The Lessons from enabling search for multitenant applications:

Multitenant search solutions provide search capabilities to any number of tenants who cannot see or share data of any other tenant. Searching often requires content virtualization across different sources where the content can be considered a shared resource. Providing content isolation with search capabilities is the topic of this article.

A search service usually builds an index of the content so that the queries for the content can return results efficiently since the index is far easier and more efficient to lookup than traversing the entire content store. The search service can be considered equivalent to a database service and indeed search can be provided out of box from a database. All the multitenant considerations for database services hold for the search service as well. Each index within a search service has its own schema, which is defined by several customizable fields. Search services, indexes, fields and documents are infrastructure and there is little or no user control.

Some considerations for multitenant applications:

Multitenant applications must effectively distribute resources while preserving privacy between the tenants. A few considerations must be made when designing the architecture for such an application.

-          Tenant Isolation – No tenants must have unauthorized or unwarranted access to the data of other tenants

-          Cloud resource cost – any solution must remain cost-effective.

-          Ease of operation – the impact on the application’s operations and complexity is important.

-          Global Footprint – Applications may need to effectively serve tenants which are distributed across the globe

-          Scalability – applications may need to reconcile between maintaining a sufficiently low level of complexity and scaling to the number and size of workloads.

A uniform scope is assumed where each tenant is a whole instance of an application, but they can handle many smaller scopes. If the service per tenant and index per tenant are not sufficiently small scopes, then the index can be utilized for a finer degree of granularity. A field can be added to an index to make it behave differently to different client endpoints. This helps to achieve separate user accounts, separate permission levels, and even separate applications.

Reference: https://1drv.ms/w/s!Ashlm-Nw-wnWhLMfc6pdJbQZ6XiPWA?e=fBoKcN