Define and reference variables in the AWSTOE application - EC2 Image Builder

Define and reference variables in the AWSTOE application

Variables provide a way to label data with meaningful names that can be used throughout a program. You can define custom variables with simple and readable formats for complex workflows, and reference them in an AWSTOE document.

This section provides information to help you define constants that can be referenced from an AWSTOE application document, including syntax, name constraints, and examples.


Constants are immutable variables that cannot be modified or overridden once defined. Constants can be defined using values in the constants section of an AWSTOE document.

Constant name constraints

  • Minimum length: 3 characters.

  • Maximum length: 128 characters.

  • Must contain at least one English letter (a-z, A-Z).

  • Cannot contain special characters, with the exception of "-" or "_".

  • Must be a unique name within the document.


constants: - <name>: type: <constant type> value: <constant value>
Key name Required Description



Name of the constant. Must be unique name in document (including names of parameters).


Yes Value of the constant.


Yes Type of the constant. Supported type is string.


Referencing constants in step inputs

name: Download AWS CLI version 2 schemaVersion: 1.0 constants: - Source: type: string value: phases: - name: build steps: - name: Download action: WebDownload inputs: - source: '{{ Source }}' destination: 'C:\Windows\Temp\AWSCLIV2.msi'

Referencing constants in loop inputs

name: PingHosts schemaVersion: 1.0 constants: - Hosts: type: string value:, phases: - name: build steps: - name: Ping action: ExecuteBash loop: forEach: list: '{{ Hosts }}' delimiter: ',' inputs: commands: - ping -c 4 {{ loop.value }}