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Run isolated sandboxes with full lifecycle control: AWS Lambda introduces MicroVMs | Amazon Web Services (opens in new tab)

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AWS Lambda MicroVMs provide isolated, stateful execution environments for running untrusted user- or AI-generated code without managing virtual machine infrastructure. Built on Firecracker, they combine VM-level isolation, near-instant startup and resume, and persistent memory and disk state. The post concludes that MicroVMs fill the gap between slow, isolated VMs, less-secure containers, and stateless event-driven Lambda functions.

The Need for Isolated, Stateful Execution

  • AI coding assistants, online development environments, analytics tools, vulnerability scanners, and game servers increasingly need a dedicated environment for each user or session.
  • Traditional options involve tradeoffs:
    • VMs provide strong isolation but often take minutes to start.
    • Containers launch quickly but share a kernel and require extensive hardening for untrusted workloads.
    • Standard serverless functions are designed for short, request-response workloads rather than long-running interactive sessions.
  • Building custom virtualization infrastructure requires significant security, operations, and virtualization expertise.

What Lambda MicroVMs Provide

  • Each user or session receives its own Firecracker-powered MicroVM.
  • MicroVMs offer:
    • Dedicated VM-level isolation with no shared kernel between users.
    • Rapid launch and resume from a pre-initialized snapshot.
    • Persistent memory, disk state, and running processes during a session.
    • Automatic suspension during inactivity to reduce idle costs.
    • Automatic resume when new traffic arrives.
  • Firecracker already powers AWS Lambda at large scale, providing an established virtualization foundation.

Creating a MicroVM Image

  • The example packages a Flask application and Dockerfile into a ZIP archive and uploads it to Amazon S3.

  • The Dockerfile uses:

    FROM public.ecr.aws/lambda/microvms:al2023-minimal

  • It installs Python and dependencies, copies the Flask application, and starts it with Gunicorn on port 5000.

  • An image is created with the aws lambda-microvms create-microvm-image command, specifying:

    • The S3 code artifact
    • An image name
    • An AWS-provided base image ARN
    • An IAM build role

  • Lambda builds the image, initializes the application, and captures its memory and disk state in a Firecracker snapshot.

  • Build logs are available in CloudWatch under /aws/lambda/microvms/<image-name>.

Launching and Managing a MicroVM

  • A MicroVM is launched from the image ARN with run-microvm.
  • The example configures an idle policy that:
    • Suspends the MicroVM after 15 minutes of inactivity.
    • Keeps it suspended for up to 5 minutes.
    • Automatically resumes it when traffic returns.
  • Lambda assigns a unique MicroVM ID and provides a dedicated HTTPS endpoint.
  • No separate networking setup is required.
  • The application is already running when the MicroVM becomes available because it resumes from the image snapshot.

Request Handling and State Preservation

  • Clients authenticate requests using a short-lived token in the X-aws-proxy-auth header.
  • The Flask API responds immediately after launch.
  • When the MicroVM becomes idle, Lambda snapshots and stores its memory and disk state.
  • A later request resumes the environment with the application state intact, making suspension effectively invisible to the client.

Underlying Execution Model

  • Lambda MicroVMs use an image-then-launch workflow:
    • Build and initialize an environment once.
    • Snapshot the initialized state.
    • Launch future MicroVMs by resuming that snapshot.
  • This avoids repeating operating-system and application startup work.
  • The combination of Firecracker isolation, snapshot-based startup, and suspend/resume lifecycle control makes MicroVMs suitable for secure, interactive, multi-tenant workloads.

For applications that must safely execute untrusted code while preserving session state and responsive startup times, Lambda MicroVMs offer a managed alternative to building custom VM infrastructure.