Hi, I'm
Adelys AlbertoBelen CarvajalTechnical Lead & Staff Software Engineer
From bare-metal Linux infrastructure to high-concurrency fintech microservices. I design systems that scale and lead teams that deliver.
Engineer with 12+ years of experience who understands the machine from kernel to presentation layer. Platform architect, team mentor, and passionate about well-crafted software.
12+Years of experience
YC S22Backend Architect
CloudMicroservices & DDD
FintechScale & high availability
About me
An engineer who thinks in systems, not just in code
I started my career managing physical infrastructure: Linux servers, 5km networks, VoIP with Asterisk, and virtualization systems with Docker and LXC. That foundation gave me something few product developers have: understanding what really happens underneath the stack.
Over the years I evolved toward product development and software architecture. Today I design and build high-concurrency fintech platforms, enterprise component libraries, and systems that survive scale. I've led technical teams, defined code standards, and made architectural decisions in contexts where mistakes are expensive.
I'm passionate about the intersection between technical excellence and real business impact. The most elegant code is the one that solves the right problem, that the team can maintain, and that doesn't need heroics to survive in production.
Engineering Philosophy
How I think about software
I don't have off-the-shelf thinking frameworks. I have principles forged in real projects, with real teams, in real production.
Simple scales better
Accidental complexity is the greatest enemy of systems. Before adding an abstraction, I ask myself if I need it today or if I'm building it for future convenience that may never come.
Architecture is communication
Every architectural decision communicates something about how the team understands the business. DDD, Vertical Slicing, Hexagonal Architecture are not technical tools; they are shared languages.
DX powers UX
A team with good tools, good documentation, and a good feedback loop delivers better software faster. Investing in Developer Experience isn't luxury; it's strategy.
Failure has real cost
In fintech and high-concurrency systems, bugs aren't statistics. That's why I design with failure in mind: Result Pattern, circuit breakers, idempotency, monitoring from day one.
Mentoring multiplies impact
I can write the best code on the team or I can make the entire team write better code. The second option always wins. Knowledge that isn't shared doesn't scale.
Software is for people
Every line of code I write exists because someone has a problem to solve. That's never forgotten. Not when I design APIs, not when I review PRs, not when I define standards.
Technical Leadership
How I lead engineering teams
I've led technical teams in very different contexts: YC-backed startups, national-scale fintechs, and product consultancies. What I learned is that technical leadership isn't about having all the answers. It's about creating the environment where the team can find them.
Clear architectural decisions
I document technical decisions (Architecture Decision Records), explain the reasoning, and open the discussion before writing a single line of code. Teams that understand the why, execute better.
Code reviews that teach
A good code review isn't about finding errors. It's about transferring knowledge, aligning criteria, and raising the team's level. Every PR is an opportunity for collective learning.
Active technical debt reduction
Technical debt doesn't disappear by ignoring it. I manage it as a real backlog: prioritize, measure its impact on velocity, and systematically dedicate capacity. No heroics, no crises.
Standards that liberate
A good set of code standards doesn't limit creativity, it liberates it. When the team doesn't need to debate the how, they can focus on the what and the why.
Experience
Projects that made an impact
BETWEEN Technology Group
Technical Lead — Frontend
From entropy to order: standardizing the frontend of a leading technology consultancy.
- Designed and led the architecture of an internal shared Component Library across multiple projects, reducing new interface development time by 40%.
- Established code standards (strict TypeScript, Clean Code, SOLID, CSS Modules) adopted as the de facto standard in client projects.
- Led the architectural migration of legacy projects to React 18 with Vertical Slice Architecture and clear separation of UI, domain, and infrastructure layers.
- Mentored mid-level engineers, accelerating their growth to senior roles through systematic reviews and directed pair programming.
ReactTypeScriptNestJSCSS ModulesStorybookGitHub Actions
Ping
Backend Engineer
Building the billing and payments infrastructure for a Y Combinator-backed fintech.
- Designed and implemented the invoice management service on a distributed microservices architecture with Node.js, Redis, and AWS.
- Built the internal backoffice system for real-time transaction and user management with WebSockets.
