01Event-driven reservation enginePersonal project

Flight Booking Microservices

Event-Driven Saga Transaction Engine

6-service distributed flight booking with database-per-service isolation, Saga compensation, and end-to-end tracing.

View source on GitHub

NestJSTypeScriptPostgreSQLRedisRabbitMQDockerOTel

6 Microservices

Saga Orchestration

Redis Locks

OpenTelemetry

The engineering problem

Core Challenge

Preventing double-booking across distributed services without 2PC deadlock overhead.

Architecture Solution

Redis mutex locking with TTL + Saga orchestrator issuing compensating unlock events on payment failure.

Resilience Guardrail

Idempotency-Key header required; RabbitMQ dead-letter queues for deterministic replay.

Service topology & IPC protocols

API Gateway (Envoy)

Reverse proxy, rate limiting, x-request-id

HTTP / REST

Auth Service

JWT issuance, refresh token rotation, RBAC

gRPC

Flight Inventory

Seat catalogue, Redis mutex lock with TTL

PostgreSQL + Redis

Booking Coordinator

Saga state machine orchestrator

RabbitMQ / AMQP

Payment Service

Stripe/Tranglo idempotency webhook handler

HTTPS Webhook

Notification Service

Async ticket generator & PDF dispatcher

RabbitMQ Consumer

API Gateway — rate limiting & correlation ID injection
Auth — JWT with RBAC & refresh token rotation
Flights — inventory search with Redis reservation locks
Bookings — Saga coordinator for seat holds
Payments — idempotent webhook processing
Notifications — async queues via RabbitMQ

Canonical event / payload contract

application/json

{
  "eventId": "evt_98319f8a",
  "eventType": "booking.payment_failed",
  "aggregateId": "bk_778102",
  "timestamp": "2026-09-01T14:32:00.000Z",
  "correlationId": "trace_9921fa4b",
  "payload": {
    "bookingId": "bk_778102",
    "seatNumber": "24A",
    "reason": "CARD_DECLINED",
    "actionRequired": "COMPENSATE_UNLOCK_SEAT"
  }
}

Resilience & high availability

Saga Orchestration: Automatic backward rollback releasing seat locks upon payment authorization failure.

Idempotency Guard: All mutating payment endpoints require UUIDv4 Idempotency-Key in Redis.

Dead-Letter Queues (DLQ): RabbitMQ consumer errors routed to DLQ with exponential backoff and replay.

Distributed Tracing: OpenTelemetry spans injected at gateway and propagated across IPC boundaries.

Compensating Saga transactionsDatabase-per-service isolationOpenTelemetry distributed tracing

Next case study

Ride-Sharing Platform (Go + gRPC)

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