Deploy a Java Application on Kubernetes: From Image Build to Service Exposure

Kubernetes Basic Concepts

Pod :

1. Smallest deployment unit,
2. A group of containers,
3. Containers in a pod share network namespace,
4. Lifecycle is short‑lived,

Controllers :

1. Deployment: deploy stateless apps
2. StatefulSet: deploy stateful apps
3. ReplicaSet: ensure desired pod replica count
4. DaemonSet: ensure a pod runs on each node
5. Job: one‑time tasks
6. CronJob: scheduled tasks
Higher‑level objects for deploying and managing pods

Service :

Prevents pod isolation, finds required pod
Defines load‑balancing access policy for a set of pods

Label :

Tag attached to a resource for association, query, and filtering

Namespaces :

Logical or resource isolation for objects

Project Migration to Kubernetes Process

Base image → runtime image (Python/PHP/Go/Java) → project image (packaged project)

Practical Project Steps

1. Import Java source package to the master server

192.168.106.102 – k8s-master

192.168.106.103 – k8s-node01

192.168.106.104 – k8s-node02

192.168.106.103 – MySQL database

2. Import database files into MySQL (node01)

# Execute on 192.168.106.103
source /root/tables_ly_tomcat.sql
granted all on test.* to 'test'@'%' identified by "Zhangfan@123";

Modify the application configuration to use the new database user and IP.

vim src/main/resources/application.yml

3. Build the Java Docker image on the master

cat Dockerfile
FROM centos:7
MAINTAINER zhangfan
ENV VERSION=8.5.61
RUN yum install -y java-1.8.0-openjdk wget curl unzip iproute net-tools && yum clean all && rm -rf /var/cache/yum/*
RUN wget https://mirrors.tuna.tsinghua.edu.cn/apache/tomcat/tomcat-8/v${VERSION}/bin/apache-tomcat-${VERSION}.tar.gz && \
    tar zxf apache-tomcat-${VERSION}.tar.gz && \
    mv apache-tomcat-${VERSION} /usr/local/tomcat && \
    rm -rf apache-tomcat-${VERSION}.tar.gz && \
    rm -rf /usr/local/tomcat/webapps/* && \
    mkdir /usr/local/tomcat/webapps/test && \
    echo "ok" > /usr/local/tomcat/webapps/test/status.html && \
    sed -i '1a JAVA_OPTS="-Djava.security.egd=file:/dev/./urandom"' /usr/local/tomcat/bin/catalina.sh && \
    ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
ENV PATH $PATH:/usr/local/tomcat/bin
WORKDIR /usr/local/tomcat
EXPOSE 8080
CMD ["catalina.sh", "run"]

4. Install build tools and compile the project

yum -y install java-1.8.0-openjdk maven
cd /root/tomcat-java-demo-master
mvn clean package -Dmaven.test.skip=true

The build produces a WAR file.

5. Create a new Dockerfile for the project image

cat Dockerfile
FROM tomcat:v1
LABEL test www.zhangsan.com
RUN rm -rf /usr/local/tomcat/webapps/*
ADD target/*.war /usr/local/tomcat/webapps/ROOT.war
# Build and tag the image
docker build -t zhangfan5391621/java-demo .

6. Push the image to Docker Hub

docker push zhangfan5391621/java-demo   # Upload to Docker Hub

7. Generate a Kubernetes Deployment YAML

kubectl create deployment java-demo --image=zhangfan5391621/java-demo --dry-run -o yaml > deploy.yaml

Sample deploy.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: java-demo
  name: java-demo
spec:
  replicas: 3
  selector:
    matchLabels:
      app: java-demo
  template:
    metadata:
      labels:
        app: java-demo
    spec:
      containers:
      - image: zhangfan5391621/java-demo
        name: java-demo

kubectl apply -f deploy.yaml   # Create the pods
kubectl get pods               # Verify all pods are Running

8. Expose the application via a Service

kubectl expose deployment java-demo --port=80 --target-port=8080 --type=NodePort -o yaml --dry-run > svc.yaml
kubectl apply -f svc.yaml
kubectl get pods,svc

Access the service at http://<master-ip>:<NodePort> (e.g., http://192.168.106.102:30187/).

The complete deployment order is: build environment image → build project image → push to Docker Hub → create Deployment → expose Service.