How to Connect a Spring Boot Application to a Docker Image

What steps should I follow to connect my Spring Boot application to a Docker image?

@SpringBootApplication
public class MySpringBootApplication {
    public static void main(String[] args) {
        SpringApplication.run(MySpringBootApplication.class, args);
    }
}

Connecting a Spring Boot application to a Docker image involves understanding how to configure the application properties, utilize Docker networking, and ensure correct service binding and connection settings.

# Dockerfile example for a Spring Boot app
FROM openjdk:17-jdk-slim
VOLUME /tmp
COPY target/myapp-0.0.1-SNAPSHOT.jar app.jar
ENTRYPOINT ["java","-jar","/app.jar"]
EXPOSE 8080

Causes

• Misconfigured Docker networking settings.
• Incorrect application properties in the Spring Boot configuration.
• Issues with container ports not being exposed correctly.
• Not using the correct IP address or hostname for the Docker container.

Solutions

• Ensure the Docker container is running and accessible.
• Check the application.properties for database connectivity and adjust for Docker's internal networking.
• Use Docker Compose for easy management of multiple containers.
• Expose the right ports in the Dockerfile using the EXPOSE command.

Mistake: Forgetting to expose the correct port in the Dockerfile.

Solution: Add EXPOSE 8080 to your Dockerfile to allow connections.

Mistake: Using localhost instead of container name to connect the database.

Solution: Use the service name defined in Docker Compose instead of localhost.

Mistake: Ignoring Docker network restrictions, leading to connection timeouts.

Solution: Verify that all containers are on the same Docker network and can communicate.