Alex Chen

Lead full stack development for core platform serving 5M+ monthly active users. Architect distributed systems and mentor team of 6 engineers. Drive adoption of AI-assisted development workflows using Claude Code and GitHub Copilot to accelerate feature delivery and improve code quality.

Real-Time Collaboration Platform

• Built a real-time collaborative document editing platform with conflict-free replicated data types (CRDTs), supporting 50,000 concurrent users with sub-100ms latency.
• Microservices on AWS EKS, WebSocket clusters with Redis pub/sub, PostgreSQL with logical replication, event sourcing with Apache Kafka
• Led architecture design, implemented core synchronization engine, established CI/CD pipelines, and integrated observability with OpenTelemetry and Grafana
• Tech Stack: TypeScript React Node.js PostgreSQL Redis Kafka Kubernetes WebSockets CRDTs
• Challenges: AI-Assisted Feature Development: Used Claude Code for task decomposition and repository-context exploration to implement complex CRDT merge algorithms. Human-supervised workflow included local validation, peer code review, and automated regression testing. Reduced implementation time by 40% while maintaining zero production bugs.
• Challenges: Performance Optimization: Achieved 99.9th percentile latency under 100ms through intelligent operation batching, connection pooling, and CDN edge caching. Implemented model routing with fallback strategies for AI-assisted code generation tools.

Intelligent Search and Discovery System

• Developed hybrid search platform combining full-text, semantic, and structured queries with automated reranking and citation-quality scoring.
• Python/FastAPI services, Elasticsearch, custom reranking service, S3 for evaluation datasets, MLflow for model versioning
• Designed search pipeline architecture, implemented hybrid retrieval with custom reranking, built evaluation framework with regression testing
• Tech Stack: Python FastAPI Elasticsearch PostgreSQL Docker AWS Lambda MLflow
• Challenges: Hybrid Retrieval Architecture: Implemented structured output constraints for query parsing, enabling precise filtering alongside semantic search. Built context quality metrics and tracing with OpenTelemetry for observability.
• Challenges: Evaluation and Regression Testing: Created evaluation datasets with labeled relevance judgments. Automated regression testing in CI to prevent ranking degradation on model updates, achieving 15% improvement in NDCG@10.

Developed customer-facing web applications and internal tools for a rapidly growing SaaS company. Collaborated with product and design teams to deliver features on time. Introduced TypeScript and automated testing practices to improve code reliability.

Subscription Billing Platform

• Built multi-currency subscription management system with complex pricing rules, invoicing, and payment reconciliation.
• Node.js/Express monolith, PostgreSQL, Stripe API integration, React frontend, Docker containers on AWS ECS
• Implemented billing engine core logic, payment webhook handlers, invoice generation, and admin dashboard for finance operations
• Tech Stack: Node.js Express React PostgreSQL Stripe API Docker AWS ECS Jest
• Challenges: Payment Reliability Engineering: Designed idempotent webhook processing with exponential backoff and dead-letter queues. Reduced payment processing failures by 85% and eliminated duplicate charge incidents.
• Challenges: GitHub Copilot Integration: Piloted GitHub Copilot for test generation and documentation updates. Established team guidelines for human review of AI-generated code, including security/permission review and rollback readiness. Improved unit test coverage from 45% to 78%.