Chapter 8 Quality attributes and sizing of the dXp Reliability Requirements Reliability ensures that the system consistently performs the specified functionality and recovers from failure. Given below are key reliability requirements: • The system should consistently provide expected behavior. • If any of the back-end systems or service fails, the digital application will not fail. The application should be able to gracefully recover from the failure. • The system will handle the re-initiation of operations that lead to an inconsistent state. For instance, the system will prevent double clicking of the “checkout” function before the first checkout operation is completed. • The system handles unexpected and error scenarios such as long- running transactions, failed transactions, network errors, outage of back-end systems, and such. The system logs the issues and gracefully rollbacks and shows friendly error messages in such scenarios. • The infrastructure should be designed to be fault tolerant. Scalability Requirements Scalability ensures that the application scales well for the larger workload, with acceptable performance. The following are the main scalability requirements: • For on-premise deployments, the application should be deployed as a multinode cluster. • The system should be able to handle increased user load and data load, and should be able to handle future data growth. • Horizontal and vertical scaling should be supported by the system. • If any of the cluster nodes goes down (web server node, application server node, or database server node), the system should be able to load balance and seamlessly switch all the traffic to other nodes to provide the expected response. • The system should provide response within an acceptable time period, even during peak traffic. 219