How do you configure environment variables in a Dockerized Spring Boot application?

Table of Contents

• Introduction
• Methods to Configure Environment Variables in Dockerized Spring Boot
  • 1. Use Docker -e Flag to Set Environment Variables
    • Example: Setting Environment Variables
  • 2. Pass Environment Variables through a Docker Compose File
    • Example: Docker Compose Configuration
  • 3. Use .env File for Environment Variables
    • Example: .env File
  • 4. Access Environment Variables in Spring Boot
    • Example: application.properties
  • 5. Using Dockerfile to Set Default Environment Variables (Optional)
    • Example: Dockerfile with ENV
• Conclusion

Introduction

Configuring environment variables in a Dockerized Spring Boot application allows you to manage dynamic settings and configurations, such as database credentials, API keys, or application-specific properties. Environment variables offer flexibility, especially when deploying the application across different environments (development, testing, production) or when configuring the app in a cloud-based or containerized setup like Docker.

In this guide, we'll show you how to configure environment variables in a Spring Boot application running inside a Docker container, enabling dynamic and environment-specific configurations.

Methods to Configure Environment Variables in Dockerized Spring Boot

1. Use Docker -e Flag to Set Environment Variables

The simplest way to configure environment variables for your Spring Boot application inside Docker is by using the -e flag when running the Docker container. This flag allows you to define environment variables directly in the docker run command.

Example: Setting Environment Variables

Explanation:

• -e SPRING_DATASOURCE_URL=jdbc:mysql://localhost:3306/mydb: Sets the SPRING_DATASOURCE_URL environment variable for the Spring Boot application.
• -e SPRING_DATASOURCE_USERNAME=root: Sets the SPRING_DATASOURCE_USERNAME variable.
• -e SPRING_DATASOURCE_PASSWORD=rootpassword: Sets the SPRING_DATASOURCE_PASSWORD variable.
• spring-boot-app: Specifies the name of the Docker image.

Spring Boot automatically maps environment variables like SPRING_DATASOURCE_URL, SPRING_DATASOURCE_USERNAME, and SPRING_DATASOURCE_PASSWORD to its internal configuration properties.

2. Pass Environment Variables through a Docker Compose File

If you're using Docker Compose to manage multi-container environments, you can pass environment variables using the environment directive in the docker-compose.yml file.

Example: Docker Compose Configuration

In this configuration:

• The environment section in the spring-boot-app service defines environment variables.
• SPRING_DATASOURCE_URL, SPRING_DATASOURCE_USERNAME*, and SPRING_DATASOURCE_PASSWORD are passed to the Spring Boot application.
• The MySQL service is also configured with the required root password and database name.

Run the application with:

This command starts both the Spring Boot application and MySQL container, passing environment variables to the Spring Boot app at runtime.

3. Use .env File for Environment Variables

Docker Compose supports loading environment variables from a .env file, which can be useful for organizing environment-specific configurations. You can store variables in a .env file and reference them in the docker-compose.yml file.

Example: .env File

Create a .env file in the same directory as your docker-compose.yml:

Then reference these variables in the docker-compose.yml file:

Docker Compose will automatically load the variables from the .env file when you run docker-compose up.

4. Access Environment Variables in Spring Boot

Spring Boot has built-in support for environment variables, and you can access them directly in your application configuration.

Example: application.properties

Spring Boot will automatically bind environment variables to properties in your application.properties or application.yml file.

Here, SPRING_DATASOURCE_URL, SPRING_DATASOURCE_USERNAME, and SPRING_DATASOURCE_PASSWORD will be replaced by the environment variables set either in the docker run command or in the docker-compose.yml file.

5. Using Dockerfile to Set Default Environment Variables (Optional)

You can also set default environment variables in the Dockerfile for your Spring Boot application. However, these variables can be overridden by values passed during container runtime.

Example: Dockerfile with ENV

In this example, the default values for SPRING_DATASOURCE_URL, SPRING_DATASOURCE_USERNAME, and SPRING_DATASOURCE_PASSWORD are set. These defaults can still be overridden when running the container using the docker run -e flag or via a docker-compose.yml file.

Conclusion

Configuring environment variables for a Dockerized Spring Boot application provides flexibility in managing dynamic configurations across different environments. You can set environment variables at runtime using the docker run -e flag, manage them in a docker-compose.yml file, or use a .env file for easier configuration management. Additionally, Spring Boot natively supports environment variable injection, allowing you to access these values seamlessly in your application’s configuration.

By properly managing environment variables, you can ensure your Spring Boot application behaves consistently and securely across various deployment environments. Whether you're working locally or in production, Docker makes it easy to configure and manage your application's settings.