According to the definition available online is "Multi-tenancy is an architecture in which a single instance of a software application serves multiple customers". The term "software multitenancy" refers to a software architecture in which a single instance of software runs on a server and serves multiple tenants. Systems designed in such manner are often called shared (in contrast to 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.
Types of multi-tenant architecture:
There are three main multi-tenancy model types, all with varying levels of complexity and costs. A single, shared database schema is a multi-tenancy model with a multi-tenant database. This is the simplest form out of the three and is a relatively low cost for tenants because of the use of shared resources. This form uses a single application and database instance to host tenants and store data. Using a single, shared database schema allows for easier scaling; however, operational costs can be higher.
Another multi-tenant architecture includes the use of a single database with multiple schemas. This tenant system uses a single application instance with individual databases for each tenant. In addition, this architecture has a higher cost with more overhead with each database. It is a valuable architecture when data from different tenants need to be treated differently -- such as if they had to go through different geographic regulations.
The third type of multi-tenant architecture hosts data in multiple databases. This model is relatively complex in terms of management and maintenance, but tenants can be separated by a chosen criterion.
In cloud computing, the meaning of multi-tenant architecture has broadened because of new service models that take advantage of virtualization and remote access. A software-as-a-service (SaaS) provider, for example, can run one instance of its application on one instance of a database and provide web access to multiple customers.
In such a scenario, each tenant's data is isolated and remains invisible to other tenants. Multi-tenancy can also be implemented in multi-tier systems such as an SAP system.
