Dealing with Stateful Communications
Explore strategies to handle stateful communications in Node.js applications that require session persistence. Understand the challenges of scaling stateful apps with clustering and load balancing. Learn how to use shared datastores and sticky load balancing techniques to maintain session state, enabling you to build scalable, reliable Node.js systems.
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The cluster module doesn’t work well with stateful communications where the application state isn’t shared between the various instances. This is because different requests belonging to the same stateful session may potentially be handled by a different instance of the application. This isn’t a problem limited only to the cluster module, but, in general, it applies to any kind of stateless, load-balancing algorithm. Consider, for example, the situation described in the illustration below.
The user John initially sends a request to our application to authenticate himself, but the result of the operation is registered locally (for example, in memory), so only the instance of the application that receives the authentication request (Instance A) knows that John is successfully authenticated. When John sends a new request, the load balancer might forward it to a different instance of the application, which actually doesn’t possess the authentication details of John, therefore ...