====== 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)