- Worked in a high technical-demand, fast-velocity environment typical of a YC startup in accelerated growth stage.
Node.jsNestJSRedisAWSWebSocketsPostgreSQL
MODO
Senior Full Stack Engineer
Integrating a national payment ecosystem with Argentina's top e-commerce platforms.
- Led payment integrations with TiendaNube, VTEX, WooCommerce, and Spreedly, enabling millions of users to pay with MODO at the country's top marketplaces.
- Actively participated in the migration from monolith to Microservices architecture with Hexagonal Architecture and DDD.
- Worked with distributed teams on a product with millions of active users and critical availability requirements (99.9% SLA).
ReactNode.jsMicroservicesHexagonal ArchitectureDDDPostgreSQL
Personal Pay (Telecom) & SimTLiX
Backend Engineer — Serverless & Cloud
Event-driven serverless architecture for telco-scale financial services platforms.
- Designed and implemented complete Serverless architectures with AWS Lambda, SQS/SNS, DynamoDB, and Terraform.
- Built asynchronous event processing pipelines for financial transactions with idempotency guarantees.
- Defined Infrastructure as Code (IaC) with Terraform, enabling reproducible and auditable deployments.
AWS LambdaSQSSNSDynamoDBTerraformNode.jsServerless Framework
Skills
Tools and expertise
Architecture
- Clean Architecture
- DDD
- Hexagonal
- Vertical Slice
- Event-Driven
- Microservices
- SOLID
- Result Pattern
Backend & Cloud
- Node.js
- NestJS
- Express
- Hapi.js
- AWS Lambda
- SQS/SNS
- DynamoDB
- PostgreSQL
- MongoDB
- Redis
- Terraform
Frontend & Mobile
- React
- TypeScript
- Astro
- Next.js
- React Native
- Zustand
- CSS Modules
- Design Systems
DevOps & Infrastructure
- Docker
- NGINX
- CI/CD
- GitHub Actions
- Jenkins
- Linux
- LXC
- TCP/IP Networking
Leadership
- Tech Lead
- Mentoring
- Code Reviews
- Architecture RFCs
- Team Building
- ADRs
What I believe
My engineering manifesto
Software exists to solve real people's problems.
Simple scales better than sophisticated.
Architecture is the team's communication about the domain.
Tests aren't optional; they're evidence of understanding.
Mentoring multiplies impact more than any line of code.
Poorly managed technical debt is financial debt in disguise.
A team with great DX always delivers better UX.
Code that needs a hero to survive in production has already failed.
Career Timeline
12+ years of continuous evolution
- 2012
The beginning: SysAdmin & Networks
Linux server administration, 5km physical networks, VoIP with Asterisk, Docker and LXC. The foundation that changed everything.
- 2015
Software development
Transition to product development. First web projects with Node.js and React.
- 2019
Senior Engineer & Olympiad Finalist
Finalist at the Computer Science Olympiad. Projects of increasing complexity in backend and architecture.
- 2020
Serverless Architecture
SimTLiX and Personal Pay (Telecom). Event-driven architecture with AWS Lambda, SQS/SNS, DynamoDB and Terraform.
- 2021
MODO — Fintech at scale
Payment integrations with Argentina's top e-commerce platforms. Migration from monolith to microservices with DDD and Hexagonal Architecture.
- 2022
Ping — Y Combinator S22
Backend engineer at YC-backed fintech startup. Billing microservices and payments infrastructure.
- 2023
Technical Lead @ BETWEEN
Technical leadership at one of Spain's top technology consultancies. Component Library, standards, and mentoring.
- Now
Madrid · Looking for the next challenge
Available for Technical Lead, Staff Engineer, or Principal Engineer roles at product companies, startups, or scaleups.
Contact
Let's build something extraordinary
Currently leading engineering teams at BETWEEN. Open to exploring high-impact challenges as a Tech Lead, Staff Engineer, or Principal Engineer. Working from Madrid with international teams.
Based in Madrid, Spain — CET/CEST (UTC+1/+2)
Tech Lead @ BETWEEN · Open to high-impact roles