How to implement Docker to dynamically pass parameters to Springboot projects

background

Recently, some friends who are new to Docker asked me that they want to dynamically pass parameters to microservices through docker-compose.yml , instead of hard-coding them in the project configuration file every time, then building the service image, and finally packaging and publishing it through a series of processes to update the configuration. So, is it possible to directly put some configuration items into environment variables in docker-compose.yml , and then the springboot project automatically obtains parameters from the environment variables?

Scenario

Suppose there is a Springboot project with a database configuration item in it, but there are multiple database IPs in different database test environments (DEV\SIT\UAT). If you want to use the same Springboot project image, you can switch the database configuration at any time. In short, the database configuration of your Springboot application should be passed in externally instead of hardcoded.

There is a database configuration in the Springboot application as follows:

spring.datasource.url = jdbc:mysql://192.168.0.11:3306/db?useUnicode=true&characterEncoding=utf8
#Configure database username spring.datasource.username = sa
#Configure database password spring.datasource.password = sa

Solution

Use SpEL expressions to dynamically obtain database configuration from environment variables

Next, we replace the database configuration with a spEL expression in the Springboot configuration file

#Configure database link spring.datasource.url = jdbc:mysql://${DB_HOST}:${DB_PORT}/${DB_NAME}?useUnicode=true&characterEncoding=utf8
#Configure database username spring.datasource.username = ${DB_USER}
#Configure database password spring.datasource.password = ${DB_PASSWORD}

Configure our database parameters in docker-compose.yml

version: '3'
services:
 web:
  restart: always
  depends_on:
   -db
  image: springboot-app-image
  build: .
  ports:
   - 8080:8080
  environment:
   - DB_HOST=192.168.0.11
   - DB_PORT=3306
   - DB_USER=root
   - DB_PASSWORD=123456
   - DB_NAME=db
  networks:
   - credit-facility-net
  deploy:
   mode: replicated
   replicas: 3
   restart_policy:
    condition: on-failure
    delay: 5s
    max_attempts: 3
   update_config:
    parallelism: 1
    delay: 10s

In this way, our Springboot application can dynamically obtain the database configuration when starting the container service

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