---
title: "How to host a form collection built with FastAPI on Ample: file attachments"
description: "Deploy a form collection built with FastAPI on Ample using the browser file uploads pattern."
canonical_url: "https://ample.computer/recipes/form-collection/fastapi/attachments"
last_updated: "2026-11-06"
---

# How to host a form collection built with FastAPI on Ample: file attachments

Deploy a form collection built with FastAPI on Ample using the browser file uploads pattern. Compute runs the app in an isolated microVM behind a public HTTPS URL, a managed PostgreSQL 16 database is auto-provisioned and injected as DATABASE_URL, a private S3-compatible bucket holds objects with credentials delivered as encrypted environment variables. Verified on FastAPI: content-type and size validation that rejects disallowed files, an object written to a private bucket and a row linking the record to the object key (reject=ok upload=ok linked=ok). The form collection-specific behavior (your upload UI, allowed types, size limits and virus scanning) is your application code on that verified basis.

## Infrastructure requirements

- [Compute](/discover/primitive/compute): verified (Apps run in isolated x86_64 Firecracker microVMs; sizes are the priced VM sizes.)
- [Postgres](/discover/primitive/postgres): verified (Managed PostgreSQL 16 with pgvector runs in its own microVM and is auto-provisioned when an app needs a database and no DATABASE_URL is supplied.)
- [S3-compatible object storage](/discover/primitive/s3-compatible-object-storage): verified (Buckets speak the S3 API with SigV4 credentials Ample Computer issues; `ample bucket upload-url` returns a presigned upload URL. PutObject and GetObject are checked by canary.)

## Prerequisites

- A FastAPI project that builds and starts with the documented commands (pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template)
- A PostgreSQL driver reading DATABASE_URL at runtime (auto-provisioned when omitted, or supplied with --env)
- A bucket from `ample bucket create` with its credentials passed as encrypted S3_* environment variables
- An Ample account token with servers:write, databases:read, buckets:read

## Exact tested configuration

- template: `python-3.12`
- runtime: `python`
- size: `s-1vcpu-1gb`
- install: `python3 -m pip install --target .ample/python -r requirements.txt`
- start: `PYTHONPATH=.ample/python:${PYTHONPATH:-} python3 run.py`

## Steps

1. **Build and start.** pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template. The server must bind 0.0.0.0 on PORT.
2. **Implement the pattern on PostgreSQL.** The fixture's module implements browser file uploads: content-type and size validation that rejects disallowed files, an object written to a private bucket and a row linking the record to the object key (reject=ok upload=ok linked=ok). Copy the approach into your schema; keep migrations idempotent and run them with --release-command.
3. **Wire object storage.** Create the bucket(s), then pass endpoint, region, bucket and keys as --env values. Use path-style addressing. Keep private data in an unpublished bucket.
4. **Deploy.** Run the synchronous deploy once and read the result (exit 0 live, 1 failed, 2 needs an answer first). Re-running with no change is a no-op.

   ```
   ample deploy . --name <app-name> --public --start "python3 run.py" --env S3_ENDPOINT=... --env S3_REGION=... --env S3_BUCKET=... --env S3_ACCESS_KEY_ID=... --env S3_SECRET_ACCESS_KEY=...
   ```
5. **Verify.** Fetch the live URL and the pattern self-test route(s) (/p/browser-file-uploads) from the example; then run your own checks. On failure read `ample logs <deployment_id> --kind build` then `--kind runtime`.

   ```
   ample logs <deployment_id> --kind build
   ```

## Tested examples

- **FastAPI pattern fixture** (tests/deploy-canaries/fastapi-patterns): Multi-pattern FastAPI app whose browser file uploads module was checked live; the module is under tests/deploy-canaries/_pattern-modules.

## Success checks

- app responds on its public URL (`/` on the live URL, expect ample canary fastapi patterns)
- browser-file-uploads self-test (`/p/browser-file-uploads` on the live URL, expect reject=ok upload=ok linked=ok)


## Cost estimate

Estimated 10.00 USD per month (size prices from pricing.toml at build revision 4558e9477d094f5b47da324b98672824b61ba91b).
- app server x1 `s-1vcpu-1gb`: 5.00 USD
- managed PostgreSQL database x1 `s-1vcpu-1gb`: 5.00 USD

Upper-bound monthly price of the tested sizes. Buckets are allocation-priced per quota and not included.

## Verification evidence

- canary_run on 2026-11-06T00:38:14Z at revision `7360fc06ef21`: FastAPI pattern fixture deployed on Ample (pip install into .ample/python from requirements.txt, then uvicorn from run.py reading PORT on the python-3.12 template); checks passed for browser-file-uploads and configuration-secrets. Pattern proof: content-type and size validation that rejects disallowed files, an object written to a private bucket and a row linking the record to the object key (reject=ok upload=ok linked=ok). (expires 2027-05-05T00:38:14Z)
- canary_run on 2026-11-06T00:41:08Z at revision `7360fc06ef21`: The same FastAPI app deployed with a --release-command migration; the marker it created was readable after activation. (expires 2027-05-05T00:41:08Z)

Last verified: 2026-11-06T00:38:14Z


## Execution binding

MCP tool `ample_deploy` (registry `mcp:ample_deploy`), schema hash `0802c329be823fa0` observed 2026-11-06T06:16:17.558478534+00:00 at revision `4558e9477d09`, binding state `current`, required scopes: servers:write, databases:read, buckets:read.

## Input schema

```json
{
  "additionalProperties": false,
  "properties": {
    "env": {
      "description": "Encrypted environment variables (bucket credentials, secrets)",
      "items": {
        "pattern": "^[A-Z][A-Z0-9_]*=.*$",
        "type": "string"
      },
      "maxItems": 50,
      "type": "array"
    },
    "name": {
      "description": "App name",
      "maxLength": 63,
      "minLength": 1,
      "pattern": "^[a-z0-9-]+$",
      "type": "string"
    },
    "path": {
      "description": "Project directory or ample.toml service",
      "maxLength": 512,
      "minLength": 1,
      "type": "string"
    },
    "release_command": {
      "description": "Migration command run before activation",
      "maxLength": 512,
      "type": "string"
    },
    "start": {
      "description": "Start command (Python apps pass one explicitly)",
      "maxLength": 512,
      "type": "string"
    }
  },
  "required": [
    "env",
    "name",
    "path",
    "start"
  ],
  "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 Form collection (GET /v1/catalog/nodes/workload%3Aform-collection on the api origin; auth: false, approval: false)
- Browse FastAPI (GET /v1/catalog/nodes/stack%3Aframework-fastapi 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)
- Browse Deploy web app (GET /v1/catalog/nodes/intent%3Adeploy-web-app on the api origin; auth: false, approval: false)

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

## About this recipe

Canonical URL: https://ample.computer/recipes/form-collection/fastapi/attachments
Formats: [HTML](https://ample.computer/recipes/form-collection/fastapi/attachments) | [Markdown](https://ample.computer/recipes/form-collection/fastapi/attachments.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Arecipes%3Aform-collection%3Afastapi%3Aattachments)
Recipe ID: `page:recipes:form-collection:fastapi:attachments` | Revision: `r1` | Catalog revision: `cat_eac8c53f36410baa`
Status: verified; runs with one `ample deploy` call (support `verified`, execution `ready`)
Path: [Agent hosting discovery](/discover/discovery) / [Applications and workloads](/discover/workload) / [Scheduling and data](/discover/workload/scheduling-and-data) / [Form collection](/discover/workload/form-collection) / [Host form collection with FastAPI: file attachments](/recipes/form-collection/fastapi/attachments)