Execute multi-container applications (Spring boot & PostgreSQL)

  • Use Case
    • Run a dockerized spring boot application which has dependency on PostgreSQL docker container
    • Initialize the database with data while its getting created
    • Mount an external volume so that the data does not get lost when container exits
  • Solution:
  • Step 1: Build a micro service using spring boot to be containerized
    • Clone the following spring boot implementation
    • The example service contains one end point to return all customer details
    • Service uses Spring JPA and PostgreSQL database
    • Snippet of application.properties file
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect

  • Step 2: Dockerize the micro service
    • Build the application to generate jar file
      • mvn clean install -DskipTests
    • Create a dockerfile and add the below content (Already available in the git repo)
FROM openjdk:8-jdk-alpine
RUN mkdir -p /app/
RUN mkdir -p /app/logs/
ADD target/order-0.0.1-SNAPSHOT.jar /app/app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-Dspring.profiles.active=container", "-jar", "/app/app.jar"]
  • Dockerfile has mainly instructions to add openjdk 8 image, expose port 8080 and add the generated jar file from previous step to the image
  • To build an image with the name order-svc from the Dockerfile , run the below command
    • docker build -t order-svc .
  • To view the images run docker images
  • Step 3: Define the Docker Compose yml file
    • Now we have a docker image , which has a dependency on PostgreSQL database
    • Next step is to define a docker-compose.yml file which will have a configuration to create a PostgreSQL database in a Docker container and connect it to the order-svc container of spring boot project to run as a multi-container application.
    • Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.
    • Using Compose is basically a three-step process:
      1. Define your app’s environment with a Dockerfile .
      2. Define the services that make up your app in docker-compose.yml so they can be run together in an isolated environment.
      3. Run docker compose up and the Docker compose command starts and runs your entire app.
    • In the project directory, create a docker-compose.yml file. It is available in the projects root directory in git .
  • The above configurations define the services in the multi-container application.
  • Now, you can run your multi-container application with Docker Compose.
  • Step 4: Run the application
    • Execute docker compose up
    • It will fire the application
  • Test the application with curl http://localhost:8080/api/v1/customers

Thank you . Please share your comments / feedback

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