#actions-runner

Guest image for GitHub Actions jobs that run in a microVM. See the Dockerfile header for the two targets.

#What the image holds

• The Actions runner at /opt/actions-runner, pinned by version and sha256. Bump RUNNER_VERSION and RUNNER_SHA256 together; the digest is in the release notes. Node is pinned the same way (NODE_VERSION with NODE_SHA256 from SHASUMS256.txt), and pnpm to an exact version.
• git, node, pnpm, jq, gh, python3 and a C toolchain.
• systemd as init. The microVM boots it, and the guest agent that talks to the host is installed as a unit when the root filesystem is baked.

It holds no credentials. The runner starts with run.sh --jitconfig, using a one-job configuration that arrives with the job, takes that job and exits.

#Making a root filesystem

docker build --target actions-runner -t actions-runner packaging/actions-runner
cid=$(docker create actions-runner)
docker export "$cid" | (mkdir rootfs && tar -x -C rootfs)
docker rm "$cid"
truncate -s 8G actions-runner.ext4
mkfs.ext4 -F -d rootfs actions-runner.ext4

The host-side tooling then installs the guest agent into the image and snapshots it. That step lives with the runner, not here.

#Egress

Inside the microVM the runner reaches the network only through the host's allowlisting proxy, through HTTPS_PROXY. A workflow that needs a host beyond the allowlist fails at connect time.