node_cpu_seconds_total gives you a separate metric for each CPU, so with an
8 vCPU VM you'll get 8 alerts (if they're all under 20%)
You're saying that you're happy with all these alerts, but want to suppress
them where the VM has only one vCPU? In that case:
count by (instance) (node_cpu_seconds_total{mode="idle"})
will give you the number of CPUs per instance, and hence you can modify
your alert to something like
expr: ( ......... unless on (instance) count by (instance)
(node_cpu_seconds_total{mode="idle"} == 1)
which would give something like:
(
(100 - (rate(node_cpu_seconds_total{mode="idle"}[30m]) * 100) < 20)
unless on (instance)
count by (instance) (node_cpu_seconds_total{mode="idle"} == 1)
)
* on (instance) group_left (nodename)
node_uname_info{nodename=~".+"}
Aside 1: personally I like to leave percentages as fractions. You can
change these to percentages in alerts using humanizePercentage
<https://prometheus.io/docs/prometheus/latest/configuration/template_reference/#numbers>
Aside 2: It might be better to aggregate all the CPUs usage for an
instance. Otherwise, if you have 8 mostly-idle CPUs, but each CPU in turn
has a short burst of activity, you'll get no alerts. Do do this, you
should use sum over rate
<https://www.robustperception.io/rate-then-sum-never-sum-then-rate/>, not
rate over sum.
On Saturday 22 June 2024 at 17:01:58 UTC+1 mel wrote:
> I have this CPU underutilized alert for virtual machines.
>
> expr: '(100 - (rate(node_cpu_seconds_total{mode="idle"}[30m]) * 100) < 20)
> * on(instance) group_left (nodename) node_uname_info{nodename=~".+"}'
>
> for: 1w
>
> The problem is that I get alerted even if the CPU is 1 so I cannot reduce
> it further. I want the alert to fire only number of CPUs > 1.
>
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