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Comment by stevefink | Hacker News Reader

Cpu0 : 0.3%us, 0.0%sy, 0.0%ni, 0.0%id, 99.7%wa, 0.0%hi, 0.0%si, 0.0%st <-- EBS subsystem is completely unreachable. I/O wait times are tanked across the board for me (I'm in US-EAST-1).

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What zone? I really wish Amazon would provide that info, instead of saying that it only affects one zone.

Both my MySQL master (I'm not using RDS) and Redis Master servers are affected and are located in zone us-east-1a.

Why do you have two masters in the same AZ?

AFAIK zones are randomized. 1a for me is 1d for you.

That's really interesting if it's true. I had never heard this before. Thanks for the tip.

Do you know why this is?

Supposedly it's for load-balancing purposes. (Most people spin up their machines in 1a.)

Humans are predictable - it wouldn't spread the load across zones very well.

probably to prevent folks from all stacking up in a single AZ.

Just think if someone posted a blog post saying "I've noticed that EBS performance is far better in 1d vs. 1a"

Well, they also return errors if a zone is out of capacity. That seems like it would guard against the issue a bit. But maybe they just don't want to have to field loads of questions about that.

Yeah, for me, 1d experiences the lowest load of all zones. According to the pricing history for spot instances, 1d experiences the fewest price spikes compared to 1a and 1b. I'd be interested to see if other users have noticed the same thing for their zones.

I find that random(5) is the best performing. For okay but consistent performance, random(5) is decent, but you should definitely avoid random(5) due to high load.

I believe it's also a security measure.

It was done due to badly written tools and scripts firing up instances in Availability Zone A every time.

Ahh. Now that you mention it, I think I recall reading that before. It struck me as weird though because 1a was obviously the first one and 1e was recently added. So, would they rebalance my labels in that case?

Unfortunately, there is no meaningful way for them to say which zone because zone labels are different for each user.

It is affecting me on US-EAST-1B

I have instances in two different zones - both are down, although I don't know if AWS's randomization means that my 1a and 1d are actually located in the same logical zone.

The zones map differently per account, but if you've launched instances in different zones for your same account you are for sure in different AZ's.

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