...
Stateful (active) Tasks := {T1, T2, T3}
Standby Tasks Replicas := {S1, S2, S3}1
Instances := {I1, I2}
Initial State
...
Stateful (active) Tasks := {T1, T2, T3, T4}
Standby Tasks Replicas := {S1, S2, S3, S4} 1
Instances := {I1, I2, I3}
The standby tasks in this scenario are assumed to be in sync with the active tasks, that is, caught up and within acceptable_recovery_lag.
...
Stateful (active) Tasks := {T1, T2, T3, T4}
Standby Tasks Replicas := {S1, S2, S3, S4} 1
Instances := {I1, I2, I3}
In this scenario, the standby tasks are lagging the active tasks by some nontrivial amount, that is, by more than the acceptable_recovery_lag.
...