Functions

You can use functions in your configuration files to populate values for resource properties with information from other resources or from Elastic Beanstalk configuration option settings. Elastic Beanstalk supports AWS CloudFormation functions (Ref, Fn::GetAtt, Fn::Join), and one Elastic Beanstalk-specific function, Fn::GetOptionSetting.

Ref

Use Ref to retrieve the default string representation of an AWS resource. The value returned by Ref depends on the resource type, and sometimes depends on other factors as well. For example, a security group (AWS::EC2::SecurityGroup) returns either the name or ID of the security group, depending on if the security group is in a default Amazon Virtual Private Cloud (Amazon VPC), EC2 classic, or a custom VPC.

{ "Ref" : "resource name" }

Note

For details on each resource type, including the return value(s) of Ref, see AWS Resource Types Reference in the AWS CloudFormation User Guide.

From the sample Auto Scaling lifecycle hook:

Resources:
  lifecyclehook:
    Type: AWS::AutoScaling::LifecycleHook
    Properties:
      AutoScalingGroupName: { "Ref" : "AWSEBAutoScalingGroup" }

You can also use Ref to retrieve the value of a AWS CloudFormation parameter defined elsewhere in the same file or in a different configuration file.

Fn::GetAtt

Use Fn::GetAtt to retrieve the value of an attribute on an AWS resource.

{ "Fn::GetAtt" : [ "resource name", "attribute name"] }

From the sample Auto Scaling lifecycle hook:

Resources:
  lifecyclehook:
    Type: AWS::AutoScaling::LifecycleHook
    Properties:
      RoleARN: { "Fn::GetAtt" : [ "hookrole", "Arn"] }

See Fn::GetAtt for more information.

Fn::Join

Use Fn::Join to combine strings with a delimiter. The strings can be hard-coded or use the output from Fn::GetAtt or Ref.

{ "Fn::Join" : [ "delimiter", [ "string1", "string2" ] ] }

See Fn::Join for more information.

Fn::GetOptionSetting

Use Fn::GetOptionSetting to retrieve the value of a configuration option setting applied to the environment.

"Fn::GetOptionSetting":
  Namespace: "namespace"
  OptionName: "option name"
  DefaultValue: "default value"

From the storing private keys example:

Resources:
  AWSEBAutoScalingGroup:
    Metadata:
      AWS::CloudFormation::Authentication:
        S3Auth:
          type: "s3"
          buckets: ["elasticbeanstalk-us-west-2-123456789012"]
          roleName: 
            "Fn::GetOptionSetting": 
              Namespace: "aws:autoscaling:launchconfiguration"
              OptionName: "IamInstanceProfile"
              DefaultValue: "aws-elasticbeanstalk-ec2-role"