====== Auto Scaling ======

**What it is:** Automatically adjusts capacity (number of instances) based on demand.

**What it’s for:**
  * Handle traffic spikes and reduce cost during low usage.
  * Improve availability by replacing unhealthy instances.

**Key ideas:**
  * Uses [[aws:compute:auto-scaling:asg|Auto Scaling Group (ASG)]]
  * Scaling decisions based on metrics (CPU, requests, custom metrics).

**Exam cues:**
  * “traffic varies, need automatic scaling” → Auto Scaling + ASG.

**Hard words:**
  * *capacity* /kəˈpæsəti/: năng lực/tài nguyên
  * *demand* /dɪˈmænd/: nhu cầu
  * *metric* /ˈmetrɪk/: chỉ số đo

**Child pages:**
  * [[.:auto-scaling:scheduled-scaling|Scheduled Scaling (Auto Scaling)]]
  * [[.:auto-scaling:az-rebalance|AZ Rebalance (Auto Scaling)]]
  * [[.:auto-scaling:health-checks:elb-alb|ASG + ALB Health Checks (ELB health checks)]] 
  * [[.:auto-scaling:replace-unhealthy|Replace Unhealthy Instance (ASG)]]