Deploy sample Java application in Kubernetes

Introduction

Apache tomcat also known as Tomcat, is an open-source web server and servlet container developed by the Apache Software Foundation. It is used to deploy and run Java-based web applications. Tomcat implements the Java Servlet and the JavaServer Pages (JSP) specifications from Oracle Corporation and provides a “pure Java” HTTP web server environment for Java code to run in.

Kubernetes is a powerful Platform as a Service that enables you to manage a cluster of nodes that run the Linux operating system. Kubernetes can be used to manage a variety of applications, including web applications, database and more.

Details about the Kubernetes components

• API Server – Intract with kubectl command utility, Primary component, Authorization work.
• Controller Manager – Replica controller, Node Controller maintainer the define pods and nodes.
• Scheduler – Matain proper balacing of hardware utilization and assign new pods to sutable workder node as per ranking.
• ECTD – Database its store the data using key and value form format.
• Kubelet – Pod moniotr, Pod creation and deletation.
• Kube-proxy – Pods communication between 2 nodes, Network related rules manages by kube-proxy.

In this post, We will deploy the JAVA app on Kubernetes cluster.

Step 1: Write a Deployment YAML

To deploy the tomcat docker container in K8s, you can use the provided code by creating a deployment YAML file with the name tomcat-deployment.yaml.

vim tomcat-deployment.yaml

and paste the following code.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: tomcat
  labels:
    app: tomcat
spec:
  replicas: 1
  selector:
    matchLabels:
      app: tomcat
  template:
    metadata:
      labels:
        app: tomcat
    spec:
      containers:
      - name: tomcat
        image: openjdk:8-jre
        ports:
        - containerPort: 8080

Take a look at the above YaML configuration:

apiVersion: Define the Kubernetes API in order to create objects.
kind: specify the type of object you intend to create.
metadata: define the object name ( including a name string, uniquely identifying the object, the UID, and an optional namespace ).
spec: Define the state of objects.
selector: specify the mapping between deployment and managed pods. 

We need to save and exit from text editor, Our deployment YAML is ready Lets deploy the apache pod on K8s cluster.

Step 2: Create a Deployment

We need to execute the following command to deploy the nginx pods which is container nginx image.

kubectl create -f tomcat-deployment.yaml

You will get success message for the tomcat deployment on your screen.

We will get a single pod of the tomcat/opennJDK image and, according to the Dockerfile configuration, tomcat will be up and running on port 8080. 

Step 3: Let’s Verify the Deployment

We need to execute the given command to see pods and running or not.

To Validate the pod.

kubectl get pods

To check deployment.

kubectl get deployment

Step 4: Create a Service

We need to create a tomcat-service.yaml file in order access tomcat server, Create a tomcat-service.yaml file with following code.

To create a service.yaml file

vim tomcat-service.yaml

Paste the following code.

apiVersion: v1
kind: Service
metadata:
  name: tomcat-service
spec:
  selector:
    app: tomcat
  type: NodePort
  ports:
  - protocol: TCP
    port: 8080
    targetPort: 8080

The Kubernetes service section: K8s services allow network access to the set of pods.

port: Define the application’s port inside the Docker container.
nodePort: The port number to use to connect to the base machine.
protocol: define a network layer type like TCP/UDP. To communicate with the network.
selector: To know and identify the deployment-created objects.

Save and close the text editor. As per our service configuration, we define port 8080 to access the tomcat app, which is mapped with a label like app: tomcat, We are using NodePort to access the tomcat app server on each node using port 8080.

Step 5: Deploy Service

We need to execute the given command to deploy the tomcat-service on K8s cluster.

kubectl create -f tomcat-service.yaml

We should get a success message on the screen, To check the service status for tomcat, execute the given command.

To get service status.

kubectl get svc 

Here we can see that NodePort assigned the ramdon port to access the tomcat app on each node

Note: If you are using minikube So you need to use the given command to expose the total url to access your kubernets application.

minikube service tomcat-service --url

Click here to get apache deployment process step by step on kubernetes cluster.

Conclusion

We have successfully deploy JAVA app on kubernetes cluster in a simple way, If you still have questions, please post them in the comments section below.