to create containers.

• Kubernetes supports deployment scripts in yml format.

• The deployment command is as follows:

1

kubectl create -f [部署yml脚本文件]  # Create Deployment

Basic Deployment Script Format

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16

apiVersion: extensions/v1beta1  # Api's version number
kind: Deployment                # The "type" of the current script indicates deployment; Service means service; Pod means Pod script
metadata:                       # Metadata, mainly used to configure basic information on currently deployed scripts
  name: tomcat-deploy           # Name of current deployment
spec:                           # Detailed definition information
  replicas: 2                   # Number of copies deployed, that's a few pops.
  template:                     # Deployment template information
    metadata:                   # Deployment of metadata for templates
      labels:                   # Pod tag
        app: tomcat-cluster     # Custom labels are specified here
    spec:                       # Details of the template
      containers:               # Container information
      - name: tomcat-cluster    # Name of container
        image: tomcat:latest    # Mirror of the container. Here's the latest version of Tomcat.
        ports:
        - containerPort: 8080   # Port for external exposure of containers

Common kubectl Commands Related to Deployment

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20

# Create Deployment
kubectl create -f 部署yml文件

# Update deployment configuration, if first deployed, this command is equivalent to kubectl profile
kubectl apply -f 部署yml文件

# View deployed pop
kubectl get pod [-o wide]

# View Pod Details
kubectl describe pod pod名称

# See if pop output log -f is updated in real time
kubectl logs [-f] pod名称

# View created deployments
kubectl get deployment

# Delete a deployment
kubectl delete deployment 部署名称

Manually Deploying a Tomcat Cluster

Here, we store all deployment scripts in the /usr/local/k8s/tomcat-deploy directory. You can also create your own directory for storing deployment scripts.

• Create the directory

  1 2	$ mkdir /usr/local/k8s/tomcat-deploy $ cd /usr/local/k8s/tomcat-deploy

• Write the deployment script

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

  $ vim tomcat-deployment.yml # Enter the following content apiVersion: extensions/v1beta1 kind: Deployment metadata: name: tomcat-deploy spec: replicas: 2 template: metadata: labels: app: tomcat-cluster spec: containers: - name: tomcat-cluster image: tomcat:latest ports: - containerPort: 8080

  

• Deploy the Tomcat cluster

  1 2	$ kubectl create -f tomcat-deploy.yml deployment.extensions/tomcat-deploy created

• View the deployed pods

  1 2 3 4

  [root@master tomcat-deploy]# kubectl get pods NAME READY STATUS RESTARTS AGE tomcat-deploy-5fd4fc7ddb-7vw4f 1/1 Running 0 98s tomcat-deploy-5fd4fc7ddb-t4wvp 1/1 Running 0 98s

  We can see that two pod have been started, and both are in the Running state. These two pod are deployed on node1 and node2, respectively.

• At this point, the Tomcat cluster has been deployed. We can use the kubectl describe pod [pod-name] command to view detailed information about the pod deployment.

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

  $ kubectl describe pod tomcat-deploy-5fd4fc7ddb-7vw4f Name: tomcat-deploy-5fd4fc7ddb-7vw4f Namespace: default Priority: 0 PriorityClassName: <none> Node: node1/192.168.233.129 Start Time: Fri, 15 Jan 2021 11:43:22 +0800 Labels: app=tomcat-cluster pod-template-hash=5fd4fc7ddb Annotations: <none> Status: Running IP: 10.244.1.7 Controlled By: ReplicaSet/tomcat-deploy-5fd4fc7ddb Containers: tomcat-cluster: Container ID: docker://fa36632bdf28f58e1ad61dee3c93da88df348d3a98c34531d4b6fa12a73a18f8 Image: tomcat:latest Image ID: docker-pullable://tomcat@sha256:94cc18203335e400dbafcd0633f33c53663b1c1012a13bcad58cced9cd9d1305 Port: 8080/TCP Host Port: 0/TCP State: Running Started: Fri, 15 Jan 2021 11:43:38 +0800 Ready: True Restart Count: 0 Environment: <none> Mounts: /var/run/secrets/kubernetes.io/serviceaccount from default-token-fkln2 (ro) Conditions: Type Status Initialized True Ready True ContainersReady True PodScheduled True Volumes: default-token-fkln2: Type: Secret (a volume populated by a Secret) SecretName: default-token-fkln2 Optional: false QoS Class: BestEffort 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 4m1s default-scheduler Successfully assigned default/tomcat-deploy-5fd4fc7ddb-7vw4f to node1 Normal Pulling 4m kubelet, node1 Pulling image "tomcat:latest" Normal Pulled 3m45s kubelet, node1 Successfully pulled image "tomcat:latest" Normal Created 3m45s kubelet, node1 Created container tomcat-cluster Normal Started 3m45s kubelet, node1 Started container tomcat-cluster

Accessing the Tomcat Cluster Externally Using NodePort

We deployed an tomcat cluster above, but this cluster can only be accessed from within the cluster. How can we expose tomcat for external access? Looking back at our Deployment deployment script, we can see the following two lines:

1
2
3

# Tomcat-deploy.yml files
ports:
        - containerPort: 8080

We only set the container’s exposed port to 8080, without configuring any settings for external access.

As shown below, we can deploy a Service. This Service is also a pod and has its own virtual IP address and port. The service pod is deployed on the master node. When an external request arrives, it is first sent to port 8000 of the service and then distributed to the two Tomcat containers according to the load-balancing rules. The service here can be understood as a load balancer on the K8S cluster.

Creating a Tomcat Service

• Create the script

  Similar to deploying Deployment, we create a service script file in the /usr/local/k8s/tomcat-service/ directory.

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

  $ cd /usr/local/k8s/tomcat-service $ vim tomcat-service.yml apiVersion: v1 # Version kind: Service # Deployment type: Service metadata: # Metadata name: tomcat-service # The service name is tomcat-service labels: # Pod labels (because a service is also a pod) app: tomcat-service # Custom label name: tomcat-service spec: # Detailed configuration type: NodePort # Set the service type to NodePort, meaning that a port will be opened and mapped to the Tomcat container selector: # Selector used to select the pods to which this service will bind by label app: tomcat-cluster # Select pods with the tomcat-cluster label, namely the Tomcat pods deployed in the previous step ports: # Port configuration - port: 8000 # Port on which the current service receives data targetPort: 8080 # Target port, which points to the port of the child Tomcat containers nodePort: 32500 # Port exposed externally by the child Tomcat containers (directly accessible from outside)

• Deploy the service

  1 2	$ kubectl create -f tomcat-service.yml service/tomcat-service created

  This message indicates that the service has been created.

• View the service details

  1 2 3 4

  $ kubectl get service NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 18h tomcat-service NodePort 10.107.253.196 <none> 8000:32500/TCP /+++++ 2m3s