Patricio Diego Balenzuela, Developer in Lomas de Zamora, Buenos Aires Province, Argentina
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Patricio Diego Balenzuela

Full-stack Developer

Lomas de Zamora, Buenos Aires Province, Argentina

Toptal member since March 14, 2016

Bio

Patricio considers himself a passionate and dedicated professional and mentor who pays close attention to detail and embraces theory and best practices, aiming to deliver the highest quality while balancing deadlines and business objectives. As a developer, he is always learning new things and technologies. As a leader, Patricio is excellent at identifying his team's strengths and weaknesses and helping them succeed.

Portfolio

Sensible
Node.js, TypeScript, Amazon DynamoDB, Amazon Web Services (AWS), AWS Lambda...
Hire Bus, LLC
TypeScript, Node.js, MySQL, Docker, Amazon Web Services (AWS), APIs...
Volvo Car
React, JavaScript, TypeScript, CSS, HTML, Node.js, MySQL, Microservices...

Experience

  • Full-stack - 20 years
  • Node.js - 12 years
  • Microservices - 11 years
  • React - 11 years
  • Test-driven Development (TDD) - 11 years
  • TypeScript - 7 years
  • Amazon Web Services (AWS) - 7 years
  • Serverless - 4 years

Preferred Environment

React, Node.js, TypeScript

The most amazing...

...project I've worked on enabled my newly formed team to deliver a critical feature in record time, turning the company into the best in the market.

Work Experience

Senior Back-end & Infrastructure Engineer

2024 - PRESENT
Sensible
  • Migrated the end-to-end test suite from Cypress to Playwright, restructuring tests using fixture-based project dependencies and the Page Object Model, eliminating flaky tests and enabling safe parallel execution.
  • Migrated the back-end test suite from Jest to Vitest and the package manager from npm to pnpm, unifying the TypeScript toolchain, eliminating phantom dependency risk, and hardening the dependency install surface against supply chain attacks.
  • Designed and implemented a distributed two-tier rate limiting system for external OCR service calls (AWS Textract) using Redis and atomic Lua scripts—eliminating Lambda timeout errors under concurrent load while enforcing per-account fairness.
  • Built the public REST API for the email processors feature across five endpoints—including environment-based routing via email address and full CRUD for processor configuration—taking sole ownership from architecture design through implementation.
  • Instrumented extraction pipelines to track per-extraction cost across four OCR providers and multiple LLM pricing models, enabling margin analysis and anomaly detection per customer and document type for the first time.
  • Introduced Zod schema validation to the API validation layer alongside AJV, enabling incremental endpoint-by-endpoint migration with type-safe schemas and 100% test coverage on all new code.
  • Added a time-budget mechanism to the DynamoDB pagination layer to prevent Lambda timeouts on large result sets, converting silent 30-second failures into partial results with cursor-based resumption.
  • Led the back-end infrastructure migration from SST v2 (CloudFormation) to SST v3, restructuring to a modular one-resource-per-file monorepo using pnpm workspaces.
  • Configured a GitHub Actions workflow for AI-powered code review, enforcing defined style rules—low and medium severity findings posted as inline comments, high severity findings submitted as change requests.
Technologies: Node.js, TypeScript, Amazon DynamoDB, Amazon Web Services (AWS), AWS Lambda, SST, Serverless, GitHub Actions, Docker, Test-driven Development (TDD), Playwright, Amazon Simple Queue Service (SQS), Amazon Simple Notification Service (SNS), Redis, Large Language Models (LLMs), Artificial Intelligence (AI), Scrum, Linux, Continuous Integration (CI), Cloudflare, HIPAA Compliance, Express.js, NoSQL

