Sebastian Sastre

Work Experience

• Software Engineer

  Kraken (Payward, Inc.), May 2024 to Apr 2026
  • Backend engineer on a Rust microservice for user incentives and rewards at a global crypto exchange: enrollment, eligibility, abuse detection, payouts, and programs that drive activation and revenue.
  • Owned many incentives lifecycle features in Rust. Designed a multi-stage state machine serving hundreds of thousands of enrolled users and well over a billion data points. Built fault tolerance and self-healing into the engines so campaigns ran under my end-to-end ownership without production incidents intentionally by design.
  • Rebuilt payment processing as an idempotent event-driven engine. Replaced a table-based implementation with a generic, scalable pipeline that could serve payment sources beyond the original use case, for hundreds of thousands of users.
  • Built an AI-assisted, spec-driven delivery harness with review gates (not ad-hoc prompting). Shipped 10+ production features under that workflow; in one week, delivered four in parallel in the same Rust codebase.
  • Partnered with product, peer engineering teams, and marketing technology on requirements and on downstream consumers of events from owned features.
  Rust, Tokio, Kafka, MariaDB, Event-driven services

• Senior Software Engineer · Roaming Infrastructure

  Telna, Sep 2019 to Aug 2023
  • Core team on the mobile network roaming infrastructure: session management at petabyte scale across the North American market. Owned components held production stability as traffic grew past 1 PB/month.
  • Implemented a Rust caching system that extended main backend capacity past 25K ops/s; learnings and parts of the PoC fed into production work that continued to expand throughput past 1 PB/month.
  • Built a Go multithreaded synthetic-traffic client to validate SLAs and stress-test the backend; it surfaced a virtual-machine issue and helped define safe operating limits per instance.
  Smalltalk, Rust, Go, Python, Docker, TDD

• Full-Stack Engineer · Ad Tech

  Sulvo, May 2017 to Dec 2019
  • Full-stack engineer on a high-volume programmatic advertising platform serving 1.2 billion+ transactions/month.
  • Led a team of 6 engineers to architect and build the next-generation ad server on a JavaScript (ES6) stack; migrations and cutovers ran with no service disruption on my watch.
  • Automated global deployment of a dockerized ad server across GCloud regions. Designed and executed lossless, backward-compatible cloud migrations (AWS ↔ GCloud) with no service disruption and no data loss while the platform handled billions of transactions globally.
  AWS, GCloud, JavaScript, Node.js, MongoDB, Docker

• Full-Stack Engineer

  StarterSquad, Sep 2013 to May 2017 · Remote (Europe / US clients)
  • Built a dairy industry startup MVP in one week (Netherlands); Series A of €4M followed two months later.
  • Delivered across multiple client teams and stacks: Angular, Meteor, React, Vue, Smalltalk, Swift, PostgreSQL, MongoDB, and RESTful APIs.
  Swift, React, Meteor, Angular, Vue, CircleCI

• Founder & Engineer

  Airflowing, 2009 to 2015 · Argentina / Brazil
  • Bootstrapped a B2B SaaS for service-company operations on Pharo Smalltalk. Designed, built, and operated the full system solo: ACID-compliant persistence, sub-second rendering, horizontally scalable. Grew to early customers; shut down after failing to scale sales without a co-founder. Open-sourced core work as Flow and Mapless.
  Smalltalk, Seaside, MongoDB, Product Design, UX/UI Design

• Earlier

  2001 to 2008
  • Lead engineer, toll system (2001 to 2006): Client-server PLC replacement for a road concession; Dolphin Smalltalk + PostgreSQL; fault-tolerant real-time hardware control.
  • Medical practice management (2007): Cheshire II-inspired probabilistic search (UC Berkeley) for relevance-ranked health content: non-boolean, sub-second results.
  • Ford aftermarket e-commerce (2006): Desktop B2B ordering app for Argentina's auto-parts market leader, delivered in 2 months.

Open Source & Side Projects

• Mapless (Smalltalk): Schema-less persistence framework for Pharo/Squeak. Community-maintained.
• Flow (Smalltalk): Full-stack web framework for Pharo with built-in persistence and productivity tooling.
• Shakedown (Rust): System-testing library with macro-first tests, testcontainers (Kafka, Postgres, Redis), and Toxiproxy fault injection. In active development.
• Astra (Rust): Smalltalk-like DSL compiling to async Rust actors (lexer/parser, AST, codegen).
• alphavantage_rs (Rust): Strongly typed Alpha Vantage API client. Targeting crates.io. MIT.

Writing

• blog.sebastiansastre.co: Systems engineering, Rust, CI, and delivery process. Recent: The Half of CI We Forgot to Automate, The Cost of Indirection in Rust, Your Turn.

Education & Certifications

• Machine Learning: Stanford University / Coursera (Andrew Ng) · 92% · Verify
• Design Thinking Action Lab: Stanford University
• CS193P iOS Development: Stanford University