Guillermo Natali Ulla
Software Engineer / Backend Lead at a software consultancy. Backend and infrastructure are my specialty, and I have built several complete products: database, API, frontend and server.
Taking systems to production and keeping them running afterwards
+500,000
Inbound messages per month on the platform I lead
45
Accounts in production on a single instance
3
Systems I designed and still maintain
3
Years of experience building solutions
What I use every day
About
I come from the countryside. As a kid I helped my dad take machines apart: understanding how something worked inside was always the part that hooked me. In 2015 I built my first PC on my own and got into C++ to understand how what I saw on the screen was actually built.
In 2017 I got to Python and everything turned around: any idea I had in my head, I could build quickly and simply. I never let go of that. I taught myself for years, between courses, the terminal and pure logic, and during the pandemic I added web, frontend and frameworks.
In 2022 I started a technical degree and in 2024 I graduated as a Software Development Technician. I am studying engineering in parallel, now in my fifth year. The drive is still the one I had at fifteen: open the "machine" and see how it works.
Skills
Django, Django Ninja and Rails on PostgreSQL. Typed APIs, queues with Sidekiq and Celery, business rules in the database. Today I maintain a multi-tenant platform handling more than 500,000 messages per month.
Docker, Nginx and Caddy, TLS and CI/CD pipelines with GitHub Actions. I run my own server with six services in production and keep deployment reproducible so anyone on the team can do it.
A backend specialist, but I have built several complete products: database, API, frontend in React or Next.js and the server they run on. Skin Studio is one of them, and it is public.
Things that have to coexist on a shared substrate without stepping on each other: clients on one instance, rules in one model, applications on one server. Isolation is not provided by the interface; it comes from the design underneath.
1 instance → N clients
A single instance serves 45 accounts, each with its own WhatsApp number and its own inbox, never seeing another account's conversation.
1 domain → N rules
Business rules lived as unspoken agreements and broke on every exception; now they live in the model, each with its own test.
1 server → N apps
The pattern I use to host six applications in production, this site included. A new app comes in without touching any of the ones already running.
How I work
It is the sequence I follow on every project, and the reason business rules do not break the moment the first exception shows up.
What can happen, what must never happen, and which exceptions already exist even if nobody wrote them down.
I design the model as the problem demands, relational or document-based. Non-negotiable rules live in the data layer: constraints, transactions and schema validation, not in the UI.
One compose per app, a central reverse proxy, automated TLS and CI/CD. Deployment is part of development, not a step handed off to someone else: the team can ship changes the same day.
Update it, respond when something breaks, and revisit decisions when the business changes. Shipping is half the job.
Cases
Clients are named by industry, not by name. Each case has its own page with the problem, the technical decision and the result.
A single instance serves 45 accounts, each with its own WhatsApp number and its own inbox, never seeing another account's conversation.
45
Accounts in production
+500,000
Inbound messages per month
Business rules lived as unspoken agreements and broke on every exception; now they live in the model, each with its own test.
The pattern I use to host six applications in production, this site included. A new app comes in without touching any of the ones already running.
The difference
Stack
A tool makes this list once I have put it in production and kept it running. What I am still learning, I say so.
| Tool | What for | Where |
|---|---|---|
| PostgreSQL | Atomic logic and constraints in the database, not in the application. Advanced SQL. | Where: Omnichannel messaging · Skin Studio |
| MySQL, MongoDB, Firebase | Relational or document-based, whichever the model calls for. Firebase for auth and real-time data when a custom backend is not justified. | Where: Purchasing API · audit projects |
| Python, Django | DRF and Django Ninja for typed APIs with Pydantic. | Where: Skin Studio |
| Ruby on Rails | I extend and maintain an open source platform in production. | Where: Omnichannel messaging |
| Docker, Nginx, Caddy | One compose per app, a central reverse proxy, TLS with Certbot. | Where: Multi-app VPS |
| GitHub Actions | Automated build and deployment pipelines to my own servers. | Where: Multi-app VPS |
| Sidekiq, Celery, Redis | Everything that must not block a request. | Where: Omnichannel messaging · Skin Studio |
| Integrations | WhatsApp Cloud API, MercadoPago, Google Calendar, n8n, Evolution API. | Where: Omnichannel messaging · Skin Studio |
| JavaScript, React, Next.js | The frontend of the products I built end to end, in TypeScript. React and Vite where it already existed. | Where: Skin Studio · this site |
| Go | Growing. Not in production yet. | Where: — |
Experience
October 2025 — today
Software consultancy · remote
Leading the backend of a multi-tenant platform in production: deciding the architecture, keeping it up under load and responding when something breaks.
January — October 2025
E-commerce in production
Ten months building modules and custom templates reusable across projects. It was my first contact with real development, deployment and infrastructure cycles.
2022 — today
Software Development Technician, ISBL (graduated 2024) · Information Systems Engineering, UAI — 5th year
The foundations I use every day: data modeling, algorithms and relational databases.
2015 — 2021
C++, Python, the terminal and pure logic
Seven years learning on my own, with nobody to correct me. That is where I picked up the habit of reading other people's code until I understand it, which is what I do today when I extend a platform I did not write.
I design it, build it end to end and take ownership of keeping it running. Write to me and let's talk. I reply the same day.