
Explanation

Update1: VM1 and VM2 only
VM3: Windows Server 2016 West US RG2
Update2: VM4 and VM5 only
VM6: CentOS 7.5 East US RG1
For Linux, the machine must have access to an update repository. The update repository can be private or public.
References:
https://docs.microsoft.com/en-us/azure/automation/automation-update-management