Flask and Celery for Background Tasks

1. Setting Up Flask and Celery

Step 1: Install Dependencies

pip install flask celery redis

Celery requires a message broker. We’ll use Redis, so install it:

sudo apt install redis  # Linux
brew install redis      # macOS

Start the Redis server:

redis-server

2. Configuring Flask with Celery

Step 2: Create `app.py`

from flask import Flask, request, jsonify
from celery import Celery

app = Flask(__name__)
app.config["CELERY_BROKER_URL"] = "redis://localhost:6379/0"
app.config["CELERY_RESULT_BACKEND"] = "redis://localhost:6379/0"

celery = Celery(app.name, broker=app.config["CELERY_BROKER_URL"])
celery.conf.update(app.config)

@celery.task
def long_task(n):
    import time
    time.sleep(n)  # Simulate long-running task
    return f"Task completed after {n} seconds!"

@app.route("/run-task", methods=["POST"])
def run_task():
    data = request.get_json()
    task = long_task.apply_async(args=[data.get("time", 5)])
    return jsonify({"task_id": task.id}), 202

@app.route("/task-status/<task_id>")
def task_status(task_id):
    task = long_task.AsyncResult(task_id)
    return jsonify({"status": task.status, "result": task.result})

if __name__ == "__main__":
    app.run(debug=True)

3. Running Celery Workers

Step 3: Start Flask and Celery

1️⃣ Run Flask:

python app.py

2️⃣ Start the Celery Worker:

celery -A app.celery worker --loglevel=info

4. Testing Background Task Execution

Step 4: Trigger a Background Task

Send a request using Postman or cURL:

curl -X POST http://127.0.0.1:5000/run-task -H "Content-Type: application/json" -d '{"time": 10}'

This will return a task ID:

{"task_id": "d4f3b9c7-XXXX-XXXX-XXXX-XXXXXXXXXXXX"}

5. Deploying Flask with Celery

Step 5: Running Celery in Production

For production, use Celery with a process manager like Supervisor to keep it running:

sudo apt install supervisor

Then, create a config file for Celery:

[program:celery]
command=celery -A app.celery worker --loglevel=info
autostart=true
autorestart=true
stderr_logfile=/var/log/celery.err.log
stdout_logfile=/var/log/celery.out.log

Conclusion

In this guide, we covered:

✅ Installing and setting up Celery with Flask.
✅ Running background tasks without blocking Flask.
✅ Using Redis as a message broker.
✅ Deploying Celery for production-ready applications.

Now, your Flask app can efficiently handle long-running tasks like email notifications, data processing, and more! 🚀

PYTHON FLASK