How to get the VCPU count of an instance in Google Cloud Platform

Question

I'm trying to fetch timeseries points of VCPU count for a VM instance using monitoring_v3 API. While reading the documentation, I encountered two metric types

instance/cpu/guest_visible_vcpus
instance/cpu/reserved_cores

Which metric type is appropriate for VCPU count and why?

Answer 1

Google documents those metrics here.

Which one to use depends on what you are trying to measure and the types of instances you are running. In most cases, the reserved_cores represents real CPU power. guest_visible_vcpu represents what the guest appears to have, which might appear to be a lot more than the reserved amount.

instance/cpu/guest_visible_vcpu

Number of vCPUs visible inside the guest. For many GCE machine types, the number of vCPUs visible inside the guest is equal to the compute.googleapis.com/instance/cpu/reserved_cores metric. For shared-core machine types, the number of guest-visible vCPUs differs from the number of resereved cores. For example, e2-small instances have two vCPUs visible inside the guest and 0.5 fractional vCPUs reserved. Therefore, for an e2-small instance, compute.googleapis.com/instance/cpu/guest_visible_vcpus has a value of 2 and compute.googleapis.com/instance/cpu/reserved_cores has a value of 0.5. Sampled every 60 seconds. After sampling, data is not visible for up to 240 seconds.

instance/cpu/reserved_cores

Number of vCPUs reserved on the host of the instance. Sampled every 60 seconds. After sampling, data is not visible for up to 240 seconds.