https://aws.amazon.com/about-aws/global-infrastructure/regio...

> AZ’s are physically separated by a meaningful distance, many kilometers, from any other AZ, although all are within 100 km (60 miles) of each other.

This answers my previous question I guess

EDIT: well, actually, no. I wanted to know distance between DC in the same AZ :)

https://wikileaks.org/amazon-atlas/map/

It was in response to parent comment saying "the datacenter", which seems to be assuming that there was only one. But there will be multiple.

I don't think there is a distance limit between AZs but instead a latency limit. James Hamilton covered it in one of his keynotes a few years ago.

EBS sticking in the same AZ has nothing to do with distance and everything to do with keeping failures within an AZ

Ok, fleshing that out via google:

"The connection between AZs is expected to typically achieve low single-digit millisecond latency between them on average."

https://knowledgebase.progress.com/articles/Article/expected...

and

1 light-millisecond = 299792.458 meters, so nearly 300 km / 186 miles.

https://www.translatorscafe.com/unit-converter/en-US/length/...

So in 2 milliseconds, light travels 599km or 372 miles.

That's a _hard_ limit. IIRC, modern communications is at a fraction of lightspeed, which would lower it.

There's no reason _not_ to have the AZs for a region in the same metro area, so separated by 10s of km, tops.

10km = 0.0333 light-milliseconds.

Which puts it at 200km in a millisecond (5 microseconds is 1 / 200 of a millisecond.) Like I said "modern communications is at a fraction of lightspeed", although I didn't want to guess what fraction. But 200 / 600 = 1/3 is a reasonable fraction, seems legit.

But they could be synced and if one AZ goes down another is elected as the primary copy. Most storage solutions handle that.