Backend Engineer

Backend Engineer

Work on Windmill's Rust backend - the execution engine, workers, language runtimes, API layer, and infrastructure that powers thousands of production deployments.

Key Responsibilities

• Execution engine: scheduling, job queues, worker orchestration, flow execution with branching, parallelism, retries, and error handling.
• Language runtimes: maintain and extend sandboxed runtimes for Python, TypeScript, Go, Bash, SQL, and more.
• Performance & reliability: profiling, optimization, resource management. Our users run mission-critical workloads - correctness and uptime matter.
• Infrastructure: PostgreSQL schema design, caching, networking, deployment tooling.

Who we're looking for

This is a senior role. We're looking for someone who has operated distributed systems at scale and can teach us from day one - showing us PostgreSQL patterns, distributed systems techniques, and architectural improvements we haven't considered yet.

• Proven experience building and operating distributed systems at scale - not theoretical, you've done it in production
• Deep PostgreSQL expertise - query optimization, schema design, concurrency control, partitioning, replication. You know what breaks at scale and how to fix it.
• Strong systems programming skills - Rust experience strongly preferred, otherwise C/C++ with willingness to switch
• You bring opinions and techniques from previous infrastructure work that will make Windmill better immediately
• You enjoy hard infrastructure problems and care about correctness

Example projects in your first 3 months

• Redesign the job queue to handle bursty workloads with thousands of concurrent jobs without degrading scheduling latency
• Implement a new worker orchestration strategy that improves resource utilization across heterogeneous deployments (2 to 600 workers)
• Optimize critical PostgreSQL queries and schema for customers with millions of completed jobs - partitioning, indexing, vacuum tuning
• Add a new language runtime (e.g., Java, C#) with proper sandboxing, dependency management, and execution feedback
• Build observability tooling - distributed tracing across the flow execution engine to diagnose slow or failing steps in production

Offer details

Location: Paris hybrid (~3 days/week) or remote within France

Contract: CDI (permanent)

Salary: €60K--€90K gross + top of market for level + 20% bonus on collective milestones