3 ms·

Most AZs are 1 DC, but some are too large to fit in a single building. I don't think there is a distance limit between AZs but instead a latency limit. James

by dgemm 6y ago

Most AZs are 1 DC, but some are too large to fit in a single building. 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

SideburnsOfDoom 6y ago
> I don't think there is a distance limit between AZs but instead a latency limit 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-latency-between-aws-availability-zones 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/95-1/ 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.
- bbgm 6y ago
  You need to take into account the speed of light in fiber optics and switching latency. For fiber you're looking at about 5 µs/km
  - SideburnsOfDoom 6y ago
    > about 5 µs/km 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.
darkwater 6y ago
> EBS sticking in the same AZ has nothing to do with distance and everything to do with keeping failures within an AZ But they could be synced and if one AZ goes down another is elected as the primary copy. Most storage solutions handle that.

by dgemm 6y ago

SideburnsOfDoom 6y ago

> I don't think there is a distance limit between AZs but instead a latency limit 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-latency-between-aws-availability-zones 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/95-1/ 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.

bbgm 6y ago
You need to take into account the speed of light in fiber optics and switching latency. For fiber you're looking at about 5 µs/km
- SideburnsOfDoom 6y ago
  > about 5 µs/km 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.

darkwater 6y ago

> EBS sticking in the same AZ has nothing to do with distance and everything to do with keeping failures within an AZ But they could be synced and if one AZ goes down another is elected as the primary copy. Most storage solutions handle that.