Carlos Kozuszko, Developer in San Miguel de Tucumán, Argentina

Carlos Kozuszko

Back-end Developer

San Miguel de Tucumán, Argentina
Toptal Member Since
October 24, 2016

Carlos has a strong technical background focused on web technologies. He has mastered Ruby on Rails, among other tools, but his focus is on background implementations. For over ten years, he has been managing a web development team as its technical lead and a developer.

Carlos is available for hire
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GraphQL, Ruby on Rails (RoR)
Toptal Client
Ruby on Rails (RoR)
Insignia SRL
JavaScript, Sinatra, Ruby on Rails (RoR), Ruby, Leadership


Ruby on Rails (RoR) - 10 yearsPerformance Optimization - 10 yearsAmazon Web Services (AWS) - 10 yearsLeadership - 10 yearsDatabase Caching - 10 yearsScalability - 8 yearsMongoid - 5 yearsJavaScript - 5 years


San Miguel de Tucumán, Argentina



Preferred Environment

Cloud66, Heroku, GitHub, Git, Ruby on Rails (RoR)

The most amazing...

...websites I've made performance improvements on were required to handle millions of visitors a month.

Work Experience

2019 - PRESENT

API Developer

  • Implemented GraphQL queries and mutations to migrate away from the current REST API implementation.
  • Upgraded the app to Ruby on Rails 6.
  • Improved overall performance on the test suite.
  • Supported and maintained a REST API.
  • Contributed to several database migration endeavors: Enforced overall referential constraints at the database level, improving a data migration framework.
Technologies: GraphQL, Ruby on Rails (RoR)
2018 - 2019

Lead Developer

Toptal Client
  • Developed a Ruby on Rails API.
  • Supervised the work of a 10+ person team doing back- and front-end work.
  • Reviewed code (using GitHub) of all code submitted to the repository. Recommended best practices to other team members and oversaw architectural changes.
Technologies: Ruby on Rails (RoR)
2006 - 2019

Managing Partner/Senior Developer

Insignia SRL
  • Directed technical projects on Ruby on Rails applications. Scaled web apps to handle heavy traffic.
  • Managed a team of developers. Provided technical consulting to the team and handled technical decisions for the applications.
  • Handled tech interviews, evaluating the skills of potential new hires, both hard and soft.
  • Performed code reviews on other people's code. Accepted code requests and assessed the quality of the code.
Technologies: JavaScript, Sinatra, Ruby on Rails (RoR), Ruby, Leadership
2017 - 2018

Lead Back-end Developer

  • Implemented an automated test suite to cover the majority of the codebase which was originally not tested.
  • Integrated third-party services fetching data from multiple sources to our platform.
  • Implemented a GraphQL API to expose information to the front end.
Technologies: Ruby on Rails (RoR), Ruby
2016 - 2017

Back-end Developer

Aces TSS
  • Connected Google Cloud Storage accounts with the application.
  • Set up and implemented a business intelligence platform (Sisense).
  • Used CloudWatch to gather and report detailed metrics about storage use on AWS.
  • Reviewed code for other team members.
  • Implemented and documented API endpoints with Swagger.
Technologies: Google Cloud, Amazon Web Services (AWS), Ruby on Rails (RoR), Ruby



BoxUp is an eCommerce platform developed to connect small businesses and corporate ERPs and the leading Latin American eCommerce platforms (MercadoLibre and TiendaNube).

It's also an email marketing tool allowing sellers to send massive volumes of email to their clients, which are automatically imported from the marketplaces.

I have written all the back-end code for this project in Ruby on Rails for the past two years. It currently uses Rails 4.2 and MongoDB+Mongoid as a database.

It handles background tasks with Resque to connect with external APIs and massive email sending.

Gugu Guru
I'm responsible for the overall architecture, reviewing the code implemented by the development team.

I have personally migrated the project to the latest version of Ruby on Rails (4.2 at the time) and MongoID 5.1

My involvement on MissionHub was on the back-end side, maintaining and adding features to the Ruby on Rails API



JavaScript, Ruby, CoffeeScript, GraphQL, PHP


Ruby on Rails (RoR), Swagger, Sinatra


RSpec, GitLab, GitHub, Basecamp, Cloud66, Git, Amazon CloudWatch, AWS SDK, Bitbucket, Trello


Heroku, New Relic, Amazon Web Services (AWS), Linux, Google Cloud SDK, Amazon EC2, DigitalOcean


Front-end, Scalability, Performance Optimization, Optimization, Ruby on Rails Consulting Specialist, Leadership, WebSockets


Shopify API, Mongoid, jQuery, Vue


Redis, Amazon S3 (AWS S3), Database Caching, PostgreSQL, MongoDB, Memcached, MySQL, Google Cloud, Google Cloud Storage, SQLite


2011 - 2013

Master's Degree in Business Administration

Universidad del Norte San Tomás de Aquino - San Miguel de Tucuman

1999 - 2006

Engineer's Degree in Computer Engineering

Universidad Tecnologica Nacional - Facultad Regional Tucuman - San Miguel de Tucuman