Interview question

How do you manage configuration across different environments in Spring Boot? Spring Boot में different environments के लिए configuration कैसे manage करते हैं?

Answer

Use Spring Profiles for environment-specific configuration. Externalize configuration using application-{profile}.yml or environment variables. Implement ConfigServer for centralized management in microservices.

// application.yml (base)
spring:
  application:
    name: app
  profiles:
    active: ${SPRING_PROFILES_ACTIVE:dev}

// application-dev.yml
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/appdev
    password: dev123
  jpa:
    hibernate:
      ddl-auto: create-drop
  cache:
    type: simple

// application-prod.yml
spring:
  datasource:
    url: jdbc:mysql://mysql-prod:3306/appprod
    password: ${DB_PASSWORD}  # From environment
  jpa:
    hibernate:
      ddl-auto: validate
  cache:
    type: redis
    redis:
      host: ${REDIS_HOST}
      port: ${REDIS_PORT}

logging:
  level:
    root: WARN

// Programmatic Profile Usage
@Configuration
@Profile('prod')
public class ProdConfig {
    @Bean
    public DataSource prodDataSource() {
        // Production database config
    }
}

@Configuration
@Profile('dev')
public class DevConfig {
    @Bean
    public DataSource devDataSource() {
        // H2 in-memory for testing
    }
}

// Spring Cloud Config Server (Centralized)
// config-server-pom.xml
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-config-server</artifactId>
</dependency>

// Config Server application.yml
spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/config-repo
          searchPaths: configs/**

// Config Client
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-config</artifactId>
</dependency>

// bootstrap.yml (Config Client)
spring:
  cloud:
    config:
      uri: http://config-server:8888
      name: app
      profile: prod

// Accessing Config
@Component
public class AppConfig {
    @Value('${database.host}')
    private String databaseHost;
    
    @Value('${cache.ttl:3600}')
    private int cacheTtl;  // Default value
}

// Runtime Property Refresh
@RestController
@RefreshScope  // Allows refresh without restart
public class ConfigController {
    @Value('${feature.flag}')
    private boolean featureFlag;
    
    // POST /actuator/refresh to reload
}

// Environment Variables (Priority)
// 1. Command line arguments
// 2. System properties
// 3. OS environment variables
// 4. application-{profile}.yml
// 5. application.yml

// Running with different profiles
java -jar app.jar --spring.profiles.active=prod
java -Dspring.profiles.active=staging -jar app.jar
export SPRING_PROFILES_ACTIVE=prod && java -jar app.jar

Configuration Management:

Profiles का use करना:
- application-dev.yml
- application-prod.yml
- application-staging.yml

Activation:
spring.profiles.active=prod

Environment Variables:
${DATABASE_URL}
${API_KEY}

Config Server:
- Centralized configuration
- Multiple microservices
- Version control (Git)
- Runtime refresh

@RefreshScope:
- Restart के बिना config update
- POST /actuator/refresh

Priority Order:
1. Command line args
2. System properties
3. Environment variables
4. profile-specific YAML
5. Default YAML

Best Practice:
- Secrets: Environment variables
- Configuration: Config Server
- Defaults: application.yml

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