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F16: RESTful Delivery, Scheduling, Retry & Template APIs (NTF-098, NTF-099, NTF-100, NTF-101, NTF-103, NTF-105, NTF-109, NTF-110) ​

1. Technical Summary & Behavior ​

Unified REST API endpoints for dispatching, status tracking, delayed scheduling, DLQ reprocessing, and health checks.

  • Feature ID: F16
  • Source Files: backend/src/api/app.py
  • Key Implementation Lines: api/app.py:107-140 (Health & Ready), api/app.py:192-315 (Delivery API), api/app.py:319-365 (Schedule API), api/app.py:371-450 (Retry & DLQ API), api/app.py:481-515 (Template API)
  • Data & Schema: FastAPI ASGI routes with Pydantic request/response models and OpenAPI documentation

2. Architecture & Data Flow ​

3. Sequence Flow Diagram ​

4. Failure Path & Resilience Diagram ​

5. Security & Edge Case Considerations ​

  • Tenant Isolation: Every query and operation scopes explicitly to tenant_id. Cross-tenant data leakage is structurally prevented.
  • Data Sanitization & Encryption: Sensitive recipient tokens and provider secrets are encrypted with Fernet and masked on all outputs.
  • Idempotency: Requests enforce unique constraint hashes to prevent duplicate dispatch under network retries.

6. Say It Out Loud (Spoken Interview Script) ​

"I implemented the core REST API layer in backend/src/api/app.py using FastAPI to provide a clean, asynchronous interface for our entire microservice architecture. The API exposes unified endpoints: /api/v1/delivery for ingesting notifications across any channel, /api/v1/schedule for future-dated dispatch, /api/v1/notifications/{id}/retry and /replay for operator interventions, and /api/v1/dlq/reprocess for batch dead-letter recovery. The application includes liveness (/healthz) and readiness (/readyz) probes that verify database connectivity for Kubernetes orchestration. I configured global middleware that injects a unique X-Request-ID into every HTTP response header and formats all unhandled exceptions into structured JSON error envelopes. I chose FastAPI over Flask or Django because its asynchronous nature and Pydantic integration offer high throughput and automatic Swagger documentation. If a client submits malformed data, FastAPI returns a detailed 422 Unprocessable Entity response highlighting the invalid parameter. The limitation is that our API currently handles ingress synchronously; at 50,000 requests per second, I would place an API Gateway and an ingestion queue buffer like Kafka in front of these endpoints."