Utilizing Python, FastAPI, and Redis Queue for Background Job Processing | Python | Message Queue

Background job processing is a common requirement in many web applications. It allows you to execute long-running tasks in the background without blocking the main thread or the user’s request. In this tutorial, we will explore how to implement background job processing using Python, FastAPI, and Redis Queue (RQ) as the message queue.

What is Redis Queue (RQ)?
Redis Queue (RQ) is a simple Python library for queueing jobs and processing them in the background with Redis as the message broker. It is built on top of Redis and provides a simple API for creating, enqueuing, and processing jobs.

Prerequisites
Before getting started, make sure you have the following installed on your machine:

1. Python 3.x
2. FastAPI
3. Redis server
4. Redis Queue (RQ) library

Setting up Redis
First, you need to have Redis installed and running on your machine. You can download Redis from https://redis.io/download and follow the installation instructions for your operating system.

Once Redis is installed, start the Redis server by running the following command in your terminal:

redis-server

Setting up FastAPI
FastAPI is a modern web framework for building APIs with Python. You can install FastAPI using pip:

pip install fastapi

Creating a FastAPI application
Now, let’s create a simple FastAPI application that will enqueue and process background jobs using Redis Queue.

Create a new Python file, app.py, and add the following code:

from fastapi import FastAPI
import rq
from rq import Queue
from redis import Redis

app = FastAPI()

# Connect to Redis
redis_conn = Redis()
queue = Queue(connection=redis_conn)

# Background job function
def process_job(job_id):
    print(f"Processing job {job_id}")

# Route to enqueue a job
@app.post("/enqueue-job/{job_id}")
async def enqueue_job(job_id: int):
    job = queue.enqueue(process_job, job_id)
    return {"message": f"Job enqueued with id {job.id}"}

In this code snippet, we have created a FastAPI application with a route /enqueue-job/{job_id} that accepts a job ID as a parameter and enqueues a background job using Redis Queue.

Processing background jobs
To process the enqueued jobs, we need to create a separate worker process that listens for and processes the jobs in the queue.

Create a new Python file, worker.py, and add the following code:

import os
import rq
from redis import Redis

# Connect to Redis
redis_conn = Redis()
queue = rq.Queue(connection=redis_conn)

# Worker process
def worker():
    with rq.Connection(redis_conn):
        worker = rq.Worker([queue])
        worker.work()

if __name__ == "__main__":
    worker()

This code snippet creates a worker process that listens for jobs in the queue and processes them using the function process_job defined in app.py.

Running the application
To run the FastAPI application and start enqueueing jobs, run the following command in your terminal:

uvicorn app:app --reload

Open a new terminal window and start the worker process by running the following command:

python worker.py

Now, you can enqueue jobs by sending a POST request to http://localhost:8000/enqueue-job/{job_id}. The worker process will process the enqueued jobs in the background.

Conclusion
In this tutorial, we learned how to implement background job processing using Python, FastAPI, and Redis Queue. By leveraging message queues like Redis Queue, you can efficiently handle long-running tasks in your web applications without affecting performance or user experience. Experiment with different types of jobs and explore more advanced features of Redis Queue to build robust and scalable applications.