Environment Variables

Environment variables store configuration values outside your code. They're the standard way to handle secrets and environment-specific settings.

Why Environment Variables?

# BAD: Secrets in code (NEVER do this)
spring:
  datasource:
    password: mySecretPassword123  # Committed to Git!

# GOOD: Secrets in environment variables
spring:
  datasource:
    password: ${DB_PASSWORD}  # Value set at deployment time

Setting Environment Variables

# Linux/Mac
export DB_PASSWORD=mySecretPassword123
export JWT_SECRET=myJwtSecretKey456
java -jar app.jar

# Windows CMD
set DB_PASSWORD=mySecretPassword123
java -jar app.jar

# Windows PowerShell
$env:DB_PASSWORD="mySecretPassword123"
java -jar app.jar

# Docker
docker run -e DB_PASSWORD=mySecretPassword123 myapp

# Kubernetes (Secret)
kubectl create secret generic db-secret --from-literal=password=mySecretPassword123

Accessing in Spring Boot

# application.yml — reference env vars with defaults
spring:
  datasource:
    url: jdbc:postgresql://${DB_HOST:localhost}:${DB_PORT:5432}/${DB_NAME:mydb}
    username: ${DB_USERNAME:postgres}
    password: ${DB_PASSWORD:}

app:
  jwt:
    secret: ${JWT_SECRET:}
    expiration: ${JWT_EXPIRATION:86400000}

Standard Environment Variables

Variable	Purpose
DB_HOST	Database hostname
DB_PORT	Database port
DB_NAME	Database name
DB_USERNAME	Database username
DB_PASSWORD	Database password (SECRET)
JWT_SECRET	JWT signing key (SECRET)
API_KEY	External API key (SECRET)
LOG_LEVEL	Logging level
SPRING_PROFILES_ACTIVE	Active profile

Security Rules

1. Never commit secrets to Git — use .gitignore
2. Never log secrets — mask them in application.yml
3. Rotate secrets regularly — change passwords periodically
4. Use secrets managers — AWS Secrets Manager, HashiCorp Vault
5. Least privilege — database user with minimal permissions

Spring Boot .env File (Development Only)

# .env (NEVER commit to Git)
DB_PASSWORD=localdevpassword
JWT_SECRET=dev-only-secret-key

<!-- pom.xml — use dotenv for local dev -->
<dependency>
    <groupId>me.paulschwarz</groupId>
    <artifactId>spring-dotenv</artifactId>
    <version>4.0.0</version>
</dependency>

Key Principles

1. Follow SOLID principles
2. Write clean, readable code
3. Test thoroughly
4. Document decisions
5. Monitor in production

Implementation

• Start simple, refactor as needed
• Use established patterns
• Consider trade-offs
• Review with peers

Continuous Improvement

• Learn from incidents
• Update documentation
• Share knowledge
• Mentor others

Key Points

• Understanding Environment Variables is essential for production systems
• Always consider scalability and maintainability
• Test thoroughly before deploying to production
• Monitor performance and set up alerting

Common Patterns

1. Validation: Always validate input at the boundary
2. Error Handling: Use structured error responses
3. Logging: Log key events for debugging
4. Testing: Unit, integration, and load tests
5. Documentation: Keep docs updated with code changes