I build backend systems that keep working when the business depends on them.

Darwin Herrera

Senior Backend Engineer · Python, Java, AWS

Event-driven services on AWS, real-time and offline-first applications, and migrations of legacy platforms. Six years in production for healthcare, retail, banking and SaaS companies.

Open to senior backend roles and to project work with companies anywhere.

Message me on LinkedIn EmailGitHub
TKD Poomsae Scorer — offline scoring, live on the venue TVCase study
Realtime Events — every screen in sync, liveCase study

Selected work

Two complete systems, from the problem to a running product, and the open-source library behind my architecture.

Everything on GitHub

Taekwondo judges used to score on paper. Now the result is on the TV before the next athlete walks on.

Each judge scores accuracy live and presentation after the form. With five or seven judges the highest and lowest are dropped for each part, and athletes perform two forms: up to 56 numbers per match, once collected by hand.

Offline-first
Every tap is stored on the phone first; a dropped Wi-Fi loses nothing and blocks no one.
Exactly once
Idempotent events and a checksum shared by app and server reconcile every judge's card.
By the rulebook
3, 5 or 7 judges, trimmed averages per part and the tie-break, tested with full matches.
Read the case study Source code
Judge app: technical scoring screen with large deduction buttons for the red and blue athleteJudge app: presentation screen with speed and power, rhythm and tempo, and expression of energy per athlete
Realtime Events on a desktop: the event list with dates, places and attendee counts, and the details of the selected event with its attendeesRealtime Events on a phone: the same event list, with joined and canceled events marked

Realtime Events: everyone sees the same event the moment it changes.

People create, join, leave and cancel events at the same time. Every open screen updates live, and the state stays consistent no matter who acted first.

Domain first
Event lifecycle, permissions and joining rules live in a pure domain layer, behind a FastAPI adapter.
Live by design
HTTP stays the source of truth; one WebSocket channel notifies clients after each successful change, specified with an AsyncAPI contract.
Shipped
Deployed with PostgreSQL and Alembic migrations, 100+ tests above 85% coverage, and a documented path to scale the live channel out.
Read the case study Try the live demoCode: backend ·frontend

bisslog: the use case stays, everything around it changes.

My open-source library for hexagonal architecture in Python. Business rules live in plain use cases; Flask, FastAPI, AWS Lambda, MongoDB or RabbitMQ plug in as adapters, so changing a framework or a database does not mean rewriting the business.

The same separation runs through both projects above. bisslog packages it, with handlers generated from metadata, as seven libraries on PyPI.

How bisslog works Source codePyPI
Animation: a use case in the centre stays the same while the entry point changes from Flask to AWS Lambda, FastAPI, Axum, Express and NestJS, and the adapters change from RabbitMQ and MongoDB to Kafka and SQL Server.
Frame by frame, the entry point, the adapters and even the language change. The use case in the middle does not.

Experience

Six years building backend systems in production, most of them on AWS and in event-driven architectures.

2025 — 2026

Senior Backend Engineer · BairesDev

Remote, for a US healthcare communication platform

  • Sent 10,000+ personalised notifications a day through an event-driven architecture on SNS, SQS, EventBridge and SES.
  • Built Python / FastAPI microservices and ETL pipelines on AWS ECS and Lambda, with idempotency, dead-letter handling and automated retries.
  • Kept automated test coverage above 80% with Pytest, SonarQube and CI/CD.

2022 — 2025

Backend Engineer · SETI

Enterprise integration platform for a 40,000-employee retailer, plus banking clients

  • Created a reusable Spring Boot migration framework that cut development and testing effort by about 80% for a five-person team.
  • Supported 50+ ETL and integration processes, ten of them business-critical.
  • Automated the conversion of 100+ legacy reporting tables, saving about five hours per screen, and moved a legacy Python platform to cloud-native services.

2021 — 2022

Backend Engineer · AI messaging SaaS

Messaging platform for enterprise clients

  • Led the architecture and backend: Python APIs and AWS serverless services with hexagonal, framework-independent components.
  • Integrated an AI-powered workflow with the customer helpdesk and event-driven messaging over SNS, SQS and webhooks.
  • Lowered AWS operating cost by about 25% with a serverless-first design.

2020 — 2021

Python Developer · Freelance

Marketing automation and AI analytics

  • Built CNN models for facial and voice emotion detection, REST APIs, ETL pipelines and scrapers, with React (Next.js) front ends.

AWS Certified Cloud Practitioner · HiveMQ Certified MQTT Associate · B.Sc. Systems and Computer Engineering, National University of Colombia · English (C2), Spanish (native), German (A2)

What I can build for your team

As a member of your engineering team or as a project with a clear scope and a working system at the end.

Backend services and APIs

Python (FastAPI, Flask, Django) or Java (Spring Boot), REST and WebSocket APIs, tested and observable from the first release.

Shown in Realtime Events and TKD Poomsae Scorer

Event-driven systems on AWS

Lambda, ECS, SQS, SNS and EventBridge, with idempotency, retries and dead-letter queues so nothing is lost or sent twice.

10,000+ notifications a day for a healthcare platform

Real-time and offline-first applications

Apps that keep working on unreliable networks and agree with the server the moment they reconnect.

Shown in TKD Poomsae Scorer

Modernization of legacy platforms

Moving legacy systems to cloud-native services step by step, without stopping the business that runs on them.

About 80% less effort with a reusable migration framework

Outside the code

Darwin Herrera holding his engineering diploma in front of the Facultad de Minas building

Systems and Computer Engineer

I graduated from the National University of Colombia in 2024, already working as a backend engineer. Graduation day at the Facultad de Minas.

Darwin Herrera in his black belt and dobok, holding his 1st Dan certificate next to the banner of the National University of Colombia taekwondo club

Taekwondo black belt, 1st Dan

Certified at the National University of Colombia taekwondo club, where I spent two years as an assistant instructor. The same sport is behind TKD Poomsae Scorer. I also practise public speaking with Toastmasters.

Darwin Herrera in a helmet and riding jacket on his red motorcycle, giving a thumbs up on a mountain road

On the road by motorcycle

I travel by motorcycle: long rides through the mountains of Colombia and down to Ecuador.

Writing

All posts

Hiring, or have a system to build?

A short message on LinkedIn about the role or the project is enough to start. I answer every message.

Message me on LinkedIn
darwinherrera1508@gmail.comGitHub