Building an AWS Lambda-Like Runtime with Firecracker MicroVMs

3 days ago

Built a lightweight serverless runtime using Firecracker microVMs to understand serverless platforms better.
Firecracker offers fast boot times and strong isolation, ideal for running untrusted code in serverless environments.
Cold start latency (~200ms) was reduced to ~1–5ms using snapshot restores, improving performance 40–200x.
System architecture includes a control plane and execution layer communicating via vsock.
Challenges included PID 1 issues solved with tini, snapshot timing dilemmas, and vsock IPC race conditions.
Runtime design uses Node.js inside microVMs, with warm runtime reuse to boost throughput and latency.
Multi-tenant scheduling implemented per-function queues, concurrency limits, and weighted scheduling.
Benchmark results show ~5,400 req/s throughput, p50 latency ~1ms, and p99 latency ~4ms.
Trade-offs considered include isolation vs. throughput and runtime flexibility vs. complexity.
Project provided deep insights into cold starts, isolation-performance tension, and observability in minimal systems.

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