====== Replace Unhealthy Instance (ASG) ======

**What it is:** The process where Auto Scaling removes unhealthy instances and adds replacements to keep desired capacity.

**What it’s for:**
  * Self-healing: keep the fleet healthy automatically.

**Default behavior (exam detail):**
  * ASG creates a scaling activity to **terminate the unhealthy instance first**.
  * Then (while/after termination), another scaling activity **launches a new instance** to replace it. :contentReference[oaicite:6]{index=6}

**Note:**
  * You can change “launch sooner” behavior using an **instance maintenance policy**. :contentReference[oaicite:7]{index=7}

**Hard words:**
  * *terminate* /ˈtɝːmɪneɪt/: chấm dứt (tắt/huỷ instance)
  * *replace* /rɪˈpleɪs/: thay thế
  * *maintenance policy* /ˈmeɪntənəns ˈpɑːləsi/: chính sách bảo trì