Staff Engineer & Engineering Coach

2023 - 2024
Hire Bus, LLC
  • Assessed and redesigned the foundational architecture across the full stack, establishing coding standards, API design guidelines, and code review procedures from scratch.
  • Designed and implemented a full testing pyramid (unit, integration, and E2E) across front end and back end, enabling confident deployments and reducing regression risk.
  • Built the E2E test suite using Playwright and introduced the repository pattern to allow isolated, maintainable database testing.
  • Introduced contract tests to validate integrations with external systems, catching interface mismatches before they reached production.
  • Refactored the existing API into a well-defined RESTful API, aligning routes, HTTP methods, and response shapes with REST best practices.
  • Set up CI/CD pipelines on GitHub Actions, automating test execution and deployments across environments.
  • Coached the development team on Agile methodologies—story point estimation, walk-the-board stand-ups, structured retrospectives, and backlog refinement—improving delivery predictability.
  • Consolidated the dependency tree by removing redundant packages and standardizing on a core set of well-maintained libraries.
Technologies: TypeScript, Node.js, MySQL, Docker, Amazon Web Services (AWS), APIs, Test-driven Development (TDD), Playwright, AWS Lambda, React, API Integration, Storybook, Next.js, Serverless, Large Language Models (LLMs), Artificial Intelligence (AI), Prompt Engineering, SST, Scrum, Linux, Continuous Integration (CI), Redis, Express.js

Front-end Developer

2022 - 2023
Volvo Car
  • Worked on feature discovery, analysis, design, and implementation.
  • Managed performance tuning of UI components and network calls.
  • Moved away from functional domain design in favor of domain-driven design.
  • Fostered team self-awareness and discovery by implementing auto-regulated retrospective meetings.
  • Created test automation by designing a testing pyramid covering the whole system. This included API tests, UI E2E tests, repository tests, etc.
  • Utilized GitHub discussions for feature and technical discussions.
  • Completed the implementation of connected-retail-ui npm UI library, a React library that provided basic UI components.
Technologies: React, JavaScript, TypeScript, CSS, HTML, Node.js, MySQL, Microservices, Amazon Web Services (AWS), GraphQL, Redis, REST, Jest, Test-driven Development (TDD), Scrum, HTML5, CSS3, Linux, Continuous Integration (CI)

Development Lead

2021 - 2022
Tatango
  • Acted as a lead developer, made technical decisions, and interacted with the business to define requirements and create user stories.
  • Conducted the different Scrum ceremonies, guided and mentored the team, unblocking problems, and managed the Sprint board.
  • Helped the business achieve its goals by discovering what tools it needed and applying continuous integration and incremental feature enhancements.
  • Designed and led the SMS and MMS enhancements project, the core feature of the company, delivering right on time and almost without any errors.
  • Designed and implemented database tests, including them as part of the CI/CD pipeline.
Technologies: React, Node.js, TypeScript, Amazon Web Services (AWS), Docker, APIs, Storybook, PostgreSQL, Full-stack, Serverless, AWS Lambda, Jest, Test-driven Development (TDD), SQL, Scrum, HTML5, CSS3, Linux, Continuous Integration (CI), Express.js

Development Lead

2019 - 2021
Interview Stream
  • Designed and implemented microservices with Python.
  • Developed team best practices, a collaborative spirit, and continuous team improvement practices.
  • Applied Agile methodologies to discover the right way to build the right product. Used trunk-based development and deployed minimal incremental features by the end of each sprint.
Technologies: Docker, Amazon Web Services (AWS), Datadog, Bugsnag, Python, React, REST, GraphQL, TypeScript, APIs, PostgreSQL, Full-stack, PHP, API Integration, Jest, Test-driven Development (TDD), Microservices, SQL, Scrum, HTML5, CSS3, Linux, Express.js

Lead Developer

2018 - 2019
Nuvem Nine Consulting
  • Defined the system architecture, including the API and web application.
  • Defined architecture changes to make the system support multiple languages.
  • Designed the architecture to upgrade from RavenDB 3 to 4.
  • Designed architecture to change the queue system from MSMQ to Rabbit MQ.
  • Converted a Vanilla JS application to TypeScript.
Technologies: React, Node.js, JavaScript, .NET, TypeScript, Full-stack, Jest, Test-driven Development (TDD), SQL, Scrum, HTML5, CSS3, Linux, NoSQL

Software Architect

2015 - 2018
Tradehelm
  • Led and implemented the Tele Insurance IVR application project.
  • Contributed to the architecture team defining the microservices ecosystem and web applications.
  • Trained the team in important concepts like TDD, BDD, and DDD.
  • Built a JavaScript framework designed to support front- and back-end validations.
  • Architected tests for the project, including unit, integration, repository, contract, and automated UI tests.
Technologies: React, Node.js, JavaScript, .NET, HIPAA Compliance, Full-stack, API Integration, Jest, Test-driven Development (TDD), SQL, Scrum, HTML5, CSS3

