Scalability Scalability is ability of a system to either handle increases in load without impact on the performance of the system, or the ability to be readily enlarged.   There are two methods for improving scalability: scaling vertically (scale up), and scaling horizontally (scale out). To scale vertically, you add more resources such as CPU, memory, and disk to a single system. To scale horizontally, you add more machines to a farm that runs the application and shares the load.   Points to be considered: You may decide to locate logical layers on the same physical tier to reduce the number of servers required while maximizing load sharing and failover capabilities. Consider partitioning data across more than one database server to maximize scale-up opportunities and allow flexible location of data subsets. Consider elastic scalability. Avoid stateful components and subsystems where possible to reduce server affinity. Reduce delays in response and longer completion times. Async communication over sync communication. Implement store-and-forward or cached message-based communication systems that allow requests to be stored when the target system is unavailable, and replayed when it is online. Consider patterns mentioned for Performance attributes.