Spring Boot is a popular Java-based framework used for developing microservices. In this post, we'll learn how to containerize a Spring Boot application and deploy it to Kubernetes and Docker Swarm.
To containerize a Spring Boot application, we'll first need to create a Dockerfile. A Dockerfile is a text file that contains instructions for building a Docker image.
We'll start by creating a Dockerfile in the root directory of our Spring Boot project.
FROM openjdk:8-jdk-alpine
VOLUME /tmp
ARG JAR_FILE
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]
In this Dockerfile, we're using openjdk:8-jdk-alpine as our base image. We're also using a VOLUME to create a mount point for storing temporary files.
Next, we'll copy our Spring Boot .jar file into the container as app.jar and set it as the ENTRYPOINT.
Now that we have our Dockerfile, we can build our Docker image. We'll use the docker build command to build our image, tagging it with the latest tag.
$ docker build -t my-spring-boot-app:latest .
Kubernetes is a popular container orchestration platform. It can be used to manage a group of containers as a single unit.
To deploy our Spring Boot application to Kubernetes, we'll first need to create a Deployment. A Deployment defines a group of identical pods and ensures that a certain number of them are always running.
We'll create a deployment.yaml file in the root directory of our project.
apiVersion: apps/v1
kind: Deployment
metadata:
name: my-spring-boot-app
labels:
app: my-spring-boot-app
spec:
replicas: 3
selector:
matchLabels:
app: my-spring-boot-app
template:
metadata:
labels:
app: my-spring-boot-app
spec:
containers:
- name: my-spring-boot-app
image: my-spring-boot-app:latest
ports:
- containerPort: 8080
In this file, we've defined a Deployment with a replica count of 3. We've also defined a selector and template which specify the pods that the Deployment will manage.
Now, we can create our Deployment in Kubernetes using the kubectl command-line tool.
$ kubectl apply -f deployment.yaml
Docker Swarm is a container orchestration platform from Docker. It can be used to manage a group of Docker containers as a single unit.
To deploy our Spring Boot application to Docker Swarm, we'll first need to create a Stack. A Stack is a group of services that are deployed together.
We'll create a stack.yaml file in the root directory of our project.
version: "3.1"
services:
my-spring-boot-app:
image: my-spring-boot-app:latest
ports:
- "8080:8080"
deploy:
replicas: 3
In this file, we've defined a Stack with a single service, my-spring-boot-app. We've also specified that we want 3 replicas of this service to be deployed.
Now, we can deploy our Stack to Docker Swarm using the docker stack command.
$ docker stack deploy -c stack.yaml my-spring-boot-app
Service to expose your application to the outside world.Network to allow communication between your services.