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Is it possible to obtain information about an instance (attached volumes, information about those volumes, etc.) if an AZ has an outage? Will this require any special configuration, or will the AWS CLI commands still work if the AZ that an instance is in is down? Where is information about an instance stored?

Craig Watson
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user409449
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  • Depends on the nature of the outage. Amazon's outages are rarely "entire AZ dropped off the face of the earth" - they're typically a single-service failure, with knock-on effects at times (i.e. an EBS failure takes out ELBs). The console and APIs may *or may not* work during one. – ceejayoz May 15 '17 at 17:07
  • If an AZ has an outage nothing will work. If an AZ has a partial outage it's anyone's guess what will work. It's best to assume it'll be completely down. Make sure you have things architected for the uptime and reliability you need. Sometimes that's one AZ, sometimes that's multiple AZs, sometimes that's multiple regions. The most recent failure in US-EAST-1 effectively took out the whole region. – Tim May 15 '17 at 19:12

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Instance metadata (e.g. which availability zone the instance is in, its IP address, instance ID, AMI ID) is not stored with the instance.

If an AZ-wide outage happens, the data should remain and will be queryable via the CLI and the AWS Console, but the instance will not be reachable.

The effects of an AZ-wide outage however will mean that the CLI and Console interfaces themselves may be affected - e.g. during a CloudFront outage a few years back, the Console itself was effectively knocked offline as it used CloudFront for image assets.

Craig Watson
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    Do you know how the instance metadata system works? Does it run per region, tolerating a single AZ outage? How about a region outage, which would require it to run globally? I haven't seen anywhere that this information is shared by AWS. – Tim May 16 '17 at 21:02
  • AFAIK it's not necessarily shared of publicised by Amazon, however being on the receiving end of a number of AWS outages, snafus and quirks, I can state with a high degree of certainty that metadata is not stored with instances _in my experience_ - most likely is that it is contained within a region (hence needing to tab-switch across regions within the EC2 console). – Craig Watson May 16 '17 at 21:09
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One of the option is to run periodic queries to keep a copy of these things locally e.g. following command using the AWS Command-Line Interface (CLI) gives you list of all instances in this region along with attached EBS volumeId.

aws ec2 describe-instances --region us-west-2

Following command gives list of all-volumes in a given region

aws ec2 describe-volumes --region us-west-2

If you use any cloud monitoring solution, they would have a copy of these things too (probably detailed volume info might be missing).

John Rotenstein
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dy10
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