February 28, 2017. S3 went down and took down a good portion of AWS and the Internet in general. For almost the entire time that it was down, the AWS status page showed green because the up/down metrics were hosted on... you guessed it... S3.
I used to work at a company where the SLA was measured as the percentage of successful requests on the server. If the load balancer (or DNS or anything else network) was dropping everything on the floor, you'd have no 500s and 100% SLA compliance.
I’ve been customer for at least four separate products where this was true.
I can’t explain why Saucelabs was the most grating one, but it was. I think it’s because they routinely experienced 100% down for 1% of customers, and we were in that one percent about twice a year. <long string of swears omitted>
I spent enough time ~15 years back to find an external monitoring service that did not run on AWS and looked like a sustainable business instead of a VC fueled acquisition target - for our belts-n-braces secondary monitoring tool since it's not smart to trust CloudWatch to be able to send notifications when it's AWS's shit that's down.
Sadly while I still use that tool a couple of jobs/companies later - I no longer recommend it because it migrated to AWS a few years back.
(For now, my out-of-AWS monitoring tool is a bunch of cron jobs running on a collections of various inexpensive vpses and my and other dev's home machines.)
Interestingly, the reason I originally looked for and started using it was an unapproved "shadow IT" response to an in-house Nagios setup that was configured and managed so badly it had _way_ more downtime than any of the services I'd get shouted about at if customers noticed them down before we did...
(No disrespect to Nagios, I'm sure a competently managed installation is capable of being way better than what I had to put up with.)
