[AWS] independently map Availability Zones too names for each account
AWS documentation
This means that eu-west-1a in my account is not necessarily the same as eu-west-1a in your account.
Why does this matter? for example if you want to share subnets across accounts. Or maybe you want to ensure that services in different accounts are not in the same availability zone.
So how can you achieve this? use availability zone ids which are unique and consistent identifiers for availability zones.
See more here – https://docs.aws.amazon.com/ram/latest/userguide/working-with-az-ids.html
Tom Ron 