[Kevin Cho (chokevin)]

Repeated GB200 repaves could boot Ubuntu but did not have a reproducible, qualified host image that restored the reviewed lab access policy. The image now bakes native cloud-init users into an ARM64 Ubuntu disk, while MetalMan fails closed before destructive replacement if Machine user-data could override those users; generic host images keep their existing user-data behavior.

• Adds a reproducible Ubuntu 24.04 ARM64 GB200 disk producer and a dedicated access-policy derivative with pinned kernel, NVIDIA, and ssh-import-id inputs.
• Uses native per-user ssh_import_id configuration. The intentionally keyless account remains locked without failing cloud-init.
• Protects only the dedicated image repository from top-level users, multiple YAML documents, trailing YAML, and cloud-init templating. ConfigMap API failures remain retryable; permanent policy violations fail before power actions.
• Preserves the generic MetalMan unbounded-metal vendor user and existing custom/templated user-data behavior for other images.
• Extends the image workflow with native ARM64 provenance checks and an ARM64 UEFI/QEMU gate covering cloud-init, networking, SSH, valid authorized keys, MANA, NVIDIA, and the MetalMan vendor-data path.

Evidence

The 15-second recording shows the baked cloud-init policy, actual fail-closed preflight results, and the exact ARM64 disk qualification evidence.

gb200-host-access.mp4

Verification

• Passed: go test ./internal/metalman/... ./hack/cmd/hostimage-userdata-preflight ./hack/hostimage
• Passed: 41 GB200 producer Python tests and 3 vendor-data renderer tests
• Passed: pinned gofumpt, shell syntax, ShellCheck, YAML parsing, and git diff --check
• Passed: exact-commit native ARM64 OCI build and provenance checks
• Passed: ARM64 UEFI/QEMU boot gate for 64K kernel, cloud-init final stage, systemd-networkd, SSH, MANA, NVIDIA, user creation, and valid authorized keys
• Qualified disk SHA-256: 0afd7577f85783689755d25fc7b98d613949738e11db121210b223760a19ee81
• Not run: repository-wide make fmt; the pinned golangci-lint cannot decode the repository's Go 1.27 export data. Changed Go files were formatted with the pinned gofumpt, and the broad MetalMan test suite passed.

Risk

The strict user-data policy is repository-scoped to ghcr.io/azure/host-ubuntu2404-gb200-hillsboro; generic images retain their prior behavior. This PR does not publish an image or mutate a Machine. Publication remains a manual, gated workflow, and any image activation or HostReplace requires a separate operational decision.

Review guide

1. Start with internal/metalman/cloudinit/userdata.go and internal/metalman/machineops/controller.go for policy scope, error classification, and pre-side-effect validation.
2. Review images/host-ubuntu2404-gb200-hillsboro/ for the baked user policy and deterministic boot qualification.
3. Check .github/workflows/images.yaml and images/host-ubuntu2404-gb200/verify-boot.sh for the publish gate.
4. Review internal/metalman/{cloudinit,machineops,netboot}/*_test.go for bypass, retry, and generic-image compatibility coverage.

AI assistance: GitHub Copilot helped implement, test, review, and draft this change; the author verified the claims, validation results, and final text.