Explanation

To automatically recreate unhealthy VMs in a Managed Instance Group (MIG), you must configure autohealing with health checks. Here's why:

Autohealing with Health Checks:

• Autohealing is a feature of MIGs that automatically recreates instances that fail health checks
• You define health checks (HTTP, HTTPS, TCP, or SSL) that monitor the health of your instances
• When an instance fails the health check for a specified period, the MIG automatically recreates it
• This ensures your application remains available and healthy

Why other options are incorrect:

A) Firewall rules:

• Firewall rules control network traffic but don't automatically recreate unhealthy instances
• They can affect connectivity but not instance health management

C) Preemptible instances:

• Preemptible instances are low-cost, short-lived VMs that can be terminated by Google Cloud
• This is about cost optimization, not health monitoring and auto-recovery

D) Cloud Monitoring alerts:

• While Cloud Monitoring can alert you about unhealthy instances, it doesn't automatically recreate them
• You would need to set up additional automation (like Cloud Functions) to respond to alerts

Key Takeaway: Autohealing with health checks is the built-in MIG feature specifically designed to automatically replace unhealthy instances, making it the correct solution for this requirement.