Software Engineer

2014 - 2015
MercadoLibre
  • Developed and maintained the payments subsystem, one of the site's core features.
  • Provided the option to split the payment into two different payment methods.
  • Introduced automated test techniques into the project.
Technologies: JavaScript, Full-stack, Jest, Test-driven Development (TDD), SQL, Scrum, HTML5, CSS3

Architect | Full-stack Developer

2011 - 2014
BVision
  • Consulted on architecture to design new software to achieve higher maintainability and performance.
  • Led the local team for the Dynamic Signal US startup project.
  • Configured continuous integration using TeamCity.
  • Proved uncoupled design portability when the client decided to change the DB provider to be used near the end of the project. The problem was solved in less than a week.
  • Defined architectural standards for new .NET projects in the company.
Technologies: Node.js, JavaScript, .NET, CSS, PostgreSQL, MySQL, Full-stack, Test-driven Development (TDD), SQL, Scrum, HTML5, CSS3

.NET Consultant | System Analysis Pro

2008 - 2011
Verizon
  • Developed mobile applications for laptops and handheld devices to assist technicians with their work.
  • Created a web map aid in order to manage technicians' work areas, making its maintenance and visualization more intuitive.
  • Designed a common rule manager to keep consistency among mobile and centralized applications. Quality, consistency, and cohesion of the code were achieved.
  • Designed and implemented an ORM framework to automate query generation.
  • Built an auto-dispatch engine, which reduced manual dispatch to 25%.
Technologies: ASP.NET, C#, JavaScript, Microsoft SQL Server, Full-stack, .NET, Test-driven Development (TDD), SQL, Scrum, HTML5, CSS3, Oracle

Development Lead | Architect

2007 - 2008
Ypf
  • Developed a JavaScript validation toolkit that parsed MVC validations to automatically generate the equivalent JavaScript ones.
  • Improved the performance of the "Imagen Corporativa" System, fixing database indexes, relations, queries, and hibernate maps.
  • Built an internationalization framework, allowing web apps to be displayed in different languages using a simple configuration process.
  • Monitored the batch tasks engine using web services with a hot plug of new components.
  • Advised other project leaders on technical matters.
Technologies: ASP.NET, C#, JavaScript, jQuery, CSS, Microsoft SQL Server, Full-stack, .NET, SQL

Analyst and Developer

2006 - 2007
Cubika
  • Implemented the remote functionality to support access to remote objects.
  • Developed the dashboard application with the Infragistics components that enabled quick access to problems for technicians.
  • Enabled SQL queries performance enhancements to make queries run in less than a second.
Technologies: ASP.NET, C#, Microsoft SQL Server, Full-stack, SQL, Oracle

.NET Developer

2003 - 2006
SouthWorks
  • Designed a database migration from the old system to the new one.
  • Contributed to the website design for the landing page and dashboard.
  • Handled the migration design from the older .NET 1.1 to Framework 2.0.
Technologies: ASP.NET, Microsoft SQL Server, HTML, CSS, Full-stack, SQL, C++, C

Experience

Resource Manager

Acted as a consultant and senior developer and designed, developed, and maintained the Resource Manager suite of products, including web, desktop, and mobile applications. I coordinated resources in the process of developing new requirements as well as designing the solution for them. I also created and developed toolkits and frameworks.

The primary purpose of the Resource Manager is to dispatch technicians to solve client issues and Verizon network problems.

Serbiznet

Architecture consultant.

Serbiznet is a worldwide client whose business is related to the installation, consulting, layout design, maintenance, etc., of service stations for fuel. My responsibilities include the assessment, improvement of the current system architectures, and designing and developing the new systems.

CompData

CompData provides lawyers in California a platform to interact with the Department of Industrial Relations. The project aims to implement a new web application to replace the current desktop client. The technology stack includes a React application running in Node.js and an API based on GraphQL running in Node.js.

La Postiva Seguros

Built a website for a client based on MVC 4, JavaScript, and .NET Framework 4.5. The project's main goal was to maintain the lifecycle of claims related to health care. The team was composed of two developers, one business analyst, and one tester.

Flow

ROLE: Developer.

A CMS website is based on providing advertising services. Two sites were maintained, including the user portal and manager portal.

The technologies used include Node.js, MongoDB, and Keystone.js. Unit tests ensured quality.

Disney Brief

Architect and senior developer.

