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docs(cache): dedicated public bucket (don't expose user-builds) #191

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mdheller merged 1 commit into from
Jun 22, 2026
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docs(cache): dedicated public bucket (don't expose user-builds) #191

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23 changes: 18 additions & 5 deletions docs/NIX_CACHE_SETUP.md
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Expand Up @@ -18,21 +18,34 @@ in the meantime.
(using the workflow's existing WIF GCP auth). `build-custom-image.sh` calls it
after every build, so both the GitHub and GCP build lanes seed the cache.

> **Status (2026-06-22): this is already provisioned.** The cache lives in a
> **dedicated** public bucket `gs://sourceos-nix-cache-socioprophet` (NOT the
> artifacts bucket, which holds private `user-builds/` and stays private). The
> Actions vars/secrets below are set, and the keys are stored locally in
> `~/.sourceos-keys/`. The steps remain here for rotation / re-provisioning.

## One-time setup
1. **Generate a cache key pair** (ed25519, Nix's own format):
```sh
nix-store --generate-binary-cache-key sourceos-nix-cache-1 cache-secret.key cache-public.key
cat cache-public.key # e.g. sourceos-nix-cache-1:AbC123...=
```
2. **Make the cache prefix public-read** (pull is anonymous HTTPS):
2. **Use a DEDICATED public bucket** — never make the artifacts bucket public
(it contains private user builds). Create one and make only it public-read:
```sh
gsutil iam ch allUsers:objectViewer gs://sourceos-artifacts-socioprophet
# (or scope a bucket policy to the nix-cache/ prefix)
gcloud storage buckets create gs://sourceos-nix-cache-socioprophet \
--location=us-central1 --uniform-bucket-level-access
gcloud storage buckets add-iam-policy-binding gs://sourceos-nix-cache-socioprophet \
--member=allUsers --role=roles/storage.objectViewer
# let the CI service account push closures:
gcloud storage buckets add-iam-policy-binding gs://sourceos-nix-cache-socioprophet \
--member=serviceAccount:sourceos-ci@socioprophet-platform.iam.gserviceaccount.com \
--role=roles/storage.objectAdmin
```
3. **Set repo Actions variables** (Settings → Secrets and variables → Actions → Variables):
- `NIX_CACHE_URL` = `https://storage.googleapis.com/sourceos-artifacts-socioprophet/nix-cache`
- `NIX_CACHE_URL` = `https://storage.googleapis.com/sourceos-nix-cache-socioprophet/nix-cache`
- `NIX_CACHE_PUBKEY` = the `sourceos-nix-cache-1:…` line from step 1
- `NIX_CACHE_BUCKET` = `sourceos-artifacts-socioprophet`
- `NIX_CACHE_BUCKET` = `sourceos-nix-cache-socioprophet`
4. **Set the push secret** (Settings → Secrets → Actions → Secrets):
- `NIX_CACHE_SECRET_KEY` = contents of `cache-secret.key`
5. Optional but recommended — **seed the editions** once so the first user
Expand Down