Everything you know about observability needs a slight rethink when you move to serverless. Let me save you the weeks of frustration I went through. Cold starts matter now Your p99 latency is dominated by cold starts. A function that runs in 50ms warm can take 2 seconds cold. If you measure latency without splitting warm vs cold, your metric is lying to you. Instrument: request_duration_ms tagged with cold_start: true|false . Alert on warm p99, not blended p99. No persistent process, no persistent buffers Your usual tracing SDK probably buffers events and flushes periodically. On serverless, the runtime can die between invocations. You lose the buffered events. Fix: flush at the end of every invocation, synchronously. Yes, it adds latency. Yes, it's worth it. Logs are your friend, not your traces Traces are hard across serverless boundaries. Events are not. If your architecture is heavily event-driven, invest in structured logging and a log-based observability pattern before you invest in traces.…