Question

You run a fleet of 40 Compute Engine VMs behind a managed instance group serving a stateless API. You configure a Cloud Monitoring alerting policy on the CPU utilization metric with a threshold of 85% sustained for 5 minutes. During a load test, three individual VMs briefly exceeded 85%, but the aggregated policy never fired even though your team wanted to be notified about any single overloaded instance. Investigating the condition, you find the metric is being combined across all instances. Which change to the alerting condition will ensure you are alerted when any individual VM crosses the threshold?

Accepted Answer

Group the time series by the instance_id (or resource) label and evaluate the condition per series, so each VM is assessed independently against the threshold.

Answer

Lower the aggregation alignment period to 1 minute so short spikes on individual VMs are captured in the aggregate.

Answer

Change the cross-series reducer to sum so the combined CPU across all instances crosses 85% faster.

Answer

Add a metric-absence condition alongside the threshold so missing data points from busy VMs trigger the alert.