# David Martínez — Backend Engineer

> I'm a freelance backend engineer specializing in NestJS, TypeScript, AWS, and event-driven distributed systems. 4+ years shipping production-grade SaaS backends. Based in Honduras (CST), available 20–30 hrs/week for US and EU timezones.

I'm David Martínez (David Daniel Membreño Martínez). I build reliable, observable, fault-tolerant systems for SaaS teams. My focus is the engineering work that decides whether a SaaS scales past its first 1000 customers: reliability, idempotency, observability, and graceful failure.

## What I do

- **Backend APIs that scale**: Production-grade REST and GraphQL APIs with NestJS and Node.js. Multi-tenant, well-tested, observable.
- **Event-driven architecture**: Async workflows, the Outbox Pattern, idempotency, retries with exponential backoff. AWS SQS, Redis, Lambda.
- **Production firefighting**: Race conditions, duplicate records, silent job failures, slow queries. I diagnose the bug and add the observability to catch the next one.

## My tech stack

- **Languages & Runtime**: TypeScript, Node.js, JavaScript
- **Backend & APIs**: NestJS, Express, GraphQL, REST, TypeORM
- **Data & Infra**: PostgreSQL, Redis, AWS (SQS, S3, RDS, Lambda), Docker
- **Architecture**: Event-driven, Microservices, Outbox Pattern, Multi-tenant
- **Observability & Testing**: OpenTelemetry, Pino, Jest

## Selected work

- **Distributed Notification System with Outbox Pattern** (2025, GraphxSource) — Multi-tenant SaaS. I built an async dispatcher with transactional persistence, retries with exponential backoff, and distributed tracing. Result: 99.9% event delivery reliability, zero silent failures.
- **Fault-Tolerant Order Processing** (2025, GraphxSource) — High-volume transactional system. I built the retry system with idempotency, partial indexes, pessimistic locking, and server-side billing validation. Result: 40% reduction in processing failures, ~0 duplicate records.
- **iOBOT — Omnichannel CRM Backend** (2024, Authcode) — B2B SaaS unifying WhatsApp, Instagram, Messenger into a single CRM pipeline. I built event-driven workflows on AWS, Socket.io for real-time, and an OpenAI chatbot layer.

## Production metrics I've shipped

- 99.9% event delivery reliability in production
- 40% reduction in order processing failures
- 50% reduction in incident resolution time
- 4+ years building distributed systems

## How to reach me

- Email: contact@davidmrtz.me
- Site: https://davidmrtz.me
- GitHub: https://github.com/DavidMrtz8
- LinkedIn: https://www.linkedin.com/in/david-daniel-membre%C3%B1o-mart%C3%ADnez-961053322
- Book a call: https://cal.com/davidmrtz/20-min-call
- Location: San Pedro Sula, Honduras (CST timezone)
- Availability: 20–30 hrs/week, comfortable with US and EU timezones

## Key resources

- [My portfolio site](https://davidmrtz.me): Full case studies, services, stack, contact
- [Services (machine-readable)](https://davidmrtz.me/services.md): Structured service offerings
- [CV (PDF)](https://davidmrtz.me/cv.pdf): Full resume
- [Sitemap](https://davidmrtz.me/sitemap-index.xml)