---
title: "Configure S3-compatible access for Express"
description: "Configure S3-compatible access for a Express app on Ample."
canonical_url: "https://ample.computer/guides/express/object-client"
last_updated: "2026-09-20"
---

# Configure S3-compatible access for Express

Canonical URL: https://ample.computer/guides/express/object-client
Formats: [HTML](https://ample.computer/guides/express/object-client) | [Markdown](https://ample.computer/guides/express/object-client.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Aguides%3Aexpress%3Aobject-client)
Recipe ID: `page:guides:express:object-client` | Revision: `r1` | Catalog revision: `cat_f13ab9a494120b5e`

Status: release `published`, support `verified`, execution `ready`

## Summary

Configure S3-compatible access for a Express app on Ample. Create a bucket with `ample bucket create`, pass its endpoint, region, bucket name and keys as encrypted environment variables, and use @aws-sdk/client-s3 with forcePathStyle: true. The app writes and reads objects through the S3-compatible endpoint; the bucket stays private.

Path: [Agent hosting discovery](/discover/discovery) / [Frameworks and execution targets](/discover/stack) / [Frameworks](/discover/stack/frameworks) / [Express](/discover/stack/framework-express) / [Configure S3-compatible access for Express](/guides/express/object-client)

## Infrastructure requirements

- [Compute](/discover/primitive/compute): verified (Apps run in isolated x86_64 Firecracker microVMs that auto-pause when idle and wake on request; sizes are the priced VM sizes.)
- [S3-compatible object storage](/discover/primitive/s3-compatible-object-storage): verified (Buckets are S3-compatible with issued credentials; PutObject and GetObject are verified by canary. Other S3 operations are not verified.)

## Prerequisites

- An S3 client in the app (@aws-sdk/client-s3 with forcePathStyle: true) reading S3_ENDPOINT, S3_REGION, S3_BUCKET, S3_ACCESS_KEY_ID and S3_SECRET_ACCESS_KEY
- A bucket created with `ample bucket create <name>` and its credentials from `ample bucket credentials <name>`
- An Ample account token with servers:write and buckets:read

## 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. **Create the bucket.** Create it once and keep the issued credentials out of the repository.

   ```
   ample bucket create --name <bucket-name>
   ```
2. **Configure the client with path-style addressing.** Use @aws-sdk/client-s3 with forcePathStyle: true; virtual-host addressing is not verified.
3. **Deploy with the credentials as encrypted env.** Pass the five S3_* variables with --env; they are stored encrypted and reused on redeploys.

   ```
   ample deploy . --name <app-name> --public --env S3_ENDPOINT=... --env S3_REGION=... --env S3_BUCKET=... --env S3_ACCESS_KEY_ID=... --env S3_SECRET_ACCESS_KEY=...
   ```
4. **Test through the app.** Expose a route (/storage) that writes then reads an object and reports s3=ok.
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 bucket canary** (tests/deploy-canaries/express-bucket-uploads): Write and read an object with the injected credentials.

## Success checks

- object write and read succeed (`/storage` on the live URL, expect s3=ok)


## Cost estimate

Estimated 5.00 USD per month (size prices from pricing.toml at build revision 515b7316fc6e5a81679407ae0c811146ceb2c5c7).
- 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 using @aws-sdk/client-s3 with the bucket credentials injected as encrypted environment variables: PutObject then GetObject through the S3-compatible endpoint returned s3=ok. (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 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:read.

## Input schema

```json
{
  "additionalProperties": false,
  "properties": {
    "env": {
      "description": "Encrypted environment variables: S3_ENDPOINT, S3_REGION, S3_BUCKET, S3_ACCESS_KEY_ID, S3_SECRET_ACCESS_KEY from `ample bucket credentials` (and S3_PUBLIC_URL for a published bucket)",
      "items": {
        "pattern": "^[A-Z][A-Z0-9_]*=.*$",
        "type": "string"
      },
      "maxItems": 50,
      "type": "array"
    },
    "name": {
      "description": "App name (lowercase, digits and dashes)",
      "maxLength": 63,
      "minLength": 1,
      "pattern": "^[a-z0-9-]+$",
      "type": "string"
    },
    "path": {
      "description": "Project directory to deploy, or one service name from ample.toml",
      "maxLength": 512,
      "minLength": 1,
      "type": "string"
    },
    "size": {
      "description": "VM size; omit to let Ample pick a runtime-safe size",
      "enum": [
        "s-1vcpu-256mb",
        "s-1vcpu-1gb",
        "s-1vcpu-2gb",
        "s-2vcpu-2gb",
        "s-2vcpu-4gb"
      ],
      "type": "string"
    },
    "start": {
      "description": "Start command override when detection cannot infer it (Python apps pass one explicitly)",
      "maxLength": 512,
      "type": "string"
    }
  },
  "required": [
    "env",
    "name",
    "path"
  ],
  "type": "object"
}
```

## Next actions

- Browse the catalog index (GET /v1/catalog on the api origin; auth: false, approval: false)
- Search published recipes by intent, stack and constraints (POST /v1/catalog/search on the api origin; auth: false, approval: false)
- Prepare a side-effect-free deployment plan for an authorized project (POST /v1/catalog/plan on the api origin; auth: true, approval: false)
- Read the existing agent authentication setup (GET /mcp/setup on the api origin; auth: false, approval: false)
- Browse Express (GET /v1/catalog/nodes/stack%3Aframework-express on the api origin; auth: false, approval: false)
- Browse Connect app to storage (GET /v1/catalog/nodes/intent%3Aconnect-app-to-storage on the api origin; auth: false, approval: false)
- Browse Browser file uploads (GET /v1/catalog/nodes/pattern%3Abrowser-file-uploads on the api origin; auth: false, approval: false)

Actions describe possible next steps. They are typed data, not commands, and grant no permission.