Finding Amazon Linux AMI IDs for Cloudformation Mappings

So … this post came about because I use Cloudformation for all my infrastructure in AWS.

When you create an EC2 instance, you need a base AMI, and for all my tests I usually just use the Amazon Linux AMI.

Now, the issue here is that an AMI is region-bound, so the Amazon Linux AMI that Amazon provides has different IDs in each AWS region.. so usually I would use a Mappings configuration in Cloudformation to specify the right Amazon Linux AMI ID according to the region I’m playing in.

Now, the name of the AMI is the same in all region! Thanks AWS for consistency!
Plus, the AMI name is unique per region!

So let me tell you my evolution on finding the AMIs for each region.

1. Find a cloudformation template that uses Cloudformation Mappings for Amazon Linux AMI

That’s years ago! Don’t judge me :D

So here, I would first go on Google, and try to find a Cloudformation sample that uses Cloudformation Mappings, then copy / paste the Mappings section.

Pros
uhh… None?

Cons
Well, first of all, very manual.. right.

Also, Amazon delivers new AMI with new updates all the time, but the Cloudformation stack might not have the latest AMI referenced.

I have never thought I would need again so I didn’t bother bookmarking the link … guess what..
I’ve always needed it..

2. Find the AMI IDs from the console

See how I finally decided to use an AWS tool rather than Google to find the information? Winner!!

I would go in the AWS console, find the AMI I want, and filter in the AMI console on the name then change each region and filtering on the same AMI name.. and copy / paste was my best friend. Ever.

Pros

  • I could see if there was a new Amazon Linux AMI.

Cons

  • Long, painful … my life sucks kind of way.

3. Using AND the console AND the awscli

Then I decided.. let’s automate this to some level, so I wrote a script that would loop through each region and get the image id based on the AMI name.
Here I would first go in the Console, same as before, and get the AMI name.

Disclaimer: For arguments sake, I didn’t include all the regions here, but there’s an easier way later anyway!

After that, I would run the following script:

for region in ap-southeast-2 us-east-1 us-west-2
do
  echo -n "${region}: "
  aws ec2 describe-images --filters Name=name,Values=<ami_name> --query "Images[0].ImageId" --region $region
done

–query might sound obscure to you..
Well, this is a jmespath query, which you can read more about here.

4. Step into the future. AWSCLI only solution!

Now now… I’m better than this hey!
Well, awscli has a way to list all the regions.. and I finally decided that I had enough with my lazyness, and automate the whole shizzel:

for region in $(aws ec2 describe-regions --query "Regions[].RegionName" --output text)
do
  echo "${region}: $(aws ec2 describe-images --owners amazon --filters Name=name,Values=amzn-ami-hvm-*s3 --query "reverse(sort_by(Images, &CreationDate))[0].ImageId" --output text --region $region)"
done

This snippet loops through all the regions, and return all the Instance-store based Amazon Linux AMI, and sorting in a descending fashion on the CreationDate.

JmesPath only sorts lexicographically.. it’s not aware of dates.
But this works because the field CreationDate that AWS returns is in ISO 8601 format, which is lexicographical.

Of course, you can format the output the way you want, and feel free to modify the filter to match the AMI you want.

There you go! Hopefully, that helps, Use it, Love it, Live it!