Example 18: API Error Handling (unified error contract)

[patterncatalyst]

Chapter

_docs/18-appendix-e-errors.md — API Error Handling

Example Path

examples/18-errors/

What to demonstrate

• Unified error shape: code, message, trace id, retryable flag, field details
• Same contract across REST, gRPC, GraphQL, and Kafka
• Retry-storm controls
• Trace ID propagation in error responses

Stack

• Infra: Podman — Kafka + LGTM
• Language: Python (FastAPI + grpcio + Strawberry + aiokafka)
• Priority: Medium

Deliverables

• compose.yaml
• Service demonstrating errors across all 4 protocols
• README.md
• verify.sh
• Flip chapter footer to verified