---
title: "Connect Postgres for FastAPI"
description: "Connect a FastAPI app to PostgreSQL on Ample."
canonical_url: "https://ample.computer/guides/fastapi/database-connection"
last_updated: "2026-09-20"
---

# Connect Postgres for FastAPI

Canonical URL: https://ample.computer/guides/fastapi/database-connection
Formats: [HTML](https://ample.computer/guides/fastapi/database-connection) | [Markdown](https://ample.computer/guides/fastapi/database-connection.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Aguides%3Afastapi%3Adatabase-connection)
Recipe ID: `page:guides:fastapi:database-connection` | Revision: `r1` | Catalog revision: `cat_f13ab9a494120b5e`

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

## Summary

Connect a FastAPI app to PostgreSQL on Ample. Read DATABASE_URL at runtime with psycopg: when you supply one with --env it is delivered encrypted and takes precedence; when you supply none and the app needs PostgreSQL, Ample auto-provisions a managed PostgreSQL 16 database and injects its connection string.

Path: [Agent hosting discovery](/discover/discovery) / [Frameworks and execution targets](/discover/stack) / [Frameworks](/discover/stack/frameworks) / [FastAPI](/discover/stack/framework-fastapi) / [Connect Postgres for FastAPI](/guides/fastapi/database-connection)

## 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.)
- [Postgres](/discover/primitive/postgres): verified (Managed PostgreSQL 16 runs in its own microVM and is auto-provisioned when an app needs a database and no DATABASE_URL is supplied.)

## Prerequisites

- psycopg reading the DATABASE_URL environment variable at runtime
- Either a production DATABASE_URL to pass with --env, or nothing (auto-provision)
- An Ample account token with servers:write and databases: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. **Read the URL at runtime.** Open connections from the DATABASE_URL environment variable inside the app; never commit credentials and never connect at build time.
2. **Choose the source of the database.** Pass --env DATABASE_URL=... for an existing database, or omit it to let Ample provision a managed one on first deploy and reuse it on redeploys.

   ```
   ample deploy . --name <app-name> --public --start "python3 run.py"
   ```
3. **Test the connection through the app.** Expose a route (/items) that runs a trivial query and returns postgres=ok.
4. **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 + PostgreSQL canary** (tests/deploy-canaries/fastapi-postgres-api): Auto-provisioned managed database with a real query.

## Success checks

- database route reports a live connection (`/items` on the live URL, expect postgres=ok)


## Cost estimate

Estimated 10.00 USD per month (size prices from pricing.toml at build revision 515b7316fc6e5a81679407ae0c811146ceb2c5c7).
- app server x1 `s-1vcpu-1gb`: 5.00 USD
- managed PostgreSQL database x1 `s-1vcpu-1gb`: 5.00 USD

Apps and managed databases auto-pause when idle; the estimate is the always-on monthly price of the tested sizes. Plan quotas and budgets apply.

## Verification evidence

- canary_run on 2026-09-20T01:42:25Z at revision `199ff1dfd52683832ae75d3f98b53a7a4bff7f96 (CLI e3181f5)`: FastAPI REST API using psycopg with no DATABASE_URL supplied: Ample auto-provisioned a managed PostgreSQL 16 database and /items reported postgres=ok after a real insert and count. (expires 2027-03-19T01:42:25Z)
- canary_run on 2026-09-19T23:55:33Z at revision `1764076-tls-account-903d345`: Node app needing PostgreSQL with no DATABASE_URL: a managed database was auto-provisioned and /db reported postgres=ok. (expires 2027-03-18T23:55:33Z)

Last verified: 2026-09-20T01:42:25Z


## 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, databases:read.

## Input schema

```json
{
  "additionalProperties": false,
  "properties": {
    "env": {
      "description": "Encrypted environment variables as KEY=value; secret values are never stored in ample.toml",
      "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": [
    "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 Connect app to database (GET /v1/catalog/nodes/intent%3Aconnect-app-to-database on the api origin; auth: false, approval: false)
- Browse Relational records (GET /v1/catalog/nodes/pattern%3Arelational-records on the api origin; auth: false, approval: false)

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