A website was built to provide a way of handling documents to design and define products and campaigns for the Disney Company. Different approaches were applied to get the best quality (unit testing, integrations, UI tests, repository, and service patterns), all handled using continuous integration (TeamCity).

Dynamic Signal

https://dynamicsignal.com/
ROLE: Technical leader and senior developer.

An offshore company in San Francisco hired a Buenos Aires team to help develop this application. This application is a marketing platform that uses different social networks (Twitter, Facebook, Tumbler, Blogger, YouTube, etc.) to provide word-of-mouth marketing.

Pharos Innovations

Pharos is a company located in Chicago dedicated to providing healthcare engagement programs to patients with chronic conditions. These programs help them take care of their health and save on expenses.

The old platform was redesigned. The system's architecture includes at least seven REST APIs that talk to each other and provide services to React web applications, IVR systems, and native phone apps.

To obtain the highest levels of quality, the system is implemented using many stacks of automated tests, including unit, integration, repository, contract, integration between APIs, and load and automated UI tests, to quote a few.

Techniques applied to the development process include TDD, DDD, dependency injection, and design patterns. The deployment is automated using Jenkins as a continuous integration platform.

Some other miscellaneous examples of used tools are:
• Sonar for static analysis of code quality
• Stackify to track the website's performance
• Bugsnag to track the website's errors
• RabbitMQ as a queue services platform
• Node.js website using ES6, Webpack, Jest, and SCSS

Bettween

Bettween is a website that pulls tweets from Twitter to discover conversations between users plus other functionalities.

Enhanced the existing website's performance, redesigned its architecture, and significantly improved response time.

CME Group

The current project goal is to create a front-end to make information about the volatility of stocks available to financial consultants of CME. My responsibilities include architecture and leading the implementation of a new SPA based on Node.js and React supported by a set of microservices based on .NET.
The architecture definition includes different layers of automated tests, including unit, integration, etc., and the front-end tests, including unit and component tests.

CME Volatility Project

The current project goal is to create a front end to make information about the volatility of stocks available to financial consultants of CME. My responsibilities include the architecture and implementation of a new SPA (based on Node.js and React) supported by a set of microservices (based on .NET).
The architecture definition includes different layers of automated tests (unit, integration, etc.) and front-end tests, including unit and component tests.

Gateway

https://www.gatewaypetmemorial.com/
Gateway is a pet aftercare company. The system manages the complete cremation process, letting the pet owner choose different services and products, and is composed of three other websites and two mobile apps.

The technology stack includes a React front end, .NET Core REST API, Xamarin, and a RavenDB document database.

AMI Attachments

http://www.amiattachments.com/
AMI is a company that sells attachments for excavators, loaders, etc. The process of quoting and creating orders is currently made by hand. A new web system is being designed and implemented to make this process online. The technology stack includes a React front-end, .NET REST API, and a RavenDB document database

SnowOwl Project

SnowOwl is a network traffic management platform that monitors, routes, and transforms all network traffic to your domains. Or, in simpler terms, it makes it simple and quick to run the DevOps yourself.

The product is currently in the development phase targeting an Alpha version very soon. The web application is implemented in Svelte using Svelte Kit with Material UI components.

While helping to finish the Alpha version, I'm responsible for the Beta phase implemented in React. The new stack is a Next.js app using TypeScript and Tailwind components.

Technologies used include different Cloudflare technologies (Pages, Workers, KV, etc.), Fauna DB, and AWS.

InterviewStream Project

https://interviewstream.com/
InterviewStream is an online platform with tools targeted to simplify the hiring process.

The platform is a monolith with a complicated architecture, suffering from performance issues, and many of the tools have been disconnected from each other. The current goal is to reimagine and modernize the product, integrate all the tools, deprecate the features that are not in use or are not relevant, and create the right product correctly.

The new architecture design includes a set of microservices developed using Python, which is implemented as REST or GraphQL services. The front-end design is a set of micro front ends developed using- React/TypeScript.

The platform runs Docker containers orchestrated by Kubernetes and is hosted in AWS. Datadog and errors by Bugsnag track performance.

Continuous integration is enforced by unit, DB, integration (feature API tests), contract, and UI functional tests. UI components are tested as well.

Using trunk-based development, minimal incremental features are deployed by the end of each sprint, and bigger and more complex features are enabled using feature toggles.

