## The short version

Apply database schema changes for a Flask app on Ample with a release command. `python3 migrate.py` runs against the injected DATABASE_URL before the new release goes live, and the release fails instead of activating if the migration fails.

## INFRASTRUCTURE

## 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.)
- [Postgres](/content/discover/primitive/postgres/index.html): 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

## Before you start

- A migration command that reads DATABASE_URL and exits non-zero on failure
- A PostgreSQL database (supplied or managed)
- An Ample account token with servers:write and databases:read

## STEP BY STEP

## How to do it

1. 1

### Write an idempotent migration

Create tables and markers with IF NOT EXISTS or a migration framework so a re-run is safe.

2. 2

### Deploy with the release command

Ample runs the command before activation; a non-zero exit fails the release.

```
ample deploy . --name <app-name> --public --start "python3 run.py" --release-command "python3 migrate.py"
```

3. 3

### Verify the marker through the app

Serve a route (/migrated) that reads something only the migration creates.

4. 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
```

## EXAMPLES

## Tested examples

- **Flask release-command canary** (`tests/deploy-canaries/flask-postgres-app`): python3 migrate.py runs before activation against the auto-provisioned managed database.

## SUCCESS CHECKS

## How to know it worked

- migration marker is readable (`/migrated` on the live URL, expect migrated=release-ok)

## COST

## Cost estimate

Estimated 10.00 USD per month (size prices from pricing.toml at build revision ca0b484a7a9957c573a88d3a32dc603c3c10135a).

- 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. Plan quotas and budgets apply.

## EVIDENCE

## Verification evidence

- canary_run on 2026-09-20T01:42:25Z at revision `199ff1dfd52683832ae75d3f98b53a7a4bff7f96 (CLI e3181f5)`: The same Flask app deployed with --release-command python3 migrate.py; /migrated reported the migration marker. (expires 2027-03-19T01:42:25Z)

## EXECUTION

## 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, databases:read.

## NEXT ACTIONS

## 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 Flask (`GET /v1/catalog/nodes/stack%3Aframework-flask` on the api origin; authentication not required, approval not required)
- Browse Configure deployment (`GET /v1/catalog/nodes/intent%3Aconfigure-deployment` on the api origin; authentication not required, approval not required)
- Browse Transactional workflows (`GET /v1/catalog/nodes/pattern%3Atransactional-workflows` on the api origin; authentication not required, approval not required)

## ABOUT THIS RECIPE

## Identifiers and status

Recipe `page:guides:flask:schema-changes`. Revision r1.

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

Formats: [HTML](/content/guides/flask/schema-changes/index.html) | [Markdown](/content/guides/flask/schema-changes.md) | [JSON contract](https://api.ample.computer/v1/catalog/recipes/page%3Aguides%3Aflask%3Aschema-changes)