A scaling profile can be changed only when the NAT group is in a shut down state. After the scaling profile is changed and the NAT group is activated (no shutdown), the system tries to allocate necessary memory. If successful, the vISA transitions inservice; if unsuccessful (for example, if there is not enough memory in the system), the NAT group remains in the shut down state.
Without sufficient resources to accommodate the required scaling profile, the vMDA where the vISA resides transitions into a failed state, followed by logs describing the failure:
33 2018/05/28 09:36:30.484 UTC MAJOR: CHASSIS #2001 Base Mda 1/1
"Class MDA Module : failed, reason: Insufficient memory to boot"
36 2018/09/18 14:13:02.426 UTC MAJOR: CHASSIS #2001 Base Mda 1/1
"Class MDA Module : failed, reason: Insufficient mgmt cores to boot"