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 fail simultaneously. "¢ You are not allowed to update the production databases schema. Which is the best session persistence option? 

Answer options:

A. Database persistence
B. File persistence
C. In-memory replication
D. Whole-server migration

C