Query for the latest Amazon Linux AMI IDs using AWS Systems Manager Parameter Store

This post is courtesy of Arend Castelein, Software Development Engineer – AWS

Want a simpler way to query for the latest Amazon Linux AMI? AWS Systems Manager Parameter Store already allows for querying the latest Windows AMI. Now, support has been expanded to include the latest Amazon Linux AMI. Each Amazon Linux AMI now has its own Parameter Store namespace that is public and describable. Upon querying, an AMI namespace returns only its regional ImageID value.

The namespace is made up of two parts:

• Parameter Store Prefix (tree): /aws/service/ami-amazon-linux-latest/
• AMI name alias: (example) amzn-ami-hvm-x86_64-gp2

You can determine an Amazon Linux AMI alias by taking the full AMI name property of an Amazon Linux public AMI and removing the date-based version identifier. A list of these AMI name properties can be seen by running one for the following Amazon EC2 queries.

Using the AWS CLI:

aws ec2 describe-images --owners amazon --filters "Name=name,Values=amzn*" --query 'sort_by(Images, &CreationDate)[].Name'

Using PowerShell:

Get-EC2ImageByName -Name amzn* | Sort-Object CreationDate | Select-Object Name

For example, amzn2-ami-hvm-2017.12.0.20171208-x86_64-gp2 without the date-based version becomes amzn2-ami-hvm-x86_64-gp2.

When you add the public Parameter Store prefix namespace to the AMI alias, you have the Parameter Store name of “/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2”.

Each unique AMI namespace always remains the same. You no longer need to pattern match on name filters, and you no longer need to sort through CreationDate AMI properties. As Amazon Linux AMIs are patched and new versions are released to the public, AWS updates the Parameter Store value with the latest ImageID value for each AMI namespace in all supported Regions.

Before this release, finding the latest regional ImageID for an Amazon Linux AMI involved a three-step process. First, using an API call to search the list of available public AMIs. Second, filtering the results by a given partial string name. Third, sorting the matches by CreationDate property and selecting the newest ImageID. Querying AWS Systems Manager greatly simplifies this process.

Querying for the latest AMI using public parameters

After you have your target namespace, your query can be created to retrieve the latest Amazon Linux AMI ImageID value. Each Region has an exact replica namespace containing its Region-specific ImageID value.

Using the AWS CLI:

aws ssm get-parameters --names /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2 --region us-east-1 

Using PowerShell:

Get-SSMParameter -Name /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2 -region us-east-1

Always launch new instances with the latest ImageID

After you have created the query, you can embed the command as a command substitution into your new instance launches.

Using the AWS CLI:

aws ec2 run-instances --image-id $(aws ssm get-parameters --names /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2 --query 'Parameters[0].[Value]' --output text) --count 1 --instance-type m4.large

Using PowerShell:

New-EC2Instance -ImageId ((Get-SSMParameterValue -Name /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2).Parameters[0].Value) -InstanceType m4.large -AssociatePublicIp $true

This new instance launch always results in the latest publicly available Amazon Linux AMI for amzn2-ami-hvm-x86_64-gp2. Similar embedding can be used in a number of automation process, docs, and coding languages.

Display a complete list of all available Public Parameter Amazon Linux AMIs

You can also query for the complete list of AWS Amazon Linux Parameter Store namespaces available.

Using the AWS CLI:

aws ssm get-parameters-by-path --path "/aws/service/ami-amazon-linux-latest" --region us-east-1

Using PowerShell:

Get-SSMParametersByPath -Path "/aws/service/ami-amazon-linux-latest" -region us-east-1

Here’s an example list retrieved from a get-parameters-by-path call:

/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-ebs
/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2
/aws/service/ami-amazon-linux-latest/amzn2-ami-minimal-hvm-x86_64-ebs
/aws/service/ami-amazon-linux-latest/amzn-ami-hvm-x86_64-ebs
/aws/service/ami-amazon-linux-latest/amzn-ami-hvm-x86_64-gp2
/aws/service/ami-amazon-linux-latest/amzn-ami-hvm-x86_64-s3
/aws/service/ami-amazon-linux-latest/amzn-ami-minimal-hvm-x86_64-ebs
/aws/service/ami-amazon-linux-latest/amzn-ami-minimal-hvm-x86_64-s3

Launching latest Amazon Linux AMI in an AWS CloudFormation stack

AWS CloudFormation also supports Parameter Store. For more information, see Integrating AWS CloudFormation with AWS Systems Manager Parameter Store. Here’s an example of how you would reference the latest Amazon Linux AMI in a CloudFormation template.

# Use public Systems Manager Parameter
Parameters:
  LatestAmiId:
    Type: 'AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>'
    Default: '/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2'

Resources:
 Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: !Ref LatestAmiId