# Host Event Registration with Flask: Relational Workflow State

Deploy an event registration built with Flask on Ample using the transactional workflows 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. Verified on Flask: an optimistic version check and an event row written in the same transaction, a stale update rejected, and a history query over the application-owned events (history=2 conflict=rejected). Not separately tested: your domain records, validation rules and concurrency policy; treat the event registration-specific behavior as your application code.

## Summary

- **Framework**: Flask  
- **Workload**: Event registration  
- **Release Status**: published  
- **Support Status**: verified  
- **Execution Status**: ready  
- **Docs Only**: false

## Resource Requirements

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

1. A Flask project that builds and starts with the documented commands (pip install into .ample/python from requirements.txt, then waitress from app.py reading PORT on the python-3.12 template).
2. A PostgreSQL driver reading DATABASE_URL at runtime (auto-provisioned when omitted, or supplied with --env).
3. An Ample account token with servers:write, databases:read.

## Workflow Steps

- **Build and Start**: `pip install into .ample/python from requirements.txt, then waitress from app.py reading PORT on the python-3.12 template. The server must bind 0.0.0.0 on PORT.`
- **Implement the Pattern on PostgreSQL**: Copy the approach into your schema; keep migrations idempotent and run them with --release-command.
- **Deploy**: Run the synchronous deploy once and read the result (exit 0 live, 1 failed, 2 blocked). Re-running with no change is a no-op.
- **Verify**: Fetch the live URL and the pattern self-test route(s) (/p/transactional-workflows) from the example; then run your own checks.

## Examples

- **Flask Pattern Fixture**: Multi-pattern Flask app whose transactional workflows module was checked live; the module is under tests/deploy-canaries/_pattern-modules. Source ref: tests/deploy-canaries/flask-patterns.

## Limitations

1. Verified on the python-3.12 template at s-1vcpu-1gb with the example fixture; other sizes, templates and Flask major versions are not verified.
2. The event registration itself (your domain records, validation rules and concurrency policy) is application code and was not separately tested; the pattern checks are what was verified.
3. Managed PostgreSQL 16 only; extensions, connection limits and backup or restore procedures are not verified; apps and their databases are placed together.

## Success Checks

- App responds on its public URL.
- Transactional-workflows self-test.

## Cost Estimate

- **Currency**: USD  
- **Monthly Amount**: $10.0

### Components

- App server: Size s-1vcpu-1gb, quantity 1.0, monthly amount $5.0.
- Managed PostgreSQL database: Size s-1vcpu-1gb, quantity 1.0, monthly amount $5.0.

### Notes

Always-on monthly price of the tested sizes; apps and databases auto-pause when idle. Buckets are allocation-priced per quota and not included.