问题
We are using Spring Session (backed up with pivotal Gemfire) for our Spring Boot applications running in an Distributed environment.
In such a distributed environment,
does Spring Session ensure that a unique session id is used for new sessions being created across different JVMs ?
回答1:
Just reviewing old SO posts for Spring Session Pivotal GemFire support, so my apologies your question never got answered in a timely manner.
In a nutshell, Spring Session uses the UUID class to generate "unique" Session IDs. For instance, see here, or more generally, here.
NOTE: Spring Session Data Redis support uses/wraps the MapSession class to store Session state in Redis, by default.
There are appears to be a lot of discussion about the effectiveness, or rather uniqueness, of UUID across JVMs in a cluster. This one in particular, though dated, caught my attention as it originated from the Oracle Java community forums.
However, keep in mind that it is your application(s) use of Spring Session that ultimately determines whether Session IDs are unique; i.e. it is not dependent on the number of nodes in a GemFire cluster since individual GemFire nodes are not generating the Session ID (applications using Spring Session are).
Therefore, if only 1 application (probably not likely in the Microservices state of the world) is ever present with Spring Session in use, then the UUIDs are probabilistically guaranteed to be unique. Even then, based on references available, it seems highly unlikely that 2 or more "application" nodes employing Spring Session will ever generate IDs that collide (though, (almost?) anything is possible ;-).
Though, I suppose if it is of paramount concern/importance, following with the beautiful tradition of Spring, it would be a simple matter to extend the GemFireOperationsSessionRepository and override the createSession() method, calling the appropriate GemFireSession constructor to pass the desired Session ID in.
However, in all cases (GemFire, Redis, etc), the Session ID uniqueness problem is agnostic of underlying, backing data store.
Hope this helps...
Cheers!
来源：https://stackoverflow.com/questions/34588960/uniqueness-of-session-id-in-a-distributed-environment