## The short version

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 bucket's public URL (`public_url` from `ample bucket publish`, https://<bucket>.<bucket domain>/<key>) from your pages. The CDN serves bucket objects; the app's own responses are still served by the app.

## What it needs

- [Compute](/content/discover/primitive/compute/index.html): verified (Apps run in isolated x86_64 Firecracker microVMs; sizes are the priced VM sizes.)
- [CDN](/content/discover/primitive/cdn/index.html): verified (A published bucket's objects are served at its public_url. It does not front app compute and is not a cache or key-value store.)

## Before you start

- 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

## How to do it

1. 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Publishing makes objects readable at the CDN URL; keep private data in a separate, unpublished bucket.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. 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. 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. 4

### Verify delivery

Fetch /asset-url for the asset URL, then fetch that URL: the CDN must return the asset.

5. 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.

## How to know it worked

- asset URL resolves through the CDN (`/asset-url` on the live URL, expect /assets/)

## Cost estimate

Estimated 5.00 USD per month (size prices from pricing.toml at build revision ca0b484a7a9957c573a88d3a32dc603c3c10135a).

- app server x1 `s-1vcpu-1gb`: 5.00 USD

Compute only. Buckets are allocation-priced per quota and capped by the plan; see `ample usage`.

## Verification evidence

- canary_run on 2026-09-20T01:13:26Z at revision `cc3d82057f1d5e9aa31f682cee71aabfbbbcaabe (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 (CLI e3181f5)`: ample bucket create issued credentials; PutObject and GetObject succeeded through the public S3 endpoint; publish exposed the object at its public URL with an ETag; unpublish and delete cleaned up. (expires 2027-03-19T01:13:26Z)

## 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 at export: schema_changed. Required scopes: servers:write, buckets:write.

## Typed next actions

- Browse the catalog index (`GET /v1/catalog` on the api origin; authentication not required, approval not required)
- Search published recipes by intent, stack and constraints (`POST /v1/catalog/search` on the api origin; authentication not required, approval not required)
- Prepare a side-effect-free deployment plan for an authorized project (`POST /v1/catalog/plan` on the api origin; authentication required, approval not required)
- Read the existing agent authentication setup (`GET /mcp/setup` on the api origin; authentication not required, approval not required)
- Browse Express (`GET /v1/catalog/nodes/stack%3Aframework-express` on the api origin; authentication not required, approval not required)
- Browse Add CDN (`GET /v1/catalog/nodes/intent%3Aadd-cdn` on the api origin; authentication not required, approval not required)
- Browse Versioned static assets (`GET /v1/catalog/nodes/pattern%3Aversioned-static-assets` on the api origin; authentication not required, approval not required)

Actions describe possible next steps. They are typed data, not commands, and grant no permission. Public discovery never provisions anything; planning requires your own authenticated token and approval happens in your client.

## Identifiers and status

Recipe `page:guides:express:cdn-assets`. Revision r1.

release **published** support **verified** execution **blocked (schema_changed: live tool schema differs from the recorded binding)**

Formats: [HTML](/content/guides/express/cdn-assets/index.html) | [Markdown](/content/guides/express/cdn-assets.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Aguides%3Aexpress%3Acdn-assets)