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QuestionQ201

Ensuring solution and operations excellence

You configured an autoscaling instance group to handle web traffic for an upcoming launch. After setting the instance group as a backend service for an HTTP(S) load balancer, you observe that virtual machine (VM) instances are terminated and relaunched every minute. The instances have no public IP addresses.

You verified with the curl command that every instance returns the appropriate web response. You want to make sure that the backend is configured properly.

What should you do?

  • A Ensure that a firewall rules exists to allow source traffic on HTTP/HTTPS to reach the load balancer.
  • B Assign a public IP to each instance and configure a firewall rule to allow the load balancer to reach the instance public IP.
  • C Ensure that a firewall rule exists to allow load balancer health checks to reach the instances in the instance group.
  • D Create a tag on each instance with the name of the load balancer. Configure a firewall rule with the name of the load balancer as the source and the instance tag as the destination.
Explanation

Google Cloud load-balancer backends require an ingress firewall rule that allows health-check probes to reach the backend VMs on the health-check protocol and port. If the probes are blocked, the default implied ingress-deny rule causes the backends to be considered unhealthy, which can trigger replacement of instances in a managed instance group. Public IP addresses are not required for backend VMs.

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