
Andrei Kaleshka
Verified Expert in Engineering
Software Developer
Warsaw, Poland
Toptal member since September 3, 2013
Andrei is a seasoned web development expert with over 15 years of experience. The open-source software he's developed has been downloaded more than 4 million times worldwide. Although he's worked across a wide range of business domains, billing, payment, and accounting systems remain his primary areas of interest and expertise. Andrei brings strong capabilities in project implementation, management, and long-term maintenance.
Portfolio
Experience
- Ruby - 15 years
- Ruby on Rails (RoR) - 15 years
- React - 10 years
- PostgreSQL - 10 years
- Accounting Systems - 10 years
- Online Classes & MOOCs - 10 years
- Fintech - 10 years
- Billing Systems - 10 years
Preferred Environment
Ruby, PostgreSQL, Fintech, React, Accounting Software
The most amazing...
...fact is that a single open-source library I created has been downloaded nearly 3 million times.
Work Experience
Software Engineer
Palladium Group
- Implemented an API gateway for a third-party team from scratch.
- Improved code in the mission-critical part of the system that reduced bugs the team struggled with for ages, and spent a lot of time on debugging and fixing the data.
- Upgraded stack (Ruby/Rails/PostgreSQL) to current versions.
- Resolved several critical and tricky bugs around the login page and having stock inventory out of sync.
- Designed the architecture for app customization and expansion in global markets.
Founder
WideFix
- Built a strong team of software engineers, capable of delivering high-quality results.
- Created a business strategy and personal branding site from scratch.
- Managed successfully a team of around five software engineers.
- Developed a competitive and cost-efficient financial model.
- Established an effective business model that consistently delivers results.
Senior Back-end Ruby on Rails Engineer
NovoEd
- Replaced a missing team member for the period when the team had a lack of free hands to complete several urgent projects.
- Extended existing functionalities around notifications to students with advanced filters for whom and when to send them.
- Collaborated effectively with the team in the project: QA, CTO, and PM.
- Added two recurring report generators with automatic upload to AWS S3.
Technical Lead Consultant
GRAFO AI LLC
- Analyzed the current state of the development process through interviews with all team members, code review, reading docs, testing the product.
- Streamlined development processes that boost speed and product quality.
- Consulted the business owner on architectural decisions, team performance outcomes, and product evaluation, helping identify a faster and more cost-effective path forward.
- Helped to find the right people for the project who are cost-effective and provide high-quality results.
RoR Developer
Platform 21 Limited
- Unblocked a completely stalled background jobs queue that was holding jobs processing third-party API calls.
- Optimized a DelayedJob queue by redesigning job handling and dispatching, fully eliminating daily performance bottlenecks and queue stalls.
- Improved application performance, eliminating recurring H12 errors on Heroku that previously occurred multiple times per day.
- Added third-party integrations to the system, including Etsy, TikTok, Mailchimp, Awin, and Smiffys.
- Fixed bugs in existing integrations with the system, including Xero, Kashflow, Clearbooks, QuickBooks, and Lightspeed (formerly Vend).
- Added more functionalities to the existing and new integrations.
Senior React/RoR Full-stack Developer
Kajabi, LLC
- Improved page load speed by 80 times. Used SQL to get rid of N+1 issues.
- Added the vendors' directory page from scratch. That improved the app revenue by 100%.
- Resolved several show-stopper bugs within just 1 hour.
- Fixed numerous bugs throughout and implemented pagination, advanced search filters, and full-text search. These enhancements significantly improved the user experience and made the app more user-friendly.
- Implemented several API endpoints for the new pages.
- Introduced an authorization system into the app using a Pundit gem for that.
Music Website Developer
Worship Online Inc.
- Rewrote the entire web version of the application.
- Implemented a custom audio mixer player for the new site.
- Developed a solution that allows moving the clients from the old site to the new one with no risks for the business. New clients grew by 90%, and the business increased its year-over-year revenue by 5% despite the financial crisis.
Senior Software Engineer and Team Leader
Hubstaff
- Led a team responsible for customer support. The team reduced customer support requests two times, and its health metrics (according to office vibe) were above 9.0.
- Brought good habits to the development department that improved application stability and code review quality, and drove an initiative to improve documentation.
- Introduced fundamental design patterns into the code (business action, query object, serializers, etc.) to expedite development and reduce number of defects in the system.
- Implemented back end for events happening in real time used by a live map on the front end.
- Integrated a push notifications system to send real-time messages if users are at an interesting location on time.
- Integrated Zapier so that customers could build their own workflows.
