Azure alert on multipel subscriptions

Hi JanLD8850 

That's because metrics has that restriction, alerts through metrics are easier to setup but hard to manage on time, because you'll need several rules which will do the same for different scopes. 

You should take a look to azure monitoring with log analytics workspace, this way you can build your own alert rules through KQL, if you need to monitor cpu for 100 vm's you can setup a single rule for all virtual machines in that directory, or just filtered for the scope you need.

Here's an example:

InsightsMetrics 
| where Origin == "vm.azm.ms" 
| where Namespace == "Processor" and Name == "UtilizationPercentage" 
| summarize CPUPercentageAverage = avg(Val) by bin(TimeGenerated, 15m), Computer, _ResourceId 

Log search alert rules

And another more complex rule:

{
    let RuleGroupTags = dynamic(['Linux']);
    Perf | where ObjectName == 'Processor' and CounterName == '% Idle Time' and (InstanceName in ('_Total,'total'))
    | extend CpuUtilisation = (100 - CounterValue)   
    | join kind=inner hint.remote=left (arg("").Resources
        | where type =~ 'Microsoft.Compute/virtualMachines'
    | project _ResourceId=tolower(id), tags) on _ResourceId
    | project-away _ResourceId1
    | where  (tostring(tags.monitorRuleGroup) in (RuleGroupTags)) 
}

Query that filters virtual machines that need to be monitored

Regards,