How do you ensure that compute instances in a load balancer can be reached from the internet?

The correct choice focuses on the necessity of configuring firewall rules to allow HTTP traffic. In Google Cloud, simply having compute instances reachable from the internet involves ensuring that the network security settings permit incoming connections on the desired ports, commonly port 80 for HTTP and port 443 for HTTPS.

Setting up the appropriate firewall rules is crucial because Google Cloud's default firewall configuration may block external traffic for security reasons. By explicitly allowing HTTP (and potentially HTTPS) traffic, you ensure that users on the internet can reach the compute instances through the load balancer. This configuration is essential for directing web traffic correctly and maintaining application accessibility.

While adding a public IP to each instance can technically allow direct access, it is not a best practice in load balancer scenarios, as it complicates the network architecture and not all applications require individual public IPs for every instance. Deploying instances within a public subnet alone does not guarantee they are reachable since firewall rules can still restrict access. Similarly, using an external load balancer for internal health checks addresses load balancing functionality rather than ensuring general accessibility from the internet.