The service monitoring documentation has been moved and renamed to SLO monitoring.
SLO monitoring helps you monitor the health of Google Cloud microservices by providing the tools to set up alerting policies on the performance of service-level objectives (SLOs).
The feature provides automatic support for Cloud Service Mesh, Istio on Google Kubernetes Engine, App Engine, and Cloud Endpoints and supports the creation of custom services for Google Kubernetes Engine (GKE). Use of this feature requires no code changes in your applications.
For more information, see SLO monitoring.