Two instances in the Dublin region went down together around 2:40 PM. Both reported failed network-reachability health checks, but there was no corresponding incident on the service health dashboard. They were in the same availability zone, so I wondered whether an underlying host, rack, or network issue could have caused both failures. Restarting the instances resolved the problem, so this is mostly a curiosity: has anyone seen a similar localized failure, and would this type of event normally appear on the health status page?
2 Answers
A rack-level failure is a plausible explanation. If the two instances happened to be placed together, a problem affecting that rack or nearby host infrastructure could take them down without affecting the entire availability zone. Smaller infrastructure incidents do not always generate a public health event.
Since the instances were in the same availability zone, check their placement and host relationship if you have access to that information. They may have shared a physical host or nearby infrastructure, which would explain why they failed at the same time. A physical host failure is another reasonable possibility.
That was my thinking too. A short note on the health dashboard would still be useful, even just to confirm the issue was on the provider side rather than something we did.