Deploying a Spring Boot application involves moving your application from a development environment to a production environment where it can be accessed by users. This process can vary depending on the target environment, such as cloud platforms, on-premises servers, or container orchestration systems like Kubernetes. In this section, we will cover the fundamental concepts and steps involved in deploying a Spring Boot application.

1. Build and Package: Before deployment, your Spring Boot application needs to be built and packaged into a deployable format, typically a JAR (Java ARchive) or WAR (Web Application ARchive) file.
2. Environment Configuration: Different environments (development, staging, production) may require different configurations. Spring Boot supports externalized configuration to handle this.
3. Deployment Targets: Common deployment targets include cloud platforms (e.g., Heroku, AWS), container platforms (e.g., Docker, Kubernetes), and traditional servers.
4. Continuous Integration/Continuous Deployment (CI/CD): Automating the build, test, and deployment process using CI/CD pipelines can streamline and improve the reliability of deployments.

First, you need to build and package your Spring Boot application. This can be done using Maven or Gradle.

Using Maven:

Using Gradle:

This will generate a JAR file (or WAR file if your application is configured as a web application) in the target (or build/libs) directory.

Spring Boot allows you to externalize your configuration so that you can use different settings for different environments. This can be done using properties files, YAML files, environment variables, or command-line arguments.

Example: application.properties for development:

Example: application-prod.properties for production:

You can specify which profile to use by setting the spring.profiles.active property.

Example:

Deploying to Heroku

1. Install the Heroku CLI: Follow the instructions on the Heroku website to install the Heroku CLI.
2. Create a Heroku App:

   heroku create my-spring-boot-app
   

3. Deploy the Application:

   git push heroku main
   

Deploying to AWS

1. Create an AWS Elastic Beanstalk Environment: Follow the instructions on the AWS Elastic Beanstalk documentation.
2. Deploy the Application: Use the AWS Management Console or the AWS CLI to upload your JAR/WAR file and deploy it to the Elastic Beanstalk environment.

Deploying to Kubernetes

1. Create a Docker Image:

   FROM openjdk:11-jre-slim
   COPY target/myapp.jar /app.jar
   ENTRYPOINT ["java", "-jar", "/app.jar"]
   

   Build the Docker image:

   docker build -t myapp:latest .
   

2. Deploy to Kubernetes: Create a Kubernetes deployment and service configuration.

   apiVersion: apps/v1
   kind: Deployment
   metadata:
     name: myapp-deployment
   spec:
     replicas: 3
     selector:
       matchLabels:
         app: myapp
     template:
       metadata:
         labels:
           app: myapp
       spec:
         containers:
         - name: myapp
           image: myapp:latest
           ports:
           - containerPort: 8080
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: myapp-service
   spec:
     type: LoadBalancer
     selector:
       app: myapp
     ports:
     - protocol: TCP
       port: 80
       targetPort: 8080
   

   Apply the configuration:

   kubectl apply -f myapp-deployment.yaml
   

In this section, we covered the fundamental concepts and steps involved in deploying a Spring Boot application. We discussed the importance of building and packaging the application, configuring it for different environments, and choosing a deployment target. We also provided examples of deploying to Heroku, AWS, and Kubernetes. Understanding these concepts and steps will prepare you for deploying your Spring Boot applications in various environments.