# Deploying Celery on AWS Elastic Beanstalk

AWS Elastic Beanstalk (EB) makes it easy to deploy, manage, and scale applications. Running background tasks with Celery on EB typically involves one of two architectures: running the worker alongside the web server or using a dedicated worker environment.

## Approach 1: The `Procfile` Method (Recommended for Amazon Linux 2/2023)

Modern Elastic Beanstalk platforms (Amazon Linux 2 and newer) use a `Procfile` to manage processes. This is the simplest way to run a Celery worker alongside your web application.

### 1. Create a `Procfile`

Create a file named `Procfile` (no extension) in the root of your project source code.

```text
web: gunicorn myproject.wsgi:application
worker: celery -A myproject worker --loglevel=INFO
beat: celery -A myproject beat --loglevel=INFO
```

*   **web**: Your main application server (e.g., Gunicorn for Django).
*   **worker**: The Celery worker process.
*   **beat**: (Optional) The Celery Beat scheduler. *Note: Only run one Beat instance per deployment to avoid duplicate tasks.*

### 2. How it Works

Elastic Beanstalk reads this file and uses the process manager (usually Systemd) to keep these processes running. If the worker crashes, EB restarts it. Logs are aggregated automatically.

## Approach 2: Dedicated Worker Tier

For high-load applications, you might want to separate your web instances from your worker instances. EB offers a specific "Worker Environment" tier.

### The SQS Daemon (`sqsd`) vs. Celery

By default, the EB Worker Tier runs a daemon called `sqsd`. It polls an SQS queue and sends an **HTTP POST** request to your application (e.g., `/tasks/process`) with the message body.

*   **If you use `sqsd`**: You don't strictly need Celery; you just need an endpoint in your Flask/Django app to handle the POST request.
*   **If you want standard Celery**: You can disable `sqsd` and use the `Procfile` method within the Worker Tier to run `celery worker` consuming from SQS (or Redis).

## Configuration Tips

### 1. Environment Variables

You must configure your broker URL via the EB Console or CLI.

```bash
eb setenv CELERY_BROKER_URL="redis://my-elasticache-endpoint:6379/0"
```

### 2. Installing System Dependencies

If your tasks require system libraries (like `libpq-dev` or `Pillow` dependencies), use `.ebextensions`.

Create `.ebextensions/01_packages.config`:

```yaml
packages:
  yum:
    postgresql-devel: []
    libjpeg-turbo-devel: []
```

### 3. Deployment Hooks (Advanced)

If you need to run scripts *before* the worker starts (e.g., to clean up PID files), use `.platform/hooks`.

File: `.platform/hooks/prebuild/01_cleanup.sh`

```bash
#!/bin/bash
rm -f celerybeat.pid
```

[[programming/python/celery]]