Axis Project

Axis is an application targeted to help the construction industry to plan and execute their projects. It helps industries find the right resources while managing payments, contractors, and third-party companies.

As part of a re-branding strategy, the outdated web applications are being re-architected to target a React SPA application implemented with React, MUI, TypeScript, and Node.js.

Tatango

https://www.tatango.com/
Tatango is America's top political SMS marketing software.

As a development lead, I made technical decisions and interacted with businesses to define requirements and create user stories. I conducted different scrum ceremonies, guided and mentored the team, unblocked problems, and managed the sprint board.

Further, I participated in the architectural design and discussions. Also, I helped businesses achieve their goals by discovering the tools they need and applying continuous integration and incremental feature enhancements.

I used React, Node.js, TypeScript, AWS, and Docker technologies.

Birdseye

Birdseye is a system that enables clients to schedule services on their Volvo cars (on-site and at home), schedule test drives, and schedule new vehicle handover. It provides services to customers, dealerships, and other systems, providing an API so external services interact with it. Users, including clients, dealerships, and technicians, can interact with it through a web interface and mobile applications.

As a staff front-end engineer, I designed, implemented, and led different initiatives, including:
• Feature discovery, design, and implementation
• Performance tuning
• Domain-driven design re-architecture
• Team self-awareness and discovery by implementing auto-regulated retrospective meetings
• Test automation by designing a testing pyramid
• GitHub discussions for feature and technical discussions
• Connected-retail-ui npm UI library

Hirebus

https://hirebus.com/
HireBus is an AI-powered hiring automation platform built for small and medium-sized home services businesses. It combines automated job ads, behavioral science-based candidate scoring (RightSeat™), and AI-driven interview scheduling to reduce time-to-hire and improve long-term retention — giving SMBs access to enterprise-grade recruiting tools.

As the lead architect and engineering coach, I assessed and redesigned the foundational architecture, established development standards, and built a full testing pyramid (unit, integration, and E2E with Playwright). I also introduced contract testing, set up CI/CD on GitHub Actions, refactored the API to follow REST best practices, and coached the team on Agile practices, including backlog refinement, planning, and retrospectives.

Sensible

https://www.sensible.so/
Sensible is a hybrid document extraction platform that combines LLM flexibility with deterministic guardrails—schema enforcement, confidence signals, and full audit trails—making AI-powered document processing production-ready. SOC 2 Type II and HIPAA compliant, used by companies across insurance, real estate, and fintech.

As the back-end and infrastructure owner, I designed and implemented REST APIs following a four-layer architecture, migrated the test suite from Jest to Vitest and E2E from Cypress to Playwright, led the infrastructure migration from SST v2 to SST v3 on pnpm workspaces, and built production systems, including distributed rate limiting, async email processing pipelines, and LLM cost instrumentation across multiple providers.

Education

2010 - 2011

Software Engineering Specialist's Degree in Computer Engineering

Pontificia Universidad Católica Argentina 'Santa María de los Buenos Aires' - Buenos Aires, Argentina

1999 - 2007

Engineer's (Corresponds to a Six-year University Program) Degree in Information Systems

University of Buenos Aires - Buenos Aires, Argentina

Certifications

DECEMBER 2014 - PRESENT

MongoDB for Node.js Developers

MongoDB

Skills

Libraries/APIs

React, jQuery, Node.js, Playwright

Tools

RabbitMQ, Bugsnag, Amazon Simple Notification Service (SNS), Amazon Simple Queue Service (SQS)

Languages

CSS, HTML, HTML5, CSS3, SQL, JavaScript, C#, TypeScript, GraphQL, C, C++, Python, PHP

Frameworks

.NET, ASP.NET, Next.js, Jest, SST, Express.js, .NET Core

Paradigms

REST, Continuous Integration (CI), Unit Testing, Scrum, Dependency Injection, Test-driven Development (TDD), Microservices, HIPAA Compliance

Platforms

Linux, Oracle, Docker, Amazon Web Services (AWS), AWS Lambda

Storage

Microsoft SQL Server, PostgreSQL, Redis, NoSQL, MySQL, MongoDB, Datadog, Amazon DynamoDB

Other

APIs, Full-stack, Serverless, API Integration, Cloudflare, Large Language Models (LLMs), Artificial Intelligence (AI), Prompt Engineering, GitHub Actions, Storybook

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