What is an SPN and why should I use one in Windows?Kerberos with Service Principal Name (SPN) is a Microsoft document.
The instance service has a service principal name.A service instance is associated with a service logon account with the use of SPNs.If the client doesn't have the account name, the application can request that the service verify it.
If you install multiple instances of a service on computers throughout a forest, each instance must have its own SPN.If there are multiple names that clients might use, a service instance can have multiple SPNs.The name of the host computer on which the service instance is running will always be included in an SPN.See name formats for unique SPNs for more information.
The account object that the service instance uses to log on must be registered with the SPN.Only one account can be used for a given SPN.When an instance of the service is installed, a service installer specifies the logon account.The SPNs are written as a property of the account object in Active Directory.The service instance's logon account must be changed if the SPNs are to be re-registered.How a Service Registers its SPNs can be found here.
When a client wants to connect to a service, it needs to locate an instance of the service and create an SPN for it.How Clients Compose a Service's SPN can be found here.