Ruby Consultant
Molinelli Media Group Sl
- Integrated and maintained Stripe payment system to generate invoices and automatically charge clients.
- Changed a single dropdown to multiple dropdown for the main entity in the application.
- Improved speed of page based on PosgreSQL Full Text Search for 99% so that page loads for 300 ms instead of 30 seconds.
- Implemented subscriptions functionality so that clients see what for they pay for and automated money collection is possible.
- Expanded the service location from Spain only to UK + Spain.
Back-end Developer
Toptal
- Integrated and maintained Stripe and PayPal payment systems, Intacct with the billing system, the invoicing system, and the accounting system.
- Refactored a monolithic application so that it's ready for microservice architecture.
- Extracted the billing domain to a separate service.
- Implemented the new API using GQL for the new UI. It was also used for back-to-back communication.
Ruby Developer
GobGob
- Reduced bugs and failures around sophisticated booking rules in a hotel booking project.
- Implemented custom packaging offers for bookings. That feature made the app more price-attractive for end users.
- Made code 10x faster on one project by using SQL techniques instead of Ruby/Rails approaches.
- Prepared the site for users working on the app in parallel by addressing race-condition issues that could corrupt the database.
Team Leader
Mezuka, LLC
- Created a very big application with complex business logic from scratch.
- Built a team of software engineers capable of doing their job efficiently.
- Made decisions on suitable technologies to implement a successful product and to achieve comfortable work for the developers and the product owner.
- Integrated applications with numerous third-party services such as Authorize.net, Twilio, TaxCloud, eFax, and many others.
- Implemented a complex system for displaying zip code areas on a map, enabling full-text search with filters by zip areas, calculating distance between coordinates, and performing other custom matchings and smart geolocation.
- Implemented a single-page application with fully separated back-end and front-end parts.
- Established development processes needed by the company.
- Hiring and overseeing software developers for this project.
Author
Packt
- Wrote a book about Rake, which currently holds an average rating of 5.0 stars on Amazon.
- Wrote the first and only book on Rake, establishing myself as a recognized advocate and evangelist for the tool.
- Created a practical, step-by-step project featured as an example in the book.
Web Developer
Active Cloud
- Built the architecture of a billing system that allowed it to scale the business by adapting to any client with minimum effort.
- Built an RMS system from scratch for cloud resources and related entities.
- Implemented APS package parsing and integrated it with the corresponding resources in the RMS.
- Refactored nearly the entire application, eliminating a large amount of legacy code.
- Improved project architecture by splitting models and controllers into modules (a.k.a. Rails Engines).
Web Developer
Altoros Development
- Supported numerous projects for this company, including Keenprint, AllProShipping, and CrossArts.
- Learned English by taking free English courses provided by the company.
- Took numerous business trips to the US, Norway, and England to meet with customers and project owners.
- Improved the architecture of numerous Altoros projects, allowing for the removal of large amounts of legacy code.
- Integrated a variety of payment systems into projects, including Authorize.Net, PayPal, and more.
- Learned to implement multi-tenancy applications while working on the development of Keenprint.
- Taught students. Read lectures and reviewed code using Gerrit.
Web Developer
Synesis
- Learned the Ext JS framework while creating a project module.
- Learned the SOAP web service protocol while creating a project module.
- Gained direct experience with code reviewing practices.
Network Administrator
BNTU University Dorm #4
- Administrated a server running Debian OS for local network.
- Learned and configured iptables in so way it allowed admins to ban network users on demand.
- Created a local billing system using Rails, which allowed us to track user balance and ban them when it's zero.
- Acquired an extensive understanding of network systems, including DNS, firewalls, and Unix systems.
Software Engineer
BelHard
- Dealt with billing systems and banking system formats.
- Learned Python to be able to edit one of the project modules.
- Extended the current functionality for processing bank transactions via FTP.
Web Developer
360 Media Group
- Worked on 360.by, a project that was already part-way into the production process.
- Observed how poor architecture can negatively impact a project.
- Gained experience with using version control systems.
Experience
WorshipOnline
https://app.worshiponline.com/Compare the new site - https://app.worshiponline.com/ and the old site - https://classic.worshiponline.com/.
