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External Service Resilience

This document outlines best practices to improve resilience and reliability when communicating with external services (e.g., PayPal, third-party APIs) in a Java Spring Boot environment.

1. Overview​

Modern microservices often rely on external systems such as payment gateways, identity providers, or third-party APIs. These systems may fail or exhibit latency issues. Proper resilience strategies protect internal systems from cascading failures.

2. Common External Failures​

  • Network timeouts or DNS resolution issues
  • Rate limiting or throttling
  • API schema changes
  • Unavailability (downtime or maintenance)
  • Slow responses or high latency

3. Resilience Strategies​

3.1 Timeout Configuration​

  • Use RestTemplate/WebClient with well-defined connection/read timeouts.
  • Prevent hanging threads.
WebClient.builder()
  .baseUrl("https://api.paypal.com")
  .clientConnector(new ReactorClientHttpConnector(
      HttpClient.create()
          .responseTimeout(Duration.ofSeconds(5))
  ))
  .build();

3.2 Retries (with Backoff)​

  • Use RetryTemplate or resilience4j-retry with exponential backoff.
  • Avoid infinite retries — use maxAttempts.
resilience4j.retry.instances.paypalRetry:
  maxAttempts: 3
  waitDuration: 2s
  exponentialBackoff:
    multiplier: 2.0

3.3 Circuit Breakers​

  • Prevent overload and cascading failures (see detailed file).
  • Fallback to cached or default responses.

3.4 Isolation (Bulkheads)​

  • Use separate thread pools or queues for external service calls.

3.5 Monitoring & Alerts​

  • Set up alerts for elevated error rates or slow responses.
  • Use tools like Prometheus + Grafana or ELK.

4. Fallback Scenarios​

  • Return default data (e.g., "Payment pending").
  • Queue for retry or escalate to manual review.
  • Log errors with correlation IDs.

5. Best Practices​

  • Validate third-party contracts with contract tests.
  • Simulate outages using chaos engineering.
  • Use API gateways to apply policies centrally.
  • Document Version: 1.0
  • Date: 2025-06-24
  • Author: ArturChernets