Article 08: Gateway Filters & Centralized Routing

1. Objective

Learn how to use filters in API Gateway for logging, authentication, and request modification.

2. Key Concepts

• Global filters
• Route-specific filters
• Pre and Post filters

3. Why Filters Matter

Common needs:

• Logging
• Authentication
• Header modification
• Rate limiting

4. Simple Global Filter Example

@Component
public class LoggingFilter implements GlobalFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        System.out.println("Request Path: " + exchange.getRequest().getPath());
        return chain.filter(exchange);
    }
}

5. Route-Specific Filter

filters:
  - AddRequestHeader=X-Request-Source, Gateway

6. Centralized Routing Benefits

• Easy changes
• No client impact
• Versioning support

7. Common Mistakes

• Heavy logic in filters
• Ignoring performance impact
• No fallback handling

8. Interview Notes

• Filters run before/after routing
• Gateway is not a replacement for service logic

9. Summary

Filters make API Gateway powerful and flexible.

10. What’s Next

Add centralized configuration using Spring Cloud Config.