AWS Lambda
The FaaS pioneer — upload a function, AWS runs it on events (HTTP, S3, queue, schedule). Billed per millisecond of execution.
Launched re:Invent 2014. Supports Node, Python, Java, Go, Ruby, .NET, custom runtimes (Bash, Rust). Built on Firecracker microVMs since 2018 — cold start 100–500 ms depending on language. SnapStart (Java 11+) caches pre-init state.
Sweet spot: event-driven workflows, glue between services, sporadic traffic. Trade-offs: cold start, 15-minute max execution, 250 MB package limit. Much more openly hated since the 2020s — many shops migrate back to container-based services (ECS, Cloud Run).