Template formats - AWS CloudFormation

Template formats

You can author CloudFormation templates in JSON or YAML formats. The same CloudFormation features and functions are available for both formats.

JSON

The following example shows the structure of a JSON-formatted template with all available sections.

{ "AWSTemplateFormatVersion" : "version date", "Description" : "JSON string", "Metadata" : { template metadata }, "Parameters" : { set of parameters }, "Rules" : { set of rules }, "Mappings" : { set of mappings }, "Conditions" : { set of conditions }, "Transform" : { set of transforms }, "Resources" : { set of resources }, "Outputs" : { set of outputs } }

YAML

The following example shows the structure of a YAML-formatted template with all available sections.

--- AWSTemplateFormatVersion: "version date" Description: String Metadata: template metadata Parameters: set of parameters Rules: set of rules Mappings: set of mappings Conditions: set of conditions Transform: set of transforms Resources: set of resources Outputs: set of outputs

When deciding which format to use, pick the format that you're most comfortable working in. Also consider that YAML inherently provides some features, such as commenting, that aren't available in JSON.

The following example shows a YAML template with inline comments.

AWSTemplateFormatVersion: "2010-09-09" Description: A sample template Resources: MyEC2Instance: #An inline comment Type: "AWS::EC2::Instance" Properties: ImageId: "ami-0ff8a91507f77f867" #Another comment -- This is a Linux AMI InstanceType: t2.micro KeyName: testkey BlockDeviceMappings: - DeviceName: /dev/sdm Ebs: VolumeType: io1 Iops: 200 DeleteOnTermination: false VolumeSize: 20

Specifications

CloudFormation supports the following JSON and YAML specifications:

JSON

CloudFormation follows the ECMA-404 JSON standard. For more information about the JSON format, see http://www.json.org.

YAML

CloudFormation supports the YAML Version 1.1 specification with a few exceptions. CloudFormation doesn't support the following features:

  • The binary, omap, pairs, set, and timestamp tags

  • Aliases

  • Hash merges

For more information about YAML, see https://yaml.org/.

Learn more

For each resource you specify in your template, you define its properties and values using the specific syntax rules of either JSON or YAML. For more information about the template syntax for each format, see Template sections.