GCP provides health checks to check response from VM instance. This tutorial describes how to create and use health checks for load balancers.
gcloud compute health-checks create tcp test-health-chk \
--port 80
Created [https://www.googleapis.com/compute/v1/projects/*******/global/healthChecks/test-health-chk].
NAME PROTOCOL
test-health-chk TCP
Category: GCP