Externalising Spring Boot properties when deploying to Docker

I personally would consider two options:

1. Using an environment variable per config

   app:
     image: my-app:latest
     ports:
       - "8080:8080"
     environment:
        SPRING_DATASOURCE_URL=jdbc:mysql://db:3306/table
   

2. Using SPRING_APPLICATION_JSON

   app:
     image: my-app:latest
     ports:
       - "8080:8080"
     environment:
       SPRING_APPLICATION_JSON: '{
         "spring.datasource.url": "jdbc:mysql://db:3306/table",
       }'
   

DOCKER IMAGE CONFIGURATION

If you look to the way Spring recommends to launch a Spring Boot powered docker container, that's what you find:

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"]

That means your image extends openjdk and your container has its own environment. If you're doing like that, it would be enough to declare what you want to override as environment properties and Spring Boot will fetch them, since environment variables take precedence over the yml files.

Environment variables can be passed in your docker command too, to launch the container with your desired configuration. If you want to set some limit for the JVM memory, see the link below.

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DOCKER COMPOSE SAMPLE

Here you have an example of how I launch a simple app environment with docker compose. As you see, I declare the spring.datasource.url property here as an environment variable, so it overrides whatever you've got in your application.yml file.

version: '2'
services:
    myapp:
        image: mycompany/myapp:1.0.0
        container_name: myapp
        depends_on:
        - mysql
        environment:
            - SPRING_DATASOURCE_URL=jdbc:mysql://mysql:3306/myapp?useUnicode=true&characterEncoding=utf8&useSSL=false
        ports:
            - 8080:8080

    mysql:
        image: mysql:5.7.19
        container_name: mysql
        volumes:
            - /home/docker/volumes/myapp/mysql/:/var/lib/mysql/
        environment:
            - MYSQL_USER=root
            - MYSQL_ALLOW_EMPTY_PASSWORD=yes
            - MYSQL_DATABASE=myapp
        command: mysqld --lower_case_table_names=1 --skip-ssl --character_set_server=utf8

See also:

• How do I pass environment variables to Docker containers?
• Limit JVM memory consumption in a Docker container