A zero downtime upgrade procedure is initiated that upgrades a first version of software executing on a source system comprising at least one source server to a second version of software executing on a target system comprising at least one target server. The source system initially starts operating in a read-write mode. Thereafter, concurrent with the operation of the source system, operation of the target system is initiated in a read-only mode. Operations of the source system are then ceased by ramping down activities of the source system. Upon cessation of operation of the source system, operation of the target system is initiated in a read-write mode.