🔒 Idempotency in Node.js API using Redis

Adds support for idempotency to an Express.js API using Redis. Idempotency guarantees are for the following scenarios:

1. When a duplicate request is fired sequentially.
2. When duplicate requests are fired parallelly.

Getting started

Pre-requisites

1. Node.js version >= 16
2. (Optional) Access to a remote (MongoDB Atlas) MongoDB database. Point to the desired database by updating the MONGODB_URL in your env file. Pointing to a local MongoDB server is also fine.
3. Redis should be installed. You can refer official installation documentation here.

Installation

1. Run npm install to install the dependencies.
2. Source (or load) the .env file containing your MongoDB URL.

• On macOS, you can do source .env to load environment variables. If it doesn't work, try replacing "source" with "." (for more information, refer this) or load the environment variables directly into the terminal.

3. Run npm start to start the server with nodemon.

How to Use

To see idempotency in action, follow these steps:

1. Once the server is up and running, visit the following URL on your browser to ensure the API is up:

http://localhost:8201

2. Open another tab in your terminal and fire parallel duplicate requests by running the following command in your terminal:

node fire-parallel-requests.js

You would see only one of those 8 parallel duplicate requests will be able to successfully generate a short random slug, rest will fail.

You can visit this to confirm that redirection works:

http://localhost:8201/url/<SLUG>

3. Running the same utility again (without changing the longURL in the request payload) will return the same slug generated in the previous step.

🏁 This clarifies the following:

1. Firing parallel duplicate requests leads to one of them getting hold of an exclusive lock and generating a slug. This slug gets mapped to the provided longURL.
2. Firing the same request(s) again results in the same slug being returned.