Error Handling & Resilience Patterns

[Sakeeb91]

Priority

P0

Story Points

8

Dependencies

Depends on #6 (Shared Libraries), #7 (API Gateway)

Summary

Establish standardized error handling, retry logic, circuit breakers, and resilience patterns across all services to ensure graceful degradation, meaningful error messages, and system stability under failure conditions.

Background

Currently, services have inconsistent error handling:

• Basic try-catch blocks without structured error types
• No retry logic for transient failures
• No circuit breakers for external dependencies
• Inconsistent error response formats
• Limited error context for debugging
• No correlation IDs for request tracing

Acceptance Criteria

• Standardized error response format across all services
• Custom error types (ValidationError, DatabaseError, AuthError, etc.)
• Circuit breaker pattern for external service calls
• Retry logic with exponential backoff for transient failures
• Correlation IDs propagated through all service calls
• Graceful degradation strategies documented
• Error middleware for Express/HTTP servers
• Structured error logging with context
• Dead letter queue for failed async jobs
• Error recovery documentation and runbooks

Key Features

Standard Error Response:

{
  "error": {
    "code": "AUTH_INVALID_TOKEN",
    "message": "Invalid or expired token",
    "details": {},
    "requestId": "uuid",
    "timestamp": "ISO 8601"
  }
}

Custom Error Types:

• ValidationError (400)
• AuthenticationError (401)
• AuthorizationError (403)
• NotFoundError (404)
• ConflictError (409)
• DatabaseError (500)
• ExternalServiceError (502)
• RateLimitError (429)

Resilience Patterns:

• Circuit breaker with OPEN/HALF_OPEN/CLOSED states
• Retry with exponential backoff
• Correlation ID propagation
• Graceful shutdown handlers

Related Issues

• Issue Shared Libraries Package Setup #6: Shared Libraries Package Setup
• Issue API Gateway Service #7: API Gateway Service
• Issue Monitoring & Observability Setup #8: Monitoring & Observability Setup

Documentation

Full technical specification available in: docs/issues/0008-error-handling-resilience-patterns.md