Understanding and Mapping Logical to Physical Availability Zones in AWS

Everpure Cloud Dedicated for AWS

Audience

Public

Technology Integrations

Amazon Web Services (AWS)

Source Type

Documentation

When deploying solutions in Amazon Web Services (AWS), understanding the difference between logical and physical Availability Zones (AZs) is critical.

Overview

When deploying AWS-based solutions, understanding the difference between logical and physical Availability Zones (AZs) is critical. Logical AZs are identifiers that Amazon Web Services exposes within a subscription, such as us-east-1a, us-east-1b, or us-east-1c. However, these logical zones are not consistent across subscriptions. This means that us-east-1a in one subscription may map to a different physical datacenter compared to us-east-1a in another subscription. Further information about this subject can be found on Amazon's website.

This discrepancy can create challenges when deploying services such as Everpure Cloud Dedicated solutions across multiple subscriptions. If logical AZs do not align with the same underlying physical datacenter, performance, high availability and disaster recovery strategies may be impacted. This is particularly important when integrating Everpure Cloud products with Elastic VMware Service as placing the two instances in two separate physical datacenters will lead to sub-optimal performance due to additional unnecessary networking hops.

How to Determine Logical vs Physical Availability Zone Mappings

AWS provides a method to query physical zone mappings per subscription using the AWS CLI. This allows customers to verify which logical zone corresponds to which physical datacenter.
1. AWS CLI Command Example:
```
aws ec2 describe-availability-zones \
  --region us-east-1 \
  --query "AvailabilityZones[*].[ZoneName, ZoneId, State]" \
  --output table
```
```
Sample Output:
```
```
  ----------------------------
| AvailabilityZones        |
+-----------+---------+-----+
| us-east-1a| use1-az2| available |
| us-east-1b| use1-az1| available |
| us-east-1c| use1-az3| available |
...
```
  - Zone Name = Logical name in your account.
  - ZoneID = Physical zone ID, consistent across all AWS accounts.
2. Repeat the above command for each unique AWS subscription to determine the physical AZ for each.
Ensure that all integrated components across multiple subscriptions are deployed into the same Physical Availability Zone. This potentially will mean deploying into different logical AZs for each subscription depending on the results from the above commands.

Amazon Web Service's logical vs physical Availability Zone distinction is crucial for customers operating across multiple subscriptions. Without validating mappings, deployments may be unintentionally spread across separate datacenters, impacting performance and resilience. Using the AWS CLI, customers can map logical to physical AZs and ensure deployments are correctly aligned.