posthog - Backend Engineer - Europe/UK Timezone
Requirements
• We're looking for a backend engineer excited about systems that answer in single-digit milliseconds, millions of times a minute, without breaking a sweat. Our feature flags evaluation service sits in the critical path of every customer's app. When it's slow, their product is slow. When it's down, they can't ship. That responsibility should motivate you, not terrify you. • You've built high-throughput, low-latency services where correctness and tail latency both matter: real-time bidding, payment processing, recommendation engines, auth services, or CDNs. • We write Rust and Python, plus a pile of client SDK languages (JS/TS, Go, Ruby, PHP, Java, .NET, iOS, Android, Flutter, and more). You don't need all of them, but you should be a polyglot (or happy to become one) who cares about developer experience as much as performance. Flags should be trivial to add, obvious to manage, and impossible to forget about. • You've built and operated systems that handle high volumes of requests or data (millions+ per minute), and you care about tail latency, caching, and distributed systems failure modes • You're productive in Rust and Python, or confident you'll get there fast. While the app is Django, the evaluation engine and much of our backend infrastructure is in Rust or moving to it. • You work independently. You can pick a sensible architecture, ship it faster than people expect, and drive it to done without being managed • You ship changes quickly without breaking a service customers depend on to launch • You're based in a European time zone • Experience with feature flags, customer data platforms, or other real-time decision engines • You've carried a pager and dealt with incidents • You're comfortable provisioning and maintaining cloud infrastructure • Experience with benchmarking and profiling tools • If this sounds like you, we should talk. • We are committed to ensuring a fair and accessible interview process. If you need any accommodations or adjustments, please let us know.
Responsibilities
• Our team is distributed. For this role we're hiring in European time zones to balance the team. You'll overlap with teammates daily, but much of your day is solo. You need to own your work without someone setting the agenda. • We build the feature flag tools, SDKs, evaluation services, and in-app UI that customers use to safely ship features and make data-driven decisions. We own the reliability, stability, and performance of the targeting service and local evaluation endpoints, end to end. You won't maintain a small corner of a massive system. You'll own whole services and set their latency and uptime targets yourself. • Some of what we’re working on: • Real-time cohorts, our most-requested feature. Membership is computed on a delay today, which makes it useless for targeting like "users who did X in the last five minutes." Evaluating it in real time at flag-check time collapses a whole category of custom targeting logic people build themselves. • Moving from a read-heavy to a write-heavy architecture, including a dedicated store for flag evaluation so we're not coupled to the shared Persons DB. • An AI-first flag management tool we're dogfooding internally, so agents can create, modify, and reason about flags without ever opening the UI. • Reliability and performance work to lower our p50/p90/p99 latencies and isolate the evaluation path from upstream failures (load shedding, request hedging, decoupling from the Persons DB). • One day you're making an architecture call, the next you're cutting p99 latency in half, the day after you're porting cache building to Rust.
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