CreationPolicy attribute - AWS CloudFormation
AppStream 2.0 creation policyAmazon EC2 Auto Scaling creation propertiesExamples

CreationPolicy attribute

Associate the CreationPolicy attribute with a resource to prevent its status from reaching create complete until AWS CloudFormation receives a specified number of success signals or the timeout period is exceeded. To signal a resource, you can use the cfn-signal helper script or SignalResource API. CloudFormation publishes valid signals to the stack events so that you track the number of signals sent.

The creation policy is invoked only when CloudFormation creates the associated resource. Currently, the only CloudFormation resources that support creation policies are:

Use the CreationPolicy attribute when you want to wait on resource configuration actions before stack creation proceeds. For example, if you install and configure software applications on an EC2 instance, you might want those applications to be running before proceeding. In such cases, you can add a CreationPolicy attribute to the instance, and then send a success signal to the instance after the applications are installed and configured. For a detailed Amazon EC2 example, see Deploy applications on Amazon EC2.

AppStream 2.0 creation policy

Amazon AppStream configuration for a creation policy.

Syntax

JSON

{
    "CreationPolicy": {
        "StartFleet": {
            "Type": "Boolean"
        }
    }
}

YAML

CreationPolicy:
  StartFleet:
    Type: Boolean
StartFleet

Starts the specified fleet.

Required: No

Amazon EC2 Auto Scaling creation properties

Amazon EC2 Auto Scaling configuration for a creation policy.

Syntax

JSON

"CreationPolicy" : {
  "AutoScalingCreationPolicy" : {
    "MinSuccessfulInstancesPercent" : Integer
  },
  "ResourceSignal" : {    
    "Count" : Integer,
    "Timeout" : String
  }
}

YAML

CreationPolicy:
  AutoScalingCreationPolicy:
    MinSuccessfulInstancesPercent: Integer
  ResourceSignal:    
    Count: Integer
    Timeout: String

Amazon EC2 Auto Scaling creation properties

Amazon EC2 Auto Scaling configuration for a creation policy.

AutoScalingCreationPolicy

For a new Amazon EC2 Auto Scaling group, specifies the number of instances that must signal success before setting the group's status to CREATE_COMPLETE.

MinSuccessfulInstancesPercent

Specifies the percentage of instances in an Amazon EC2 Auto Scaling that must signal success before setting the group's status to CREATE_COMPLETE. You can specify a value from 0 to 100. CloudFormation rounds to the nearest tenth of a percent. For example, if you create five instances with a minimum successful percentage of 50, three instances must signal success. If an instance doesn't send a signal within the time specified by the Timeout property, CloudFormation assumes that the instance wasn't created.

Default: 100

Type: Integer

Required: No

ResourceSignal

When CloudFormation creates the associated resource, configures the number of required success signals and the length of time that CloudFormation waits for those signals.

Count

The number of success signals CloudFormation must receive before it sets the resource status as CREATE_COMPLETE. If the resource receives a failure signal or doesn't receive the specified number of signals before the timeout period expires, the resource creation fails and CloudFormation rolls the stack back.

Default: 1

Type: Integer

Required: No

Timeout

The length of time that CloudFormation waits for the number of signals that was specified in the Count property. The timeout period starts after CloudFormation stabilizes the resource, and the timeout expires no sooner than the time you specify but can occur shortly thereafter. The maximum time that you can specify is 12 hours.

The value must be in ISO8601 duration format, in the form: PT#H#M#S, where each # is the number of hours, minutes, and seconds, respectively. For best results, specify a period of time that gives your instances plenty of time to get up and running. A shorter timeout can cause a rollback.

Default: PT5M (5 minutes)

Type: String

Required: No

Examples

Auto Scaling group

The following example shows how to add a creation policy to an Amazon EC2 Auto Scaling group. The creation policy requires three success signals and times out after 15 minutes. Use the cfn-signal helper script to signal when an instance creation process has completed successfully.

To have instances wait for an Elastic Load Balancing health check before they signal success, add a health-check verification by using the cfn-init helper script. For an example, see the verify_instance_health command in the sample templates for Amazon EC2 Auto Scaling rolling updates in our GitHub repository.

JSON

"AutoScalingGroup": {
  "Type": "AWS::AutoScaling::AutoScalingGroup",
  "Properties": {
    "VPCZoneIdentifier":[ "subnetIdAz1", "subnetIdAz2", "subnetIdAz3" ],
    "LaunchTemplate":{
      "LaunchTemplateId":{
        "Ref":"logicalName"
      },
      "Version":{
        "Fn::GetAtt":[
          "logicalName",
          "LatestVersionNumber"
        ]
      }
    },
    "MinSize": "1",
    "MaxSize": "4"
  },
  "CreationPolicy": {
    "ResourceSignal": {
      "Count": "3",
      "Timeout": "PT15M"
    }
  }
}

YAML

AutoScalingGroup:
  Type: AWS::AutoScaling::AutoScalingGroup
  Properties:
    VPCZoneIdentifier:
      - subnetIdAz1
      - subnetIdAz2
      - subnetIdAz3
    LaunchTemplate:
      LaunchTemplateId: !Ref logicalName
      Version: !GetAtt logicalName.LatestVersionNumber
    MinSize: '1'
    MaxSize: '4'
  CreationPolicy:
    ResourceSignal:
      Count: '3'
      Timeout: PT15M

WaitCondition

The following example shows how to add a creation policy to a wait condition for CloudFormation resources beyond Amazon EC2.

To signal the WaitCondition resource, use the SignalResource API. This API is designed to work with WaitCondition resources that you configure using a CreationPolicy.

JSON

"WaitCondition" : {
    "Type" : "AWS::CloudFormation::WaitCondition",
    "CreationPolicy" : {
        "ResourceSignal" : {
            "Timeout" : "PT15M",
            "Count" : "5"
        }
    }
}

YAML

WaitCondition:
  Type: AWS::CloudFormation::WaitCondition
  CreationPolicy:
    ResourceSignal:
      Timeout: PT15M
      Count: 5