AWS Lambda MicroVMs: run untrusted code with VM-level isolation (no infra to manage)

AWS just shipped Lambda MicroVMs, a new serverless primitive that gives each user or session a VM-level isolated sandbox, with near-instant launch and state preserved for up to 8 hours, all on Firecracker. Here is what it is, when to reach for it instead of a plain Lambda Function, and how to architect on top of it.