You see “us-east-1a” on your screen? Surprise: your coworker’s “us-east-1a” isn’t the same place. That mismatch has caused latency spikes, surprise data transfer, and flimsy HA builds for years.
Now there’s a clean fix. EC2 supports Availability Zone IDs (AZ IDs) across its APIs. Stop relying on account-specific AZ names. Target the same physical zone with IDs like “use1-az1.”
If you run multi-account, multi-region, or DR-heavy stacks, this is big. You can co-locate with certainty, simplify migrations, and make “same-zone” actually same. Less guesswork. More reliability. Fewer 2 a.m. incidents.
Here’s why this matters in real life. Shared services like NAT gateways, queues, and caches sit in one account. Apps live in another. If “same AZ” labels don’t align, traffic silently hairpins across zones. That adds milliseconds (annoying for p99s) and shows up as cross-AZ transfer on your bill. AZ IDs stop that drift and put everything exactly where you intend—no detective work.
AZ names are per-account labels. Your “us-west-2a” could be my “us-west-2c.” That’s fine if you live in a single account. It breaks fast at org scale. You think two services are in the “same AZ,” but they’re different physical zones. Cue latency and cross-AZ data transfer.
“Because AZ names are mapped to underlying AZs differently for each account, you can use AZ IDs (for example, use1-az1) to uniquely and consistently identify an AZ across accounts.” — AWS documentation
AZ IDs are static, region-scoped identifiers like “use1-az1.” They represent the actual physical zone and stay consistent across accounts. If you launch with the same AZ ID in two accounts, you land in the same place. That’s the key to reliable co-location in multi-account designs.
First, map AZ names to AZ IDs in each Region you care about. With the AWS CLI:
You’ll see ZoneName (e.g., us-east-1a) and ZoneId (e.g., use1-az1). Store this mapping if you must reference names for legacy pieces, but prefer IDs.
Subnets anchor resources to a specific zone. Create subnets with an AZ ID, and everything launched inherits the right location. Do this across accounts for consistent results. It’s your foundation for deterministic placement.
Tip: many EC2 APIs and IaC tools now support AZ IDs. Subnet creation takes Availability Zone IDs. Prefer the AZ ID option where possible.
This creates a single source of truth and kills ambiguous deployments. You keep flexibility without surprise shifts.
If you run latency-sensitive microservices, brokers, or shared caches, same-zone matters. AZ IDs guarantee you’re pointing to the same physical zone across accounts. No accidental cross-zone hops.
When moving from a legacy account to a new landing zone, you want like-for-like. With AZ IDs, mirror subnets and instances in precise zones. Testing becomes apples-to-apples. Cutovers go smoother.
You design for AZ independence in a Region and Region failover for disasters. AZ IDs help you:
Paired with quotas, reservations, and warm failover, AZ IDs reduce surprises. They matter most when you need them most.
A Region is a separate geographic area (e.g., us-east-1 in Northern Virginia). Each Region has multiple isolated Availability Zones. Regions help with residency, compliance, and latency needs. Services are priced and deployed per Region. That affects budget and strategy.
Most Regions have three or more AZs, though some have two. The exact count varies by Region and changes over time. The only reliable source is the official AWS list. Use it to plan spread.
Bookmark this for the canonical “aws regions and availability zones list”: AWS Global Infrastructure: Regions and Availability Zones
You’ll get the “aws regions list,” each Region’s “aws availability zones list,” and new expansions. Pair that with AZ ID discovery to build stable, portable architectures.
No. You can’t edit an instance’s AZ in place. To “move” it, create an AMI or snapshot, then launch a new instance in the target AZ. Update IPs or target groups, then retire the old one.
Pro tip: if you use Elastic IPs or ENIs, plan the handoff. Some identifiers are AZ-scoped. Test this in non-prod first.
No. AZ names are account-specific labels. Your “us-east-1a” might be my “us-east-1c.” That’s why AZ IDs (e.g., use1-az1) exist—to consistently identify the same physical zone.
Use the EC2 API or CLI to call DescribeAvailabilityZones in a Region. You’ll get ZoneName and ZoneId for each AZ. Record and use the ZoneId for deterministic placement across accounts.
Bonus: store the mapping in Parameter Store, Secrets Manager, or a tiny config service.
Coverage varies by service and API. EC2 and networking constructs support AZ IDs. Some APIs still expect AZ names. When launching compute, placing storage, or creating subnets, prefer flows that take AZ IDs.
A safe default: if a service doesn’t accept AZ IDs, place it inside a subnet that does.
Check the AWS Global Infrastructure page. It’s the source of truth for the aws regions list and each Region’s aws availability zones list. Numbers change as AWS expands, so don’t hard-code them.
It varies by Region and time. Many Regions offer three or more AZs, some have two. Confirm current counts on the Global Infrastructure page, then plan your spread.
Both. Misaligned AZs create cross-AZ data transfer, which is billable in many cases. Aligning with AZ IDs often reduces that hidden tax. Plus, fewer 2 a.m. incidents saves real money.
Close gaps by scripting this flow so “change availability zone of EC2 instance” becomes a safe redeploy.
Strong move: adopt AZ IDs at the edges—subnets, templates, and policies. Then every launch lands exactly where you intend. That’s how you kill the “same name, different place” chaos for good.
“Infrastructure gets easier when your coordinates stop changing.” The punchline is simple: AZ IDs turn fuzzy labels into precise locations. Use them by default, especially across accounts. If you build VPCs, subnets, and templates around AZ IDs, you get predictable performance, smoother migrations, and DR that behaves.
Next step: audit your Regions, discover AZ IDs, lock them into IaC, and standardize subnet creation with AZ IDs. Flip this switch early, and you’ll dodge a pile of future surprises.