Which is the best session persistence option?

You require high availability for HTTP sessions in a web application. In addition, you have
the following constraints: • There is little free memory on the machines hosting the cluster. •
HA must be guaranteed even when multiple machines fall simultaneously. • You are not
allowed to update the production databases schema. Which is the best session persistence
option?

A.
Whole –server migration

B.
In-memory replication

C.
Database persistence

D.
File persistence