Denis S.

Architect, Tech Lead | FinTech, Trading, iGaming | Go, Python, AI

Writing code is no longer the bottleneck. Judgment is: knowing what to build, how to structure it, and what breaks under real load. That is what I sell, backed by 12+ years across architecture, backend, full-stack and infrastructure. 17,000+ hours on Upwork, 100% Job Success, Top Rated. AI made me faster, not different. I use it the way a senior engineer should: to compress the work, while architecture, trade-offs and production decisions stay mine. That combination means one experienced engineer can now take a product from an empty repository to something real, shipped and running, and keep it alive under real traffic and real money. 5,000+ concurrent users at 1,000+ RPS, payment gateways, provider integrations, live multiplayer. Twelve years in fintech and iGaming, domains that punish you for getting it wrong. WHAT I TAKE ON - Zero to product: discovery, architecture, build, deploy, monitoring, end to end, solo or leading a team - Rescue and scale: inherited codebases, performance problems, systems buckling under growth - The hard parts: payments, real-time, integrations, AI features, infrastructure HIGH-LOAD, REAL-TIME & TRADING SYSTEMS - Low-latency services, real-time feeds, WebSocket streaming, event-driven pipelines - Market data handling: ingestion, OHLCV and tick storage, time-series databases - Exchange, broker and liquidity-provider integrations; execution and order plumbing - Backtesting and strategy-runner infrastructure, charting backends, trading dashboards - Scalable transaction processing: payments, wallets, ledgers, idempotency, reconciliation - I am the engineer, not the quant. You bring the strategy or the model, I make it run reliably in production. BACKEND & APIs - Go, Python, Java, Kotlin, TypeScript, C - REST, gRPC, GraphQL, WebSockets, OpenAPI - Microservices, event-driven architecture, high-load and real-time services FULL-STACK & PRODUCT - React, Next.js, Node.js and TypeScript front ends on top of my own APIs - Admin panels, back-office portals, dashboards and trading UIs DATA & INFRASTRUCTURE - PostgreSQL, MySQL, MongoDB, Redis, Elasticsearch, time-series stores - Kafka, RabbitMQ, PubSub - Docker, Kubernetes, Helm, Terraform, AWS, GCP - CI/CD with GitHub Actions and Jenkins, monitoring and observability AI IN REAL PRODUCTS - AI features inside existing products: assistants, semantic search, classification, document processing - RAG and retrieval over your own data - Agents and automation wired into real backends instead of brittle no-code chains - Local and self-hosted models when your data cannot leave your infrastructure - Custom agent tooling for engineering teams; Claude Code is my daily driver DOMAINS - Fintech: payment gateways, BNPL, real-time scoring, neobank infrastructure - iGaming: core platforms, games logic, high-load multiplayer, third-party integrations - Also HR tech, video processing, surveillance, dating and booking platforms TRACK RECORD - 74 contracts, 17,000+ hours, 100% Job Success, Top Rated - Scaled a casino platform to 5,000+ concurrent users at 1,000+ RPS, and migrated it from IBM to AWS - Lead Backend on two iGaming platforms: payments, public API, games logic, CI/CD - Built a B2B credit-card product end-to-end: real-time scoring, risk tooling, public API - Built a neobank QA API and a ClearBank simulator, wired into existing CI/CD pipelines - Co-founded a software company from zero: desktop apps, CLI tools, ML for image recognition HOW I WORK Strong opinions on architecture, held loosely. Simple systems that stay simple as they grow: clear contracts, real observability, infrastructure that holds under load. Direct communication, no surprises, no over-selling. Available part-time for contracts, consulting and short projects. Tell me what you're building.