Average EC2 Uptime?

Question

Curious as to 99.95% uptime REALLY means; Is it really going to go down 7 minutes a month? Please post your longest/average uptimes on EC2, thanks.

Answer 1

Usually uptime is calculated in a yearly basis. So if you have a Service Level Agreement for 99.95% this means:

365 * 0.0005 = 0.1825 days or 4.38 hours

If during a year of service there is an outage and your system is down for more than that, then you are liable for compensation.

As of your question, I have a server running unstopped in EC2 for about 3 months now. I would say that their uptime is good, but if you have a mission critical application you definitely need to have a fail-over solution. A good uptime only means that they will be able to respond to an outage quickly. Even a 99.9999% uptime won't be able to save you if you aren't prepared for an outage.

Answer 2

Read the SLA carefully (http://aws.amazon.com/ec2-sla/) they only count "Region Unavailable" as downtime, and what is more they only count it as downtime if the region is down for 5 consecutive minutes.

“"Annual Uptime Percentage” is calculated by subtracting from 100% the percentage of 5 minute periods during the Service Year in which Amazon EC2 was in the state of “Region Unavailable.”

By my count this mean any downtime of less then 4 minutes is not countable. Also if they do break the SLA they are only in for %10 of the month in which you had largest downtime bill. So if they where down for all of January and your bill was $100 they would apply a $10 credit to your account.

I would have a hard time convensing my boss that this is a serious product with a SLA like that.