Multitenancy

Software multitenancy is a software architecture in which a single instance of software runs on a server and serves multiple tenants. Systems designed in such manner are "shared" (rather than "dedicated" or "isolated"). A tenant is a group of users who share a common access with specific privileges to the software instance. With a multitenant architecture, a software application is designed to provide every tenant a dedicated share of the instance - including its data, configuration, user management, tenant individual functionality and non-functional properties. Multitenancy contrasts with multi-instance architectures, where separate software instances operate on behalf of different tenants. Some commentators regard multitenancy as an important feature of cloud computing. Multitenant applications have evolved from—and combine some characteristics of—three types of services: Timesharing: From the 1960s companies rented space and processing power on mainframe computers (time-sharing) to reduce computing expenses. Often they also reused existing applications, with simply a separate entry field on the logon screen to specify a customer-account ID. On the basis of this ID, the mainframe's accountants could charge the individual customers for CPU, memory and disk/tape usage actually incurred. Hosted applications: From the 1990s traditional application service providers (ASPs) hosted (then-existing) applications on behalf of their customers. Depending on the limitation of the underlying application, ASPs were forced to host applications on separate machines (if multiple instances of the applications could not be executed in the same physical machine) or as separate processes. Multitenant applications represent a more mature architecture which enables a similar service with lower operational cost. Web applications: Popular consumer-oriented web applications (such as Hotmail) developed with a single application instance serving all customers.