# Deliver public assets through CDN for Express

## Summary

Deliver public assets for a Express app through the Ample CDN. Publish a bucket with `ample bucket publish`, upload versioned assets with long-lived Cache-Control headers, and reference the CDN URL (https://cdn.<base>/<bucket-id>/<key>) from your pages. The CDN serves bucket objects; the app's own responses are still served by the app.

## Infrastructure requirements

- [Compute](/content/discover/primitive/compute/index.html): verified (Apps run in isolated x86_64 Firecracker microVMs that auto-pause when idle and wake on request; sizes are the priced VM sizes.)
- [CDN](/content/discover/primitive/cdn/index.html): verified (The CDN host serves objects from published buckets. It does not front app compute and is not a cache or key-value store.)

## Prerequisites

- A bucket created with `ample bucket create` and published with `ample bucket publish` (its public URL is the CDN base)
- An S3 client in the app to upload assets under versioned keys
- An Ample account token with servers:write and buckets:write

## Exact tested configuration

- template: `node-22`
- runtime: `node`
- size: `s-1vcpu-1gb`
- install: `npm install`
- build: `npm run build --if-present`
- start: `npm run start`

## Steps

1. **Publish the bucket.** Publishing makes objects readable at the CDN URL; keep private data in a separate, unpublished bucket.
   
   ```
   ample bucket publish <bucket-name>
   ```
2. **Upload versioned assets.** Use keys such as assets/<version>/file and set Cache-Control: public, max-age=31536000, immutable; change the version to invalidate.
3. **Reference the CDN URL.** Pass S3_PUBLIC_URL to the app and build asset URLs from it.
   
   ```
   ample deploy . --name <app-name> --public --env S3_PUBLIC_URL=... --env S3_ENDPOINT=... --env S3_REGION=... --env S3_BUCKET=... --env S3_ACCESS_KEY_ID=... --env S3_SECRET_ACCESS_KEY=...
   ```
4. **Verify delivery.** Fetch /asset-url for the asset URL, then fetch that URL: the CDN must return the asset.
5. **Verify.** Fetch the live URL and run the success checks below. On failure read the build log, then the runtime log, fix the cause and deploy again; do not blind-retry.
   
   ```
   ample logs <deployment_id> --kind build
   ```

## Tested examples

- **Express CDN assets canary** (tests/deploy-canaries/express-cdn-assets): Versioned asset uploaded to a published bucket and served from the CDN URL.

## Success checks

- asset URL resolves through the CDN (`/asset-url` on the live URL, expect https://cdn.)

## Limitations

- Verified on the node-22 template at s-1vcpu-1gb; other templates and sizes are not verified by this recipe.
- Region, compliance attestations and request-duration limits are unknown and not claimed.
- Apps auto-pause when idle and wake on the next request; always-on is an operator setting, not a plan feature.
- PutObject and GetObject with path-style addressing are verified; multipart upload, listing, presigned URLs and lifecycle rules are not verified.
- Bucket credentials are passed as encrypted environment variables; the catalog never creates the bucket for you (use `ample bucket create`).
- Storage is allocation-priced per bucket quota and capped by the account plan; the estimate below covers compute only.
- The CDN serves objects from a published bucket only; it does not front the app's own responses.
- Cache rules, purge and TTL control are not verified; the fixture sets Cache-Control on upload and versions asset keys instead.

## Cost estimate

Estimated 5.00 USD per month (size prices from pricing.toml at build revision a1b8c38919e59cd035ebabaced73cf84ece24371).
- app server x1 `s-1vcpu-1gb`: 5.00 USD

## Verification evidence

- canary_run on 2026-09-20T01:13:26Z at revision `cc3d82057f1d5e9aa31f682cee71aabfbbbcaabe-dirty (CLI e3181f5)`: Express app uploaded a versioned, immutable-cached asset to a published bucket at startup; the CDN URL it returned served the asset publicly. (expires 2027-03-19T01:13:26Z)
- canary_run on 2026-09-20T01:13:26Z at revision `cc3d82057f1d5e9aa31f682cee71aabfbbbcaabe-dirty (CLI e3181f5)`: ample bucket create issued credentials; PutObject and GetObject succeeded through the public S3 endpoint; publish exposed the object through the CDN host with an ETag; unpublish and delete cleaned up. (expires 2027-03-19T01:13:26Z)

Last verified: 2026-09-20T01:13:26Z

## Execution binding

MCP tool `ample_deploy` (registry `mcp:ample_deploy`), schema hash `876465fce906da0c` observed 2026-09-20T01:55:48.667900+00:00 at revision `199ff1dfd526`, binding state `current`, required scopes: servers:write, buckets:write.