Filip Vavera

Professional Summary

Senior Software Engineer with 12+ years of experience building backend systems and data-heavy products. Since 2018, I have specialized in Elixir/Phoenix, shipping secure, reliable services for analytics and fintech. I am comfortable owning greenfield projects, modernizing legacy systems, and leading small teams in remote environments.

Core strengths

Backend engineering (Elixir/Erlang, Phoenix, OTP) and API design
Data systems and performance (SQL, ClickHouse/PostgreSQL/MySQL, pipelines, background workers)
Security-minded engineering (authentication, MFA, cryptography, secure integrations)
Distributed systems and event-driven architecture (Kafka, CQRS/EventSourcing)
Mentoring and technical leadership (design reviews, planning, delivery)

Work experience

CrazyEgg - Senior Software Engineer

February 2022 - present

https://crazyegg.com/

Lead technical design and implementation of a secure, scalable backend in Elixir for a high-traffic analytics product.
Rewrote a legacy authentication system (multi-factor authentication, secure password reset) while maintaining backwards compatibility and improving developer experience.
Built and optimized background workers and SQL queries for analytics workloads at scale (millions of events/day).
Integrated third-party APIs and built internal tools, improving Customer Success incident response by ~20%.
Prototyping and shipping AI-assisted features and LLM/agent integrations in Elixir.

BnT - Software Architect

May 2020 - December 2020

https://bntlab.com/

Architected and delivered the backend for a gold trading prototype, including payment processors, FX conversion, and transaction validation.
Backend written entirely by me using EventSourcing/CQRS as a core principle.
Collaborated remotely with a small team (backend, mobile, UI) to deliver a Proof of Concept under tight deadlines.

DivvyPay (now BILL Spend & Expense) - Team Leader and Senior Software Engineer

April 2018 - February 2022

https://www.bill.com/product/spend-and-expense

Led a team of 8 engineers in a fast-growing fintech startup, overseeing development of payment processing, bank integrations, credit card issuance, and loan approval systems.
Guided technical strategy and implementation as team lead as the company scaled from ~10 to 250+ engineers.
Pioneered remote work as the only distributed team member, keeping execution tight across time zones.
Built and optimized secure backend services, improving reliability and performance of critical systems.

profiq - from QA to fractional CTO

January 2015 - April 2018

https://profiq.com/

Transitioned from QA automation to full-stack development, working on diverse projects including React.js applications, NodeJS servers and real-time Django servers.
Developed early virtual reality applications and plugins, demonstrating adaptability to emerging technologies.
Served as partial CTO for Serenity, leading technical strategy and implementation for client projects.

Open Source

Domainatrex

Elixir library for parsing TLDs from URLs using the Public Suffix List. I took over maintenance from Zen and have completely rewritten it so it is more performant and correctly handles edge cases.

secp256k1

Elixir NIF library wrapping Bitcoin’s secp256k1 C library, used for cryptographic operations.

Noise Protocol

Elixir implementation of the Noise Protocol, an alternative to TCP/SSL with configurable encryption options.

Nostr Libraries

Collection of Elixir projects implementing Nostr protocol specs, focused on distributed systems.

SpaceBoy

Elixir library for the Gemini Protocol, a lightweight alternative to HTTP.

Elixir Astro

Elixir library wrapping NASA SPICE library and ERFA library, enabling advanced computational integrations.

Technical Skills

Languages: Elixir, SQL, Python, TypeScript
Frameworks: Phoenix, Phoenix LiveView, Ruby on Rails (maintenance)
Data: ClickHouse, PostgreSQL, MySQL, Redis, Kafka
Cloud/Infra: AWS, Google Cloud, Docker, Kubernetes, CI/CD
Observability: Grafana, Prometheus
Security: authentication/authorization, MFA, cryptography, OAuth