Regions, Availability Zones and Edge Locations

Lantern’s maintainers live in Lisbon and most of its users are in Portugal. When they create their first resource, the AWS console asks a question they have never had to answer: which Region? The old server sat in one data centre somewhere and nobody thought about it. On AWS, where your things run is a design decision, and it affects latency, law, resilience and your bill.

Regions: where your data lives

A Region is a separate geographic area with its own copy of most AWS services. Each has a code you will type often: eu-west-1 is Ireland, eu-central-1 is Frankfurt, eu-south-2 is Spain, us-east-1 is North Virginia. Regions are isolated from each other. A bucket you create in eu-west-1 stores its data there, and AWS does not copy it to another Region unless you configure replication.

You can list the Regions your account can use from the terminal (you install the CLI in lesson four):

aws ec2 describe-regions --query "Regions[].RegionName" --output text

Not every service or feature launches in every Region at the same time, and prices differ between Regions. Some newer Regions are opt-in, so they do not appear until you enable them.

How to choose

Use this order, and stop at the first rule that decides it:

1. Data rules. If a law or a contract says personal data stays in the EU, every non-EU Region is out.
2. Latency to users. Closer is faster. For Lantern, the Iberian and western European Regions are the candidates.
3. Service availability. Check that every service you plan to use exists in that Region.
4. Price. The same instance can cost noticeably more in one Region than another.

Lantern ends up in a European Region close to Portugal. The exact choice matters less than making it on purpose and then using it consistently.

Availability Zones: surviving a bad day

Inside each Region are Availability Zones. An AZ is one or more discrete data centres with redundant power, networking and cooling, physically separated from the other AZs in the Region, yet linked to them by fast, low-latency private fibre. Most Regions have three or more.

The point of AZs is independent failure. A flood, fire or power cut in one AZ should not touch the others. So the rule for anything important is: run it in at least two AZs.

AZs have two kinds of label. The name, such as eu-west-1a, is what you pick in the console. The AZ ID, such as euw1-az1, always means the same physical zone in every account. In some older Regions, accounts created before November 2025 have names mapped independently, so your eu-west-1a may be another team’s eu-west-1b. When you coordinate with another account, compare AZ IDs:

aws ec2 describe-availability-zones --region eu-west-1 \
  --query "AvailabilityZones[].{Name:ZoneName,Id:ZoneId}" --output table

This tells you which services are tied to what. Global services, such as IAM and CloudFront, are configured once for the whole account. Regional services, such as S3 buckets, Lambda functions and DynamoDB tables, live in one Region and AWS spreads them across AZs for you. Zonal resources, such as an EC2 instance or an EBS volume, live in exactly one AZ, and multi-AZ resilience is your job.

Edge locations: closer than any Region

Regions are few. Edge locations are many: smaller sites in hundreds of cities that run Amazon CloudFront (the content delivery network) and Amazon Route 53 (DNS). When a visitor in Porto loads a Lantern poster, CloudFront can serve a cached copy from a nearby edge location instead of fetching it from the bucket every time. That is how Lantern will survive its next viral evening in section four.

What geography costs

Data transfer is metered differently depending on where it goes. Traffic coming into AWS from the internet is generally free. Traffic between AZs in the same Region is charged per gigabyte, traffic between Regions costs more, and data sent out to the internet is charged too, which CloudFront can reduce through caching. You don’t need numbers to design well, only this habit: every arrow in your diagram that crosses an AZ or Region line has a price. Multi-AZ is worth paying for when downtime hurts; a cross-Region copy of everything usually isn’t, for a site Lantern’s size.

Next you will see where AWS’s job ends and yours begins, and secure the account itself.