There hasn't been an acknowledged S3 outage since April 2009 that we can find. Also, we use two different buckets in different geographic availability zones to allow us to stay up if one AZ goes out. Finally, our biggest projects are cached in CloudFront, which would serve a stale cached item if the backend were unavailable.

Do you 'invalidate' all files when pushing an update or do you use a low cache expiry value for CloudFront?

In particular, I am thinking of edge cases where a news story has a typo/other important correction and you want to update just that story. What is your strategy? How is it impacted by caching done by CloudFront? Thanks.

Thanks for the clarification, all! I learned some shizzle.

Yes and yes. Yes, it is possible for S3 to go down and yes uptime is very high. For their purposes, S3 uptime is much higher than they can reasonably sustain with in house hosting.

Plus if you combine S3 with CloudFront you have a very potent combination for uptime