Vasilis Sakkas

Senior Backend Engineer

I build and own high-traffic backend systems in production.

NestJS · PostgreSQL · TypeScript

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Based in Thessaloniki, Greece — relocating to the Netherlands in the next 2 months.

Case Studies

InstaPOS Platform Rewrite

Context

  • Legacy POS platform under heavy operational load.
  • Technical debt limited performance, reliability, and extensibility.
  • Rewrite required without disrupting daily operations.

Role

  • Backend engineer on the core rewrite team for nearly a year.
  • Worked on backend architecture, domain modeling, and critical service flows.

Key decisions

  • Improved service boundaries and maintainability with a structured NestJS architecture.
  • Designed PostgreSQL models for transactional consistency and operational queries.
  • Supported gradual migration and risk-controlled rollout.
  • Prioritized reliability and observability for safe production operation.

Outcome

  • More robust architecture and a cleaner foundation for ongoing development.
  • Improved stability and performance under real production load.

Multi-Channel WebSocket Communication System

Context

  • Operational teams needed reliable real-time coordination.
  • Existing solutions were difficult to extend beyond a single use case.

Role

  • Designed and implemented a multi-channel WebSocket system from scratch.

Key decisions

  • Used WebSockets to meet real-time requirements efficiently.
  • Isolated channels to support independent communication flows.
  • Handled reconnection and fault scenarios for unstable networks.
  • Built it to be extensible beyond chat.

Outcome

  • Enabled reliable real-time coordination across operational teams.
  • Reusable base for additional real-time capabilities.

About

I'm a backend engineer with 10+ years of programming experience and 3+ years working on production-critical systems at InstaShop. I focus on system design, reliability, and building software that stays maintainable as complexity grows. I value clear communication, pragmatic engineering, and shared ownership within teams.

Contact

Email: vasilis@sakkas.me

Based in Thessaloniki, Greece — relocating to the Netherlands in 1–3 months upon job offer.

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