## Host event registration with Phoenix: relational workflow state

### Summary
Deploy an event registration built with Phoenix 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 Phoenix: 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.

### Representative Queries
- Host event registration with Phoenix: relational workflow state
- Where can I host Event registration built with Phoenix?
- I need a domain record schema, validation rules and concurrency behavior.

### Resource Requirements
- primitive:compute
- primitive:postgres

### Infrastructure 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 Phoenix project that builds and starts with the documented commands (mix deps.get, MIX_ENV=prod mix compile and mix release in the builder, then the release bin script with PHX_SERVER=true on the elixir-1.18 template; PORT, DATABASE_URL and SECRET_KEY_BASE read in config/runtime.exs).
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
1. **Build and start**: `mix deps.get, MIX_ENV=prod mix compile and mix release in the builder, then the release bin script with PHX_SERVER=true on the elixir-1.18 template; PORT, DATABASE_URL and SECRET_KEY_BASE read in config/runtime.exs. The server must bind 0.0.0.0 on PORT.`
2. **Implement the pattern on PostgreSQL**: Copy the approach into your schema; keep migrations idempotent and run them with --release-command.
3. **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: `ample deploy . --name  --public`.
4. **Verify**: Fetch the live URL and the pattern self-test route(s) from the example; then run your own checks: `ample logs  --kind build` then `--kind runtime`.

### Examples
- **Phoenix pattern fixture**: Multi-pattern Phoenix app whose transactional workflows module was checked live; the module is under tests/deploy-canaries/_pattern-modules.

### Success Checks
1. **App responds on its public URL**: `http_get` path: `/`, expect: `ample canary phoenix patterns`.
2. **Transactional-workflows self-test**: `http_get` path: `/p/transactional-workflows`, expect: `tx=ok history=2 conflict=rejected`.

### Limitations
- Verified on the elixir-1.18 template at s-1vcpu-1gb with the example fixture; other sizes, templates and Phoenix major versions are not verified.
- 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.

### Cost Estimate
- **Monthly Amount**: 10.0 USD
- **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

### Evidence Summary
- **Canary run results**: Phoenix pattern fixture deployed on Ample (mix deps.get, MIX_ENV=prod mix compile and mix release in the builder, then the release bin script with PHX_SERVER=true on the elixir-1.18 template; checks passed for transactional-workflows and configuration-secrets).

### Next Actions
1. **Browse the catalog index**: `GET /v1/catalog`
2. **Search published recipes by intent, stack and constraints**: `POST /v1/catalog/search`
3. **Prepare a side-effect-free deployment plan for an authorized project**: `POST /v1/catalog/plan`
4. **Read the existing agent authentication setup**: `GET /mcp/setup`
5. **Browse Event registration**: `GET /v1/catalog/nodes/workload%3Aevent-registration`
6. **Browse Phoenix**: `GET /v1/catalog/nodes/stack%3Aframework-phoenix`
7. **Browse Transactional workflows**: `GET /v1/catalog/nodes/pattern%3Atransactional-workflows`
8. **Browse Deploy web app**: `GET /v1/catalog/nodes/intent%3Adeploy-web-app`