The Stateless Processes

When it comes to software development, managing how your application processes data and requests is key to ensuring it operates smoothly and efficiently. But how do you handle these processes effectively? The answer lies in designing your application to run as one or more stateless processes. This approach ensures that your app can handle requests independently, without relying on stored data from previous interactions, leading to more scalable and robust applications. Let's dive deeper into what it means to run your app with stateless processes and why it's a game-changer for developers.

What Are Stateless Processes?

Imagine your app as a factory where workers (processes) handle tasks (requests). In a stateless setup, each worker starts a task without relying on what happened before. They don’t remember past tasks (state/session information) and don’t keep any secrets (share nothing).

Why Stateless?

Flexibility: Your app can run anywhere, from a single developer's laptop to a massive cloud-based system, without worrying about the specific environment.
Scalability: Since each process is independent, it's easier to add more processes to handle increased load.

"Designing applications with stateless processes is like giving each task a fresh start, free from the baggage of the past. This strategy boosts flexibility and scalability, ensuring an app's smooth operation and easy growth, without being hindered by history."

Storing Data the Right Way

Since our processes don’t remember anything, where do we store important information? Here’s where stateful backing services, like databases (DB), come into play. These are the shelves where workers store their tools and materials. Processes can temporarily hold onto information, like caching a file for a quick task, but any long-term storage needs to happen outside, in a DB.

The Temporary Nature of Local State

In a 12-factor app, there’s no expectation that something stored temporarily will be there later. It’s like knowing that anything left on your desk at work might be gone the next day if it’s not properly saved somewhere secure.

Consider a scenario where your application is tasked with handling a large image file. The process would typically involve downloading the image to a temporary storage location, either in memory or on disk. Following this, the app would perform various processing tasks on the image, such as resizing or applying filters. Finally, the processed image would be saved in a database for long-term storage and access. This sequence of actions exemplifies how an app can manage data processing efficiently, without the need to retain state information between steps.

This way, even if the process restarts or another process takes over, the important result is safely stored.

Handling Assets Correctly

For web apps, assets (like CSS and JavaScript files) should be prepared before your app starts running. Tools like Webpack compile these assets during the build stage, ensuring your app doesn’t waste time compiling them on the fly.

Moving Beyond Sticky Sessions

Sticky sessions are like giving a customer a personal assistant who remembers everything about them. It sounds nice but goes against the stateless principle. Instead, use external services like Memcached or Redis to remember session data. This way, any process can handle any request without needing a personal history with the user.

In the context of managing user sessions within an app, consider the following workflow: A user logs into the application. Instead of storing their session data within the application process itself, it's saved in an external service like Redis. This approach means that any process within the app's architecture can access the session data from Redis to handle the user's subsequent requests. This setup ensures users have a seamless experience across different interactions with the app, as no single process is burdened with the task of "remembering" the user's session information, thus adhering to the stateless design principle.

This visual would help underline the beauty of a stateless architecture, where every component plays its role without holding onto unnecessary information, leading to a smoother, more scalable application.