Would you rather maintain a user session for a web application using load balancer affinity or by storing it in the database?

In this question, the interviewer aims to evaluate your understanding of two methods for maintaining user sessions in a web application: affinity on a load balancer and database persistence. They want you to compare these approaches and share your preferred choice along with your reasoning. User session persistence is crucial for web applications as it helps keep track of the user's state across multiple requests. Session affinity on a load balancer, often referred to as sticky sessions, ensures that all requests from a particular user are routed to the same server where their session was initially created. In contrast, database persistence involves saving session information in a database that can be accessed by any server. To answer this question effectively: Explain both methods for persisting user sessions. Discuss the advantages and disadvantages of each approach. Clearly indicate your preference for one method over the other, along with your justification.

I think both approaches have their benefits and should be chosen based on the specific needs of the application. Using client affinity on a load balancer with sticky sessions can be beneficial as it may lead to quicker response times; once a session starts, subsequent requests can be swiftly routed to the server managing the session, thus avoiding delays associated with database lookups. However, if the server fails, the session information will be lost unless it is saved on another server, and this method could lead to an uneven distribution of load. Conversely, storing sessions in a database guarantees that session data can be recovered by a backup server in the event of a server crash. Nevertheless, this approach might introduce some performance overhead due to the read and write operations required for each request to the database. Considering these factors, if the application experiences frequent access and involves substantial session data, I would prefer using a database for session persistence for enhanced durability and reliability. However, if immediate performance is crucial for the application, then session affinity on the load balancer might be the better choice.

My choice between using session persistence through affinity on a load balancer or in a database would depend on the particular requirements of the web application in question. If the primary goal is to balance the load by distributing user requests across several servers to maximize resource utilization and avoid any single server becoming overloaded, then maintaining persistent sessions via a load balancer might be more advantageous, as it eliminates the need to constantly retrieve and update session data from the database. In contrast, for web applications where the data is essential for the service's functionality and integrity, and where it’s vital to prevent any data loss in the event of server failures, I would likely choose database persistence. Nevertheless, it is crucial to take into account factors like the size of the session data, user behavior, and the characteristics of the datacenter. At times, a hybrid strategy that combines both methods could be the most effective solution.