# Procfile

Railpack automatically detects and uses `Procfile` configuration files to
determine how your application should start. This is compatible with
Heroku-style Procfiles and provides a simple way to specify different process
types for your application.
**Note:** Procfiles are deprecated and natively setting the start command with
  `RAILPACK_START_CMD` or in the `railpack.json` config file is recommended.

## Detection

Railpack will automatically detect a `Procfile` in your project root directory.
No additional configuration is required - if a `Procfile` exists, Railpack will
use it to set the container start command.

## Format

The `Procfile` uses a YAML-style format where each line defines a process type
and its associated command:

```yaml
web: gunicorn --bind 0.0.0.0:3333 main:app
worker: celery worker -A myapp.celery
scheduler: celery beat -A myapp.celery
```

## Process Type Priority

Railpack prioritizes process types in the following order:

1. **web** - Highest priority, typically used for HTTP servers
2. **worker** - Second priority, typically used for background job processors
3. **Any other process type** - If neither `web` nor `worker` are defined,
   Railpack will use the first available process type

This priority system ensures that web servers are preferred for containerized
deployments, while still supporting applications that only define worker
processes or custom process types like `scheduler`, `urgentWorker`, or `api`.

## Examples

### Web Application

```yaml
web: node server.js
```

### Background Worker

```yaml
worker: python worker.py
```

### Multiple Process Types

```yaml
web: gunicorn app:application
worker: celery worker -A app.celery
scheduler: celery beat -A app.celery
```

In this example, Railpack will use the `web` command as the container start
command.

### Custom Process Types

```yaml
api: ./bin/api-server
urgentWorker: python urgent_tasks.py
```

If no `web` or `worker` process types are defined, Railpack will use the first
available process type (in this case, `api`).

## Integration with Other Configuration

The Procfile start command can be overridden by:

- Setting `RAILPACK_START_CMD` environment variable
- Defining `deploy.startCommand` in your [railpack.json config
  file](/config/file)

The priority order is:

1. `RAILPACK_START_CMD` environment variable (highest priority)
2. `deploy.startCommand` in railpack.json
3. Procfile process types (web → worker → other)
4. Provider-specific defaults (lowest priority)