Identity management appliance or SSO or PSC
The identity management appliance or vSphere 5.5 SSO or vSphere 6.0 PSC provides Single Sign-On (SSO) capabilities that allow connectivity to Active Directory (AD) or Open LDAP-compatible directory services.
Identity management appliance
This is a preconfigured virtual appliance that serves as the heart of the SSO system with limited capabilities released specifically for the vRealize Automation product. It serves all authentication requests and handles multiple identity sources and uses a routing layer to route requests to an appropriate subsystem (a configuration or authentication interface). It is important to note that an IDM appliance is recommended for small-scale deployments. If your design demands high availability, you could use a vSphere feature such as HA and FT since the IDM appliance does not have native capability to cluster or join with the existing SSO deployments.
vSphere 5.5 SSO
vSphere 5.5 SSO is available as a Windows-based as well as a Linux-based appliance and can be added to an existing SSO domain. If your design demands an SSO configuration to be highly available behind a load balancer, you are limited to using only a Windows version of SSO, but be aware that it supports active/passive failover mode.
vSphere 6.0 PSC
Since the release of vSphere 6, the SSO configuration has been built into Platform Service Controller (PSC) that is available in both Linux and Windows-based flavor. If your design demands an SSO configuration to be highly available behind a load balancer, you have the flexibility to choose between both Linux and Windows:
