Auto Scaling Group (ASG)

What it is: A group of EC2 instances managed together for scaling and health management.

What it’s for:

• Maintain desired instance count.
• Replace unhealthy instances automatically.
• Scale out/in based on policies.

Key ideas:

• Settings:
  • Desired capacity
  • Minimum and Maximum
• Works best across multiple AZs for high availability.

Exam cues:

• “replace failed instance automatically” → ASG.
• “keep 2 instances running at all times” → ASG desired=2.

Hard words:

• *desired* /dɪˈzaɪərd/: mong muốn
• *unhealthy* /ʌnˈhelθi/: không khỏe (failing checks)