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donggeonlee

Donggeon L

@donggeonlee

Senior Go Backend Engineer, Payments and Blockchain

South Korea
English, Korean
About me
Senior Backend Engineer (Go, Python) with 15+ years of experience, 8 in Go. I build payment systems (card payments, subscription billing, on-chain USDC) and blockchain services on Ethereum, Hyperledger Fabric, and Cosmos SDK, from backend design to mainnet launch. Stack: Go, Python, Node.js, gRPC, Kubernetes, AWS, GCP, MySQL, ClickHouse, Stripe, PayPal, Authorize.Net, Solidity. 6 years of remote work with teams in the US, Sweden, Israel, and China. Message me before ordering to discuss your project.... Read more

Skills

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donggeonlee
Donggeon L
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See my services

API & Integrations
I will develop a go backend API with payment integration
From$50 / projectMore details
Decentralized Applications (dApps)
I will build defi and blockchain backends, smart contracts and web3 integrations
From$50 / projectMore details

Portfolio

Work experience

WildfireART

Blockchain Developer

WildfireART • Freelance

Jun 2025 - Dec 2025 • 6 mos

• Took over a non-operational blockchain service and resolved critical issues across the Node.js and EVM stack, including Ethereum, Base, and USDC transaction integrations. • Fixed critical bugs in Solidity smart contracts and refactored and optimized them, reducing gas costs and bringing contract size under the EIP-170 (24KB) deployment limit. • Maintained the frontend’s Web3.js integration to keep it in sync with backend and smart contract changes. • Redesigned the system architecture to align with the original product requirements and completed preparations for mainnet launch.

Home_- Bnei Baruch Kabbalah Academy

Back End Developer

Home - Bnei Baruch Kabbalah Academy • Freelance

Jul 2022 - Jul 2024 • 2 yrs

• Maintained Go microservices for event and broadcast registration, orders and payments (Pelecard), and user profiles synced with Keycloak. • Built a lecture subtitles and slides service in Go with Keycloak OIDC authentication and document ingestion from a media archive. • Built Python automation that bulk-downloads Zoom recordings across account users via Server-to-Server OAuth. • Deployed services with Docker and GitLab CI, with automated staging and manual production releases. • Developed the initial frontend, implementing core pages and user flows.

VegaX

Backend / Blockchain Developer

VegaX • Full-time

Feb 2021 - Aug 2022 • 1 yr 6 mos

• Led the Konstellation (DARC) Cosmos SDK chain from mid-development to mainnet launch, including mainnet genesis and network configuration. • Built custom Cosmos SDK modules for an exchange-rate oracle and token issuance, and upgraded the chain’s Cosmos SDK with IBC and CosmWasm support, including IBC connection to Cosmos Hub. • Built a DARC↔BNB Smart Chain token bridge in Go (API, block parser, and worker services) with an order state machine, expiry handling, and automatic retries. • Operated validator and full nodes for the network. • Maintained the oracle price feeder, an explorer REST API with Redis caching, and network tooling for localnet, testnet, and mainnet deployment.