What it is: One or more data centers with independent power, cooling, and networking—inside a Region.

What it’s for:

• Build high availability by spreading workloads across multiple AZs.
• Reduce blast radius (a problem in one AZ should not take down everything).

Key ideas:

• A Region has multiple AZs.
• “Multi-AZ” usually means “across at least 2 AZs”.
• AZs are connected with high-bandwidth, low-latency links.

Common exam cues:

• “must survive an AZ outage” → design for Multi-AZ.
• “single AZ deployment risk” → add another AZ.

Hard words:

• *availability* /əˌveɪləˈbɪləti/: tính sẵn sàng
• *outage* /ˈaʊtɪdʒ/: sự cố mất dịch vụ
• *blast radius* /blæst ˈreɪdiəs/: phạm vi ảnh hưởng
• *bandwidth* /ˈbændwɪdθ/: băng thông