This is specific to Amazon Web Services: if I understand correctly, this essentially consists on passing the bulk of the data not directly form a server in one Availability Zone (data center?) to another, but to store it in S3 and pass only messages about it (metadata) which are tiny in comparison.
Apparently, transmission between any AZ and S3 is flat rate while AZ<->AZ is metered which is where the savings come from.
Not only AWS, but GCP also charges for network communication across availability zones. Moreover, your understanding is correct.The key here is the use of S3 as a shared storage feature. Reading and writing S3-like object storage across AZs will not incur cross-AZ traffic fees. Cloud vendors charge for API call fees and storage fees for object storage.
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This is specific to Amazon Web Services: if I understand correctly, this essentially consists on passing the bulk of the data not directly form a server in one Availability Zone (data center?) to another, but to store it in S3 and pass only messages about it (metadata) which are tiny in comparison.
Apparently, transmission between any AZ and S3 is flat rate while AZ<->AZ is metered which is where the savings come from.
Not only AWS, but GCP also charges for network communication across availability zones. Moreover, your understanding is correct.The key here is the use of S3 as a shared storage feature. Reading and writing S3-like object storage across AZs will not incur cross-AZ traffic fees. Cloud vendors charge for API call fees and storage fees for object storage.