Donggeon L.

Clients usually bring me in when a backend is stuck, breaking, or too tangled to change: monoliths that need splitting, payment flows that keep failing, or projects left half-done. I'm a senior backend engineer with 15+ years of experience building and maintaining production systems using Go, Python, and Node.js. I work on both new backend development and existing systems that need fixing, scaling, or restructuring. I've worked remotely for 6+ years. Selected work - Took over a non-working blockchain service and got it to production, fixing the Ethereum, Base and USDC transaction integrations that had blocked deployment. - Stopped webhooks from corrupting subscription data in a legacy Stripe/PayPal billing system by verifying each event against the provider's API before writing to the database. - Led legacy migrations across several companies: split a monolithic Go server into microservices on GCP, moved legacy PHP servers to Go, worked on a Laravel-to-Go migration, and migrated services from Spanner to MySQL. - Launched a blockchain credit data service on Ethereum and Hyperledger Fabric, and later built Cosmos SDK services and token swap backends. - Built real-time messaging backends, including a chat system with Redis Pub/Sub and SSE that handles long-lived client sessions. Backend: Go, Python, Node.js, gRPC, REST APIs, microservices, distributed systems Payments: Stripe, PayPal, Authorize.net, Heartland, subscriptions, billing, tax Blockchain: Ethereum/EVM, Solidity, Cosmos SDK, Hyperledger Fabric, wallets, token swaps Data & infrastructure: MySQL, Spanner, ClickHouse, Redis, MongoDB, Pub/Sub, Docker, GCP, AWS Worked with teams in the US, Europe, Israel and China. Can start right away.