Sergio Andres Köller Vargas, Software Developer in Cochabamba, Cochabamba Department, Bolivia
Sergio Andres Köller Vargas

Software Developer in Cochabamba, Cochabamba Department, Bolivia

Member since December 18, 2019
Sergio is a developer with an entrepreneurial soul who's passionate about creating amazing, new products while building strong working relationships with his colleagues. For the last five years, Sergio has been working as a full-stack developer in Bolivia, the United States, and Europe.
Sergio is now available for hire




Cochabamba, Cochabamba Department, Bolivia



Preferred Environment

Google, GitLab, Slack, Ubuntu

The most amazing...

...project I've worked on is a blockchain-based voting system that was considered for the electoral process of Bolivian state companies.


  • Senior Full-stack Developer

    2017 - PRESENT
    • Developed a full-stack (internal) system for tracking the weekly progress of team members and teams.
    • Designed and implemented an architecture for Ruby on Rails APIs abstracting the controller logic into commands (based on the command-driven architecture).
    • Built an API for abstracting the payments of different gateways (Stripe, Dwolla, etc).
    • Implemented Ruby on Rails API wrappers for Oracle database stored procedures.
    • Updated legacy Rails projects to work on Rails 5 and Ruby 2.3.
    Technologies: Oracle Database, React, Ruby on Rails (RoR)
  • Senior Full-stack Developer

    2018 - 2019
    Creator Mobile
    • Developed an app to help apartment buyers monitor the construction of their new apartments, managing payment plans, and accommodation.
    • Built a web-and-mobile-based app for a Bolivian social network centered around family life; this includes connecting with nursing homes, schools, and daycares. This system is being launched in Cochabamba, Bolivia.
    • Implemented the back end (using cloud functions) for a hotel management system.
    • Developed an app for the Scusa restaurant in Santa Cruz, Bolivia. The app reflects the restaurant's experience of homemade dinners.
    Technologies: Firebase, React Native, React
  • Senior Full-stack Developer

    2016 - 2018
    Freelance Work
    • Implemented a web app (full-stack) for peer-review that is being used in some classes in ETH Zurich, MIT, and others.
    • Developed a set of apps for food orders, deliveries, and restaurant management for a food delivery project.
    • Built an MVP for automatic cryptocurrencies trading using the binance API and technical analysis.
    • Maintained more than 20 web-based systems in Digital Ocean servers.
    • Automated the recollection of more than 10,000 job offers in Mexico DF for future data analysis.
    • Developed informational websites for more than ten businesses in Bolivia.
    • Implemented a system to track the traffic in and out of stores. This involved implementing the sensors, NodemMCU, back end, and a web app. This system is used in more than 50 stores around Bolivia.
    Technologies: Laravel, Watir, Apache, NGINX, PostgreSQL, React, Ruby on Rails (RoR)


  • Voting System Based on Blockchain Technology

    I designed a big scale voting system based on blockchain technology and the bitcoin infrastructure. I validated this design with a prototype used for my student body university elections. We published this and the results in the Actanova magazine.

    Technologies: Multichain, Ruby on Rails, PostgreSQL

  • DVSN: Peer-review System

    I developed a peer-review system MVP. The project was implemented using the mechanism presented in the article "impartial division of a dollar" by Geoffroy De Clippel and was led by Heinrich Nax. The system was developed under the guidelines of the project owner.

    Technologies: Ruby on Rails, PostgreSQL, Bootstrap

  • Scusa App

    I developed an app for the Scusa restaurant in Santa Cruz, Bolivia. This restaurant focuses on creating memorable moments through a game for couples and groups to make a customized restaurant experience. The app is used to recreate that restaurant's experience while at home.

    Technologies: React Native

  • TRIII | Efficient Family Apartments

    This app helps apartment buyers monitor the construction of their new apartments. This includes live streaming of the construction site, managing payments, and organize accommodations (e.g., who owns what garage).

    Technologies: React Native, Firebase

  • Informational Website for the Architect Raul Maclean

    I developed and designed an informational website for architect Raul Maclean using the Laravel and Bootstrap frameworks. It has a back-end service to manage all the displayed information using the guidelines for image and text sizes.

    Technologies: Laravel, PostreSQL, Boostrap

  • Cryptocurrency Trader

    This is an open-source project implementing a cryptocurrency trader. This trader uses a combination of well-known trading algorithms (Williams R, RSI, and EMA) to see when is the best time to perform a trade. We have only used this trader in simulation mode, which starts with a set amount of investment dollars and runs fully automated performing simulated trades.

    Technologies: Laravel, Binance API


  • Frameworks

    Ruby on Rails (RoR), React Native, Material UI, Laravel, Laravel 5
  • Libraries/APIs

    React, React Redux
  • Languages

    Ruby, JavaScript, C++
  • Platforms

    Ubuntu, Firebase, DigitalOcean, Linux, Oracle Database, MultiChain
  • Other

    Web MVC, Web Development, Google
  • Tools

    GitLab, NGINX, Apache, Watir, Git, Slack, RSpec
  • Paradigms

    REST, Agile, Test-driven Development (TDD)
  • Storage

    JSON, PostgreSQL


  • Bachelor's Degree in Systems Engineering
    2011 - 2016
    Universidad Católica Boliviana "San Pablo" - La Paz, Bolivia

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