omelianenko

Backend engineer specialising in payment and settlement systems.

For nearly two years I've owned the core payment API at a UAE crypto-to-fiat OTC platform - 90+ REST endpoints, a 38-table PostgreSQL schema, ten async workers and five external money rails, in production and settling real volume.

Most of the work comes down to one problem: making concurrent money operations correct. Exactly-once payouts with idempotency keys enforced at the database level. PostgreSQL advisory locks with conditional-UPDATE guards serialising concurrent balance mutations. A ten-pass ledger reconciliation engine that self-heals missing entries every cycle. Root-causing production money-loss paths that only surface under concurrency or partial provider failure.

Integrations: MPC custody over gRPC, fiat payout rails, bank webhooks, FX providers. Signed outbound webhooks with HMAC-SHA256, SSRF allowlisting and a staged retry ladder.

Looking for: Backend Engineer or Senior Backend Engineer, remote. Payments, custody or exchange infrastructure preferred.

Stack: Python, FastAPI, Pydantic, asyncio, PostgreSQL (raw SQL, hand-written migrations), Redis Streams, Docker, gRPC/protobuf, pytest.