Alex Chen's Portfolio
Selected Works
View all →Payment Retry Engine
Distributed retry system for failed payments using Kafka-based event queuing with per-merchant partition keys, exponential backoff with jitter, and circuit breakers. Handles 2M+ daily retry attempts with 99.1% recovery rate.
GraphQL Storefront API
Unified GraphQL API layer aggregating 12 microservices into a single schema for merchant storefronts. Adopted by 120k+ merchants with sub-50ms P95 latency at 500k RPM peak load.
Real-Time SMS Pipeline
Event-driven Kafka pipeline replacing a polling-based worker for 80M+ daily SMS messages. Improved delivery SLA from 94% to 99.7% and cut median latency from 4.2s to 340ms.
ActiveCache Ruby Gem
Open-source multi-layer caching abstraction for Ruby/Rails with transparent L1/L2 lookups, automatic TTL management, and safe degradation. 1,200+ GitHub stars, 50+ production adopters.
Developer CLI Toolkit
Command-line tool for scaffolding, deploying, and monitoring serverless functions across AWS Lambda and CloudFlare Workers. Built with Go for single-binary distribution.
Hi, I'm Alex.
Senior full-stack engineer with 10+ years building scalable web applications and payment infrastructure. I care deeply about system reliability, developer experience, and clean APIs that teams actually enjoy working with.
📍 San Francisco, CA
Skills & Expertise
Technologies and tools I work with.
Work Experience
Lead Software Engineer
Stripe
Leading a team of 6 engineers on payment infrastructure, responsible for the retry logic and fault-tolerance systems handling $1B+ in daily transactions. Architected migration from monolith to event-driven microservices, reducing P99 latency by 40%.
Senior Software Engineer
Shopify
Built and maintained core checkout services handling 500k+ requests per minute during peak BFCM events. Introduced a GraphQL storefront API adopted by 120k+ merchants, and led the team through 3 Black Friday launches with zero downtime.
Software Engineer
Twilio
Developed real-time messaging and SMS delivery pipeline using Ruby on Rails and Kafka. Improved message delivery reliability from 94% to 99.7% SLA. Built internal developer tooling used daily by 80+ engineers across the platform team.
Software Developer
Thoughtworks
Consultant developer embedded with enterprise clients in banking and healthcare verticals, delivering agile software projects. Championed test-driven development and pair programming. Mentored junior developers across 4 client engagements.
Education
University of California, Berkeley
Bachelor of Science in Computer Science
Class of 2014
Grade: 3.8 GPA
Case Studies
Scaling Checkout for Black Friday
Shopify's checkout infrastructure wasn't built for 10x BFCM spikes. I designed a caching and queue-based session architecture that processed 6.3 million checkouts in 24 hours with zero downtime — a 40% year-over-year increase.
Rebuilding Payment Retry Logic at Scale
Stripe's retry logic for failed payments was a monolithic system causing cascading failures under peak load. I led the redesign into an event-driven retry service — reducing failed payment recovery time by 60% and eliminating 3 recurring production incidents per month.
Real-time SMS Notification Platform
Rebuilt Twilio's internal notification delivery pipeline from a polling-based architecture to an event-driven Kafka system — lifting the delivery SLA from 94% to 99.7% and slashing median latency from 4.2 seconds to 340ms.
Open Source: ActiveCache Ruby Gem
Built and published an open-source multi-layer caching abstraction for Ruby/Rails that has accumulated 1,200+ GitHub stars and is used in production by 50+ companies.