Backend Engineer - Feature Flags

About Posthog

We equip every developer to build successful products.

We started with open-source product analytics, launched out of Y Combinator's W20 cohort.

We've since shipped more than a dozen products, including a built-in data warehouse, a customer data platform, and Max AI, an AI-powered analyst that answers product questions, helps users find useful session recordings, and writes custom SQL queries.

Next on the roadmap are messaging, customer analytics, ai task creation and coding based on customer data, logs and support analytics.

Our values are not a poster on the wall full of aspiration. They’ve come from how we really work, day in day out.

PostHog is open source product led, and a default alive company that is well funded.

Who We’Re Looking For

We're seeking a high-performance backend engineer for our Feature Flags team (led by Dylan Martin) who thrives on the challenge of building systems that need to respond in single-digit milliseconds at scale. You're the type of engineer who gets excited about profiling applications, getting clever with data access patterns, shaving microseconds off response times, and designing elegant systems that can handle millions of requests per minute without breaking a sweat.

The ideal candidate has experience with high-throughput, low-latency services similar to:

• Real-Time Bidding Platforms

• Payment Processing Systems

• Recommendation Engines

• Authentication Services

• Content Delivery Networks

You're not just a performance optimizer - you care deeply about clean architecture, observability, and creating APIs that developers love to use and applications rely on. You understand that in the feature flags world, your code is in the critical path of every customer's user experience, and you take that responsibility seriously.

What Makes This Role Unique

Unlike many high-scale API engineering roles where you're maintaining a small part of a massive system, at PostHog you'll:

• Own the entire service from end-to-end: Design, build, deploy, and scale the feature flags evaluation engine.
• Build in the hot path with real impact: Your code runs in the critical path of our customers' applications, making a direct impact on their user experience.
• Start from first principles: Scale up new services from the ground up rather than just maintaining existing infrastructure.
• Set your own performance targets: You won't be constrained by other teams' requirements - you'll define and own the latency goals that make our customers successful.
• See immediate results: Deploy optimizations and see the impact on performance metrics in real-time.
• Work with cutting-edge tech: Most of our performant stuff (e.g. our flags evaluation endpoint) is written in Rust (Dylan wrote a great blog post about it!), while our application layer uses Python/Django.

What You'Ll Be Doing

Our engineering team is distributed across the Americas, and we are open to candidates based anywhere in GMT-8 and GMT+2 time zones. You'll collaborate with a distributed team that's passionate about building world-class developer tools.

We're growing very quickly at PostHog, and our Feature Flags service is scaling rapidly. You'll be responsible for building and maintaining our feature flags evaluation engine that makes complex decisions based on person/group properties at high speed and scale.

We recently rewrote the service in Rust (yep, that’s the same blog post again, it’s really worth a read 😅) and are working on adding new targeting features and continuing to improve the latency. You'll be working on a critical part of our infrastructure that customers rely on for real-time feature delivery. One day, you'll be making high-level architecture decisions, the next you'll be optimizing a performance bottleneck that slashes latency by 50%, and the day after you'll work directly with customers to implement complex targeting rules that meet their specific needs.

You’Ll Fit Right In If:

• You have experience with any systems programming language and/or backend web frameworks. We use Python and Rust a lot – our app is written in Django, and the flags evaluation API is written in Rust – so experience in those languages is a plus, but not required
• You’ve built systems that handle high volumes of requests/data (millions+ per minute)
• You can choose a sensible architecture quickly, and then ship it faster than other people think is possible
• You have a strong understanding of performance optimization techniques, caching strategies, and distributed systems principles

Nice To Have

• You worked with feature flag systems or similar real-time decision engines
• You actively participated in on-call rotations, and have dealt with and resolved production incidents
• You're comfortable with provisioning, tuning, and deploying infrastructure
• You worked with benchmarking and profiling tools
• You have a solid understanding of observability systems and practices

What’S In It For You?

Now that we've told you what you'll be building with us, let's talk about what we'll be building for you.