The OpenStack Identity service, known as Keystone, provides services for authenticating and managing user accounts and role information for our OpenStack cloud environment. It is a crucial service that underpins the authentication and verification between all of our OpenStack cloud services and is the first service that needs to be installed within an OpenStack environment. The OpenStack Identity service authenticates users and tenants by sending a validated authorization token between all OpenStack services. This token is used for authentication and verification so that you can use that service, such as OpenStack Storage and Compute. Therefore, configuration of the OpenStack Identity service must be completed first, consisting of creating appropriate roles for users and services, tenants, the user accounts, and the service API endpoints that make up our cloud infrastructure.
In Keystone, we have the concepts of tenants, roles and users. A tenant is like a project and has resources such as users, images, and instances, as well as networks in it that are only known to that particular project. A user can belong to one or more tenants and is able to switch between these projects to gain access to those resources. Users within a tenant can have various roles assigned. In the most basic scenario, a user can be assigned either the role of admin or just be a member. When a user has admin privileges within a tenant, they are able to utilize features that can affect the tenant (such as modifying external networks), whereas a normal user is assigned the member role, which is generally assigned to perform user-related roles, such as spinning up instances, creating volumes, and creating tenant only networks.