---
title: "How to set build and start commands for a FastAPI app on Ample"
description: "Configure build and start for a FastAPI app on Ample."
canonical_url: "https://ample.computer/guides/fastapi/build-and-start"
last_updated: "2026-11-05"
---

# How to set build and start commands for a FastAPI app on Ample

Configure build and start for a FastAPI app on Ample. Start uvicorn from a small run.py that reads PORT; pass --start "python3 run.py" (or answer the start question `ample plan` asks). Ample detects the runtime, installs dependencies, runs the build when present and starts the app on the python-3.12 template behind a public HTTPS URL.

## Infrastructure requirements

- [Compute](/discover/primitive/compute): verified (Apps run in isolated x86_64 Firecracker microVMs; sizes are the priced VM sizes.)

## Prerequisites

- A requirements.txt (or pyproject) and a start command that reads PORT and binds 0.0.0.0
- An Ample account token with servers:write

## 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. **Make the start command bind correctly.** Start uvicorn from a small run.py that reads PORT; pass --start "python3 run.py" (or answer the start question `ample plan` asks).
2. **Deploy.** Run the existing synchronous deploy once from the project directory and read the result. Exit 0 is live, 1 is failed, 2 needs an answer first (a preflight question). Re-running with no change is a content-addressed no-op.

   ```
   ample deploy . --name <app-name> --public --format json --start "python3 run.py"
   ```
3. **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

- **fastapi-basic canary** (tests/deploy-canaries/fastapi-basic): FastAPI app started with uvicorn.

## Success checks

- page or root route responds (`/` on the live URL, expect ample canary fastapi basic)


## Cost estimate

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

Upper-bound monthly price of the tested sizes. Plan quotas and budgets apply.

## Verification evidence

- canary_run on 2026-11-05T22:38:23Z at revision `da3e37255e5a`: FastAPI app installed with pip into .ample/python and started with uvicorn on python-3.12; / and /health served correctly. (expires 2027-05-04T22:38:23Z)

Last verified: 2026-11-05T22:38:23Z


## Execution binding

MCP tool `ample_deploy` (registry `mcp:ample_deploy`), schema hash `0802c329be823fa0` observed 2026-11-06T06:16:19.461833707+00:00 at revision `4558e9477d09`, binding state `current`, required scopes: servers:write.

## Input schema

```json
{
  "additionalProperties": false,
  "properties": {
    "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": [
    "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 FastAPI (GET /v1/catalog/nodes/stack%3Aframework-fastapi on the api origin; auth: false, approval: false)
- Browse Configure deployment (GET /v1/catalog/nodes/intent%3Aconfigure-deployment on the api origin; auth: false, approval: false)
- Browse Public web service (GET /v1/catalog/nodes/pattern%3Apublic-web-service 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/guides/fastapi/build-and-start
Formats: [HTML](https://ample.computer/guides/fastapi/build-and-start) | [Markdown](https://ample.computer/guides/fastapi/build-and-start.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Aguides%3Afastapi%3Abuild-and-start)
Recipe ID: `page:guides:fastapi:build-and-start` | Revision: `r1` | Catalog revision: `cat_eac8c53f36410baa`
Status: verified; runs with one `ample deploy` call (support `verified`, execution `ready`)
Path: [Agent hosting discovery](/discover/discovery) / [Frameworks and execution targets](/discover/stack) / [Frameworks](/discover/stack/frameworks) / [FastAPI](/discover/stack/framework-fastapi) / [Configure build and start for FastAPI](/guides/fastapi/build-and-start)