What it is: A mechanism that tests targets (instances/containers) to see if they are healthy.

What it’s for:

• Route traffic only to healthy targets.
• Improve availability automatically.

Key ideas:

• Health checks can be HTTP (status codes) or TCP connection checks.
• Unhealthy targets are removed from routing until healthy again.

Exam cues:

• “stop sending traffic to failing instance” → health checks + ELB/ASG.

Hard words:

• *mechanism* /ˈmekəˌnɪzəm/: cơ chế
• *status code* /ˈsteɪtəs koʊd/: mã trạng thái (HTTP 200/404…)
• *removed* /rɪˈmuːvd/: bị loại khỏi