[ILLUM1N0X]

Part of #777

setup-gcp gave atelet object admin on the snapshot bucket and on the whole project, so root on a node could read and write every snapshot without the credential exchange. atelet only needs its own identity for micro-VM sandbox assets, which lived in the snapshot bucket. On GKE they now move to a bucket of their own, <BUCKET_NAME>-assets, which setup-gcp creates and lets atelet read, and atelet gets no other storage role. Snapshot transfers already run on per-actor tokens from the exchange.

Breaking change

On GKE with micro-VM workers, recreate the cluster. Substrate does not upgrade a cluster in place, and a node keeps fetching micro-VM assets from the snapshot bucket, since their digests do not change when they move. Run go run ./tools/setup-gcp create bucket and create iam before hack/install-microvm-deps.sh --install or a micro-VM demo, since assets are now staged in <BUCKET_NAME>-assets, which those commands create. On any existing install, gVisor-only included, run create bucket before rerunning create iam, which now also grants on the asset bucket and stops if it is missing. setup-gcp also refuses a BUCKET_NAME longer than 56 characters, since the asset bucket name would exceed GCS's limit.

Existing installs keep atelet's old grants, since setup-gcp only adds bindings. Once Substrate runs a release whose node plugin gets snapshot credentials from the credential exchange, and micro-VM assets are in the asset bucket, remove them:

ATELET="principal://iam.googleapis.com/projects/${PROJECT_NUMBER}/locations/global/workloadIdentityPools/${PROJECT_ID}.svc.id.goog/subject/ns/ate-system/sa/atelet"
gcloud projects remove-iam-policy-binding "${PROJECT_ID}" --member="${ATELET}" --role=roles/storage.objectAdmin --condition=None
gcloud storage buckets remove-iam-policy-binding "gs://${BUCKET_NAME}" --member="${ATELET}" --role=roles/storage.objectAdmin
gcloud storage buckets remove-iam-policy-binding "gs://${BUCKET_NAME}" --member="${ATELET}" --role=roles/storage.bucketViewer

Tested on a GKE cluster with atelet's storage grants removed: atelet's identity was refused on the snapshot bucket and could read the asset bucket, a micro-VM actor booted from the asset bucket, suspended to a completed durable snapshot and resumed, and the full e2e suite passed.

AI use: AI-assisted, I reviewed it.

• Tests pass
• Docs updated

[Huy Pham (hdp617)]

cc noahlwest for #2092.