Apply Database Schema Changes for FastAPI

Summary

Apply database schema changes for a FastAPI 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.

Representative Queries

• Apply database schema changes for FastAPI
• Where can I host Apply database schema changes built with FastAPI?
• I need a framework-specific schema migration and rollback procedure; no managed migration service is assumed.

Prerequisites

• 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

Resource Requirements

• primitive:compute
• primitive:postgres

Infrastructure Requirements

• Compute
  Status: verified
  Summary: Apps run in isolated x86_64 Firecracker microVMs that auto-pause when idle and wake on request; sizes are the priced VM sizes.

• Postgres
  Status: verified
  Summary: Managed PostgreSQL 16 runs in its own microVM and is auto-provisioned when an app needs a database and no DATABASE_URL is supplied.

Workflow Steps

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

2. Deploy with the release command
   Ample runs the command before activation; a non-zero exit fails the release.
   Command: ample deploy . --name <app-name> --public --start "python3 run.py" --release-command "python3 migrate.py"

3. Verify the marker through the app
   Serve a route (/migrated) that reads something only the migration creates.

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.
   Command: ample logs <app-name> --kind build

Success Checks

• Migration marker is readable on /migrated path which expects migrated=release-ok.

Limitations

• Verified on the node-22 template at s-1vcpu-1gb; other templates and sizes are not verified by this recipe.
• Region, compliance attestations, and request-duration limits are unknown and not claimed.
• Apps auto-pause when idle and wake on the next request; always-on is an operator setting, not a plan feature.
• Managed PostgreSQL 16 only; extensions, connection limits, and backup or restore procedures are not verified.
• Apps and their managed databases are placed together; cross-node shared databases are unsupported.
• The release command runs once per release on the app VM; there is no separate migration runner or rollback of a partially applied migration.

Cost Estimate

• Currency: USD
• Monthly Amount: $10.00
• Basis: Size prices from pricing.toml (loaded by the API) at build revision 1ac5595375130d45290090e82ed0f554ccd45405-dirty.
• Components:
  • App server: s-1vcpu-1gb, Quantity: 1.0, Monthly Amount: $5.00
  • Managed PostgreSQL database: s-1vcpu-1gb, Quantity: 1.0, Monthly Amount: $5.00
• Note: 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.

Examples

• FastAPI release-command canary
  Description: python3 migrate.py runs before activation against the auto-provisioned managed database.
  Source Reference: tests/deploy-canaries/fastapi-postgres-api.

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