Which configuration follows Google-recommended best practices for accessing a web application on Compute Engine via SSH?

Configuring Cloud Identity-Aware Proxy (IAP) API for SSH access with private IP addresses is aligned with Google-recommended best practices because it enhances the security of your web application running on Compute Engine. By using IAP, you can establish secure connections to your VM instances without exposing them to the internet directly through public IP addresses. This method ensures that only authenticated users can access the application, and it leverages Google's secure infrastructure for identity and access management.

Implementing IAP also simplifies the management of SSH access, as you don't need to manage firewall rules or external IP addresses separately for each instance. Instead, access is mediated through IAP, which enforces security policies and provides logging capabilities. This makes the overall architecture more secure and easier to manage, aligning with best practices for cloud security and access management.

In contrast, other configurations may expose the application to security vulnerabilities or may not follow the principle of least privilege. For instance, allowing all ingress traffic to the instances could lead to unauthorized access and potential breaches. Utilizing unique external IP addresses for each server also increases management complexity and does not enhance security in the same way that using IAP does. Thus, setting up IAP for SSH access with private IP addresses represents a best practices approach for