Your ecommerce application connecting to your Cloud SQL for SQL Server is expected to have...

Use a Cloud Function to pull CPU and memory metrics from your Cloud SQL instance and to call a custom service to send alerts.

Use Error Reporting to monitor CPU and memory metrics and to configure SMS notification channels.

Use Cloud Logging to set up a log sink for CPU and memory metrics and to configure a sink destination to send a message to Pub/Sub.

Use Cloud Monitoring to set up an alerting policy for CPU and memory metrics and to configure SMS notification channels.