Fernando Guillen

Building Business Success: Web Projects and Technical Architectures

Hello. I am Fernando. I am originally from Spain, but I've lived in Berlin for the last decade. I am an experienced full-stack web developer with more than 20 years of substantial background building big and small web products. I can help you build the web product and technical architecture your business needs.

Full-stack senior web developer specializing in Ruby on Rails and associated technologies.

Coming from Spain, I’ve been in Berlin for a long time. I’m a Ruby lover, I draw children’s books, and I’ve been building video games since 2022. I’ve been into Rails since version 0.8, I was one of the organizers of Euruko Barcelona 2009. Matz was wearing his socks when the airplane lost his baggage at Euruko Poland. I had postal correspondence with Why the Lucky Stiff before his disappearance. I’m the creator of fantasy, an open-source library designed to introduce children to programming using Ruby.

I started my programming career at 11 years old using the BASIC language of MSX. I have programmed in Assembler, C, C++, Pascal, Visual Basic, and Java. I moved to Rails after being captivated by its community and culture (make the programmer happy). I also have extensive exposure to Python, JS, C#, and GDScript. I started working for a big company, but most of my career has been in startups. My last adventure was co-founding a company here in Berlin, watching it grow as CTO from 2 employees to 80 in 7 years. I went through investment rounds, technical audits, and finally a successful exit in 2022.

I’ve seen things you people wouldn’t believe. MySQL tables with over 5 billion records. Databases surpassing 16TB. Schema migrations in production that last for days, without downtime. Rails architectures with over 30 services, hundreds of servers, and dozens of databases. AWS monthly invoices over €60K. Setting up 30 web applications running locally to replicate production workflows. Making code changes directly on production servers. Battling against click farms. Debugging JavaScript errors that only occur for users in China.

I am more into Minitest than Rspec, double quotes than single quotes, Authlogic than Devise, “if” than “unless”, long variable names than abbreviations, raw JS than TypeScript, raw CSS than Sass, Bootstrap than Tailwind, REST than GraphQL, VueJS than React, Ubuntu than Debian, nano than vim, Docker Compose than Swarm, and I am afraid of Kubernetes. I prefer Darkmode over Lightmode. I prefer Sundays over Saturdays, rivers over beaches, 2D games over 3D, a good book over a TV series, and silence over music.

My current main interest is integrating AI LLMs (OpenAI) into real-world use cases or business workflows. I’m curious about what the people at Hugging Face are offering and how I can make use of it. I am building an application to leverage an LLM for natural language conversations with my database (RAG architecture), using Ruby and the limited libraries available for this. On my radar for my next research is experimenting with Kamal for deployment orchestration.

I specialize in getting web projects off the ground, guiding them from design concept to fully functional applications. I focus on ensuring production quality while maintaining fast development cycles and rapid feedback loops (deliver fast and iterate). As a senior developer position, I have worked for startups, large corporations, and personal entrepreneurial ventures, contributing either as an individual developer or as part of engineering teams of varying sizes, often taking on leadership roles and influencing architectural decisions.

Most recently, as Co-founder and CTO of a rapidly growing technology company, I was hands-on directing the implementation from scratch of an architecture that now supports more than 100K requests/min and a business of 8 figures yearly—leading the technology decisions of a team of ~80 members. The architecture was acquired in 2022 by an international company.

While my primary expertise lies in Rails applications, I have solid exposure to the entire web development stack.

Over time, I’ve been responsible for a range of tasks, including prototyping, implementing CI-based deployment processes, managing cloud-based servers, front-end development, agile/scrum team management, collaboration with product teams, C-level executive decision-making, microservices architecture implementation, handling high-traffic sites, fraud prevention, performance monitoring, observability and telemetry, autoscaling, managing terabyte-sized databases, down-time-less extensive database migrations, and API design.

I have extensive experience with various languages such as Python, C#, and Java, as well as familiarity with modern JS frameworks like ReactJS and VueJS.

… However, Ruby remains what I enjoy working the most.

Beyond my technical skills, I possess a keen understanding of business needs, demonstrating the ability to make pragmatic decisions and prioritize business growth and success. I excel at collaborating closely with product, sales, and leadership teams, offering alternatives when necessary, and knowing when to make compromises.

Throughout my career, I’ve had the privilege of working alongside incredibly talented individuals from whom I’ve learned and grown. I owe much of my knowledge and skills to the exceptional teams I’ve been a part of and the broader open-source and web development communities, particularly those centered around Ruby.

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