====== Fault Isolation ======

**What it is:** Designing so that a failure in one component (or one AZ) does not break the whole system.

**What it’s for:**
  * Reduce impact and recover faster.
  * Improve reliability without overbuilding everything.

**How to apply:**
  * Spread across multiple AZs.
  * Use separate subnets per AZ.
  * Use load balancers and health checks.
  * Avoid single points of failure.

**Exam cues:**
  * “prevent a single failure from taking down the app” → fault isolation (often Multi-AZ + redundancy).

**Hard words:**
  * *isolation* /ˌaɪsəˈleɪʃn/: cô lập
  * *redundancy* /rɪˈdʌndənsi/: dự phòng
  * *single point of failure* /ˌsɪŋɡl pɔɪnt əv ˈfeɪljər/: điểm lỗi duy nhất