Finding the Region for an AWS Resource ID

use concurrent AWS command line requests to search the world for your instance, image, volume, snapshot, …


Amazon EC2 and many other AWS services are divided up into various regions across the world. Each region is a separate geographic area and is completely independent of other regions.

Though this is a great architecture for preventing global meltdown, it can occasionally make life more difficult for customers, as we must interact with each region separately.

One example of this is when we have the id for an AMI, instance, or other EC2 resource and want to do something with it but don’t know which region it is in.

This happens on ServerFault when a poster presents a problem with an instance, provides the initial AMI id, but forgets to specify the EC2 region. In order to find and examine the AMI, you need to look in each region to discover where it is.


You’ll hear a repeating theme when discussing performance in AWS:

To save time, run API requests concurrently.

This principle applies perfectly when performing requests across regions.

Parallelizing requests may seem like it would require an advanced programming language, but since I love using command line programs for simple interactive AWS tasks, I’ll present an easy mechanism for concurrent processing that works in bash.


The following sample code finds an AMI using concurrent aws-cli commands to hit all regions in parallel.

id=ami-25b01138 # example AMI id
type=image # or "instance" or "volume" or "snapshot" or ...

regions=$(aws ec2 describe-regions --output text --query 'Regions[*].RegionName')
for region in $regions; do
     aws ec2 describe-${type}s --region $region --$type-ids $id &>/dev/null && 
         echo "$id is in $region"
    ) &
done 2>/dev/null; wait 2>/dev/null

This results in the following output:

ami-25b01138 is in sa-east-1

By running the queries concurrently against all of the regions, we cut the run time by almost 90% and get our result in a second or two.

Drop this into a script, add code to automatically detect the type of the id, and you’ve got a useful command line tool… which you’re probably going to want to immediately rewrite in Python so there’s not quite so much forking going on.