substrate/docs/dev/microvm-local.md

Running the microVM runtime locally

The microVM sandbox class (ateom-microvm: a Kata guest on Cloud Hypervisor) needs /dev/kvm, which takes some extra setup compared to the default gVisor path. This guide covers just that delta: getting a KVM-capable Docker environment — on Linux, or on Apple Silicon macOS via Lima — then running the microVM counter demo and verifying a guest-memory snapshot round-trip.

Prerequisites

Complete the Quickstart (Development) in the README first — it covers the base tooling and the default (gVisor) path this guide builds on. For background on the runtime, see architecture.md and hack/microvm-assets/README.md.

Option A: Linux host with KVM

Works on bare-metal Linux or any cloud VM with nested virtualization enabled (e.g. GCE N4/N4D instances with nested virt, or equivalent on other clouds).

1. Verify KVM

ls -la /dev/kvm
# Expected: crw-rw---- 1 root kvm 10, 232 ... /dev/kvm

grep -cE '(vmx|svm)' /proc/cpuinfo   # >0 means CPU virt support (x86)

hack/create-kind-cluster.sh probes for KVM by running a root container with --device /dev/kvm, which works out of the box with a standard (rootful) Docker install. With rootless Docker the container's root is remapped to your user, so the probe fails with permission denied — use rootful Docker instead, or open up the device with sudo chmod 666 /dev/kvm.

2. Create the cluster

./hack/create-kind-cluster.sh
# Look for: "/dev/kvm found: micro-VM (kata + cloud-hypervisor) support will be enabled."

Once the control plane is up, atelet advertises the device on each KVM-capable node, which is what places micro-VM workers:

kubectl get nodes -o jsonpath='{range .items[*]}{.metadata.name}{"\t"}{.status.capacity.ate\.dev/kvm}{"\n"}{end}'

3. Run the microVM demo

./hack/run-microvm-demo-kind.sh

This is a one-shot bring-up: it deploys the control plane, installs the cluster-wide microVM deps via hack/install-microvm-deps.sh — assembling the guest runtime assets for your architecture (skipped if already present under bin/microvm-assets/), staging them into the in-cluster rustfs bucket, and applying the microvm SandboxConfig — then deploys the demo worker pool + template.

4. Verify

kubectl get pods -n ate-demo-counter-microvm
kubectl get workerpools -A
kubectl ate get actor-templates -a ate-demo-counter-microvm

Expected:

NAMESPACE                  NAME                                 DESIRED  READY  AVAILABLE
ate-demo-counter-microvm   workerpool.ate.dev/counter-microvm   1        1      1

ATESPACE                   NAME              SANDBOX CLASS           GOLDEN SNAPSHOT                        ERROR   AGE
ate-demo-counter-microvm   counter-microvm   SANDBOX_CLASS_MICROVM   b9f6bd93-3c5a-4b64-9d5e-2f8a1c7d0e42           1m

The template is ready once the GOLDEN SNAPSHOT column is non-empty (the value is a UUID); ERROR means the golden build failed, and -o yaml shows the full error message. An empty GOLDEN SNAPSHOT with no ERROR means the golden build — a full guest boot plus checkpoint — is still running.

Option B: Apple Silicon macOS via Lima

Lima can run a Linux VM with nested virtualization, exposing /dev/kvm to Docker (and therefore to the kind node) inside the VM. This is a well-trodden path — much of Substrate's development happens on macOS via limactl.

Important

Apple's Virtualization framework supports nested virtualization only on M3 and later — on earlier Apple Silicon (M1/M2), Lima fails with [hostagent] Starting VZ ... FATA exiting. Fall back to Option A on a Linux host.

1. Install Lima and the Docker CLI

brew install lima docker

2. Launch Lima with nested virtualization

The arm64 nested-virtualization kernel regression affects kernels 6.19 and newer, so use a guest image with an older kernel — pinned here to Ubuntu 24.04 LTS:

limactl start --name=docker-nested template://docker-rootful --nested-virt --set '.images = [
{"location":"https://cloud-images.ubuntu.com/releases/noble/release/ubuntu-24.04-server-cloudimg-arm64.img","arch":"aarch64"},
{"location":"https://cloud-images.ubuntu.com/releases/noble/release/ubuntu-24.04-server-cloudimg-amd64.img","arch":"x86_64"}
]'

When prompted to edit the configuration, set at least:

cpus: 8
memory: "16GiB"
nestedVirtualization: true
networks:
  - vzNAT: true
mounts:
  - location: "~"
    writable: true

The writable home mount lets the kind/ko workflows write into your checkout, 8 CPUs / 16 GiB is a comfortable floor for the control plane plus a microVM worker, and vzNAT gives the VM outbound networking under the vz VM type.

3. Assemble the arm64 assets inside the Lima VM

hack/microvm-assets/assemble.sh must run on a Linux host of the target architecture (on arm64 it builds virtiofsd from source with cargo against Linux-only libraries), so run it in the Lima guest, not on macOS:

limactl shell docker-nested

# Inside the VM — install build deps once:
sudo apt-get update && sudo apt-get install -y git pkg-config libcap-ng-dev libseccomp-dev zstd
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh   # rust via rustup
source "$HOME/.cargo/env"

cd <your substrate checkout>    # visible via the writable home mount
./hack/microvm-assets/assemble.sh
exit

The assets land in bin/microvm-assets/arm64/ in your checkout, which is shared with the host through the home mount — the demo script will find them there and skip re-assembling.

4. Point the Docker CLI at Lima and bring everything up (on macOS)

export DOCKER_HOST="unix://${HOME}/.lima/docker-nested/sock/docker.sock"
echo 'export DOCKER_HOST="unix://${HOME}/.lima/docker-nested/sock/docker.sock"' >> ~/.zprofile

cd <your substrate checkout>

./hack/create-kind-cluster.sh
./hack/run-microvm-demo-kind.sh

Verify as in Option A, step 4.

Trying it out

On completion, run-microvm-demo-kind.sh prints next steps: create an actor from the counter-microvm template, hit the in-RAM counter, then suspend and resume it and confirm the count continues — proving the guest-memory snapshot round-tripped. The flow is the same as the README Quickstart, just with the microVM template; see the counter demo's micro-VM variant for background. Note that an actor template showing a GOLDEN SNAPSHOT in the verify step already exercises the runtime end-to-end — the golden snapshot requires a full guest boot and checkpoint.

Troubleshooting

Symptom	Root cause	Fix
/dev/kvm: permission denied during the kind KVM probe	Rootless Docker: the probe container's root is remapped to your user, which can't open the device (660 root:kvm)	Use rootful Docker, or sudo chmod 666 /dev/kvm before ./hack/create-kind-cluster.sh
cargo not found from assemble.sh	On arm64, virtiofsd is built from source	Install the build deps listed in Option B, Step 3
Lima: [hostagent] Starting VZ ... FATA exiting on M1/M2	Apple's Virtualization framework supports nested virtualization only on M3 and later	Use an M3+ Mac, or a Linux/KVM host (Option A)