Toptal Clients
• Refactored a monolithic application so that it's ready for microservices architecture
• Extracted the billing domain to a separate service
Mezuka
Stack: Ruby, Grape, RESTful API, AngularJS, Cucumber, Rspec, Jasmine, RabbitMQ, PostgreSQL, Design Patterns, Twilio, Rails, Wkhtmltopdf, ImageMagick, Omni Auth, Elasticsearch, E Fax, Merchant Services, Delayed Job, TaxCloud, Amazon S3, Ansible, SSE (Server Sent Events), Google Maps API
ActivePlatform
https://activeplatform.com/Stack: Rails, XML, XPath, PostgreSQL, RSpec, TDD, Scrum, APS.
Blogging
https://widefix.com/blogRake Task Management Essentials
Keenprint
http://keenprint.comStack: Ruby, Rails, Active Merchant, FedEx/UPS/USPS, jQuery, Ajax, RSpec, MySQL.
Fisikal
http://fisikal.comStack: Ruby, Rails, jQuery, Ajax, SMS gateway, RSpec, MySQL.
Ruby Enums Gem
https://github.com/mezuka/enumMigration Data Gem
https://github.com/ka8725/migration_dataI designed and developed this gem on my own to improve our team productivity when we had constant failures during database migrations. It allowed us to save tens of hours in total as a team weekly by preventing the issues with migrations.
As of now, the gem has been downloaded around 3,000,000 times.
Open Source Activity
https://github.com/ka8725ActualDbSchema
https://widefix.com/dbactual_db_schema is a Ruby gem for Rails that ensures your database schema remains consistent when switching between branches during development. It automatically detects and rolls back “phantom” migrations - those that were run in another branch but don’t belong to the current one - preventing errors and eliminating irrelevant diffs in schema.rb or structure.sql. I developed this gem entirely on my own as a unique solution with no analogues.
To date, it has been downloaded around 500,000 times.
Education
Certification in Computer Science
University of California San Diego - San Diego, CA
Bachelor's Degree in Automobile Engineer
Belarussian National Technical University - Minsk, Belarus
Certifications
Microeconomics Principles Specialization
University of Illinois Urbana-Champaign | via Coursera
Basic Statistics
University of Amsterdam | via Coursera
Mathematical Thinking in Computer Science
University of California | via Coursera
Data Structures and Algorithms Specialization
University of California | via Coursera
Skills
Libraries/APIs
Stripe, REST APIs, Stripe API, Stripe Connect, Ruby on Rails API, React, Wistia API, Sidekiq, Node.js
Tools
Shell, Rake, Ansible, RabbitMQ, Cucumber, Watir, RSpec, NGINX, Sublime Text, Zsh, Git, Intacct, Zapier
Languages
JavaScript, Ruby, TypeScript, GraphQL, SQL, HTML, HTML5, CSS3, CSS, Java, Python, CoffeeScript, SCSS, Sass
Frameworks
Ruby on Rails (RoR), Ruby on Rails 5, Next.js, Bootstrap, GrapesJS, Jasmine, Ember.js, AngularJS, Knockout (Knockout.js), Slim
Paradigms
Object-oriented Programming (OOP), Design Patterns, Test-driven Development (TDD), Behavior-driven Development (BDD), Interactive Design, Software Testing, REST
Platforms
Heroku, Amazon Web Services (AWS), Docker, OS X, Music Streaming, Visual Studio Code (VS Code), Vercel
Storage
Elasticsearch, PostgreSQL, Redis, Amazon DynamoDB, Databases
Industry Expertise
Banking & Finance, Accounting, Bioinformatics
Other
SOLID Principles, Payment Gateways, Billing, Billing Software, Billing Systems, Full-stack, API Integration, Fintech, Domain-driven Design (DDD), Accounting Systems, Accounting Software, Web Development, Finance, Online Classes & MOOCs, Server Sent Events (SSE), PayPal, Content Writing, Technical Writing, Music, IT Automation, Problem Solving, Computational Logic, Computer Science, Algorithms, Critical Thinking, Data Structures, Graph Theory, Probability Theory, Data Visualization, Statistics, Market Research, Correlational Analysis, Business Psychology, Cost Accounting, Process Analysis, Behavioral Economics, Heroku Postgres, Programming, Theoretical Computer Science, Computer Programming, Network Analysis, Analysis, Engineering, Mechanics, Printing, Logistics, Exercise & Fitness, Fitness Trackers, Fitness Website Design, Sports, Cloud Computing, Digital Resources, Technical Reviews, Technical Research, Business Development, New Business Development, Branding, Personal Branding, Personal Finance Management, Web Marketing, Publishing, Ebook Writing, Writing & Editing, Integration, APIs, Monitoring, Message Queues, Queue Management, Cars, Code Review, Source Code Review, Artificial Intelligence (AI), Team Leadership
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