Regions, Availability Zones and Edge Locations

Inkwell's two web servers run in AWS. One night, a power fault hits a single AWS data centre. Does the shop go dark? That depends entirely on where Inkwell placed its servers. AWS's physical layout is designed so that one failure need not stop you — but only if you use the layout well.

The rule

Pick a Region for your users; spread across zones for survival.

AWS's global infrastructure has three layers:

• Region: a geographic area such as Mumbai (ap-south-1) or Frankfurt (eu-central-1). AWS runs more than thirty of them. Regions are independent of each other, and your data stays in the Region you choose unless you move it. You pick a Region for latency (close to users), law (some data must stay in a country), price (costs differ slightly) and service availability (new services reach some Regions first).
• Availability Zone (AZ): each Region contains several AZs, usually three or more. An AZ is one or more data centres with separate power, cooling and networking, located kilometres apart from the other zones but linked to them by fast, low-latency private connections. Names look like ap-south-1a, ap-south-1b.
• Edge location: hundreds of smaller sites in cities worldwide. Services such as CloudFront (a content delivery network) and Route 53 (DNS) use them to serve content and answers close to users.

Zones are the key to resilience. A problem in one zone should not affect the others, so an app spread across two or more zones keeps running when one fails.

The shortcut

Read placement as "Region by users, AZs by count": choose the Region nearest your users (checking any legal rules), then count how many distinct zones your copies sit in. One zone, however many copies, means one point of failure.

The trap is thinking two servers automatically means high availability. Two servers in the same zone share that zone's fate; the power fault takes both. Copies only protect you when they sit in different zones.

Drills

Answer fast — trust the rule.

Remember

• Pick a Region for your users; spread across zones for survival.
• Region (area) contains AZs (isolated data centres); edge locations serve content near users.
• Trap: many copies in one zone is still one point of failure.