PostHog is looking for a high-performance backend engineer to build and scale systems that need to respond in single-digit milliseconds at scale for their Feature Flags team. The goal is to ensure the feature flags evaluation engine can handle millions of requests per minute without breaking a sweat, directly impacting customer user experience.
Requirements
- experience with high-throughput, low-latency services similar to: Real-time bidding platforms, Payment processing systems, Recommendation engines, Authentication services, Content delivery networks
- experience with any systems programming language and/or backend web frameworks.
- built systems that handle high volumes of requests/data (millions+ per minute)
- strong understanding of performance optimization techniques, caching strategies, and distributed systems principles
- worked with feature flag systems or similar real-time decision engines
- comfortable with provisioning, tuning, and deploying infrastructure
- worked with benchmarking and profiling tools
Responsibilities
- 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.
- building and maintaining our feature flags evaluation engine that makes complex decisions based on person/group properties at high speed and scale.
Other
- 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.
- You can choose a sensible architecture quickly, and then ship it faster than other people think is possible
- actively participated in on-call rotations, and have dealt with and resolved production incidents
- solid understanding of observability systems and practices
