UpdatePolicy Attribute

Use the UpdatePolicy attribute to specify how AWS CloudFormation handles updates to the AWS::AutoScaling::AutoScalingGroup, AWS::Lambda::Alias, or AWS::ElastiCache::ReplicationGroup resources.

AutoScalingReplacingUpdate Policy

To specify how AWS CloudFormation handles replacement updates for an Auto Scaling group, use the AutoScalingReplacingUpdate policy. This policy enables you to specify whether AWS CloudFormation replaces an Auto Scaling group with a new one or replaces only the instances in the Auto Scaling group.

Syntax

"UpdatePolicy" : {
  "AutoScalingReplacingUpdate" : {
    "WillReplace" : Boolean
  }
}

UpdatePolicy:
  AutoScalingReplacingUpdate:
    WillReplace: Boolean

Properties

AutoScalingRollingUpdate Policy

To specify how AWS CloudFormation handles rolling updates for an Auto Scaling group, use the AutoScalingRollingUpdate policy. Rolling updates enable you to specify whether AWS CloudFormation updates instances that are in an Auto Scaling group in batches or all at once.

Be aware that, during stack update rollback operations, CloudFormation uses the UpdatePolicy configuration specified in the template before the current stack update operation. For example, suppose you have updated the MaxBatchSize in your stack template's UpdatePolicy from 1 to 10. You then perform a stack update, and that update fails and CloudFormation initiates an update rollback operation. In such a case, CloudFormation will use 1 as the maximum batch size, rather than 10. For this reason, we recommend you make changes to the UpdatePolicy configuration in a stack update separate from, and prior to, any updates to the AWS::AutoScaling::AutoScalingGroup resource that are likely to trigger rolling updates.

Syntax

"UpdatePolicy" : {
  "AutoScalingRollingUpdate" : {
    "MaxBatchSize" : Integer,
    "MinInstancesInService" : Integer,
    "MinSuccessfulInstancesPercent" : Integer
    "PauseTime" : String,
    "SuspendProcesses" : [ List of processes ],
    "WaitOnResourceSignals" : Boolean
  }
}

UpdatePolicy:
  AutoScalingRollingUpdate:
    MaxBatchSize: Integer
    MinInstancesInService: Integer
    MinSuccessfulInstancesPercent: Integer
    PauseTime: String
    SuspendProcesses:
      - List of processes
    WaitOnResourceSignals: Boolean

Properties

AutoScalingScheduledAction Policy

To specify how AWS CloudFormation handles updates for the MinSize, MaxSize, and DesiredCapacity properties when the AWS::AutoScaling::AutoScalingGroup resource has an associated scheduled action, use the AutoScalingScheduledAction policy.

With scheduled actions, the group size properties of an Auto Scaling group can change at any time. When you update a stack with an Auto Scaling group and scheduled action, AWS CloudFormation always sets the group size property values of your Auto Scaling group to the values that are defined in the AWS::AutoScaling::AutoScalingGroup resource of your template, even if a scheduled action is in effect.

If you do not want AWS CloudFormation to change any of the group size property values when you have a scheduled action in effect, use the AutoScalingScheduledAction update policy to prevent AWS CloudFormation from changing the MinSize, MaxSize, or DesiredCapacity properties unless you have modified these values in your template.

Syntax

"UpdatePolicy" : {
  "AutoScalingScheduledAction" : {
    "IgnoreUnmodifiedGroupSizeProperties" : Boolean
  }
}

UpdatePolicy:
  AutoScalingScheduledAction:
    IgnoreUnmodifiedGroupSizeProperties: Boolean

Properties

CodeDeployLambdaAliasUpdate Policy

To perform an AWS CodeDeploy deployment when the version changes on an AWS::Lambda::Alias resource, use the CodeDeployLambdaAliasUpdate update policy.

Syntax

"UpdatePolicy" : {
  "CodeDeployLambdaAliasUpdate" : {
    "AfterAllowTrafficHook" : String,
    "ApplicationName" : String,
    "BeforeAllowTrafficHook" : String,
    "DeploymentGroupName" : String
  }
}

UpdatePolicy:
  CodeDeployLambdaAliasUpdate:
    AfterAllowTrafficHook: String
    ApplicationName: String
    BeforeAllowTrafficHook: String
    DeploymentGroupName: String

Properties

For an example that specifies the UpdatePolicy attribute for an AWS::Lambda::Alias resource, see Lambda Alias Update Policy.

UseOnlineResharding Policy

To modify a replication group's shards by adding or removing shards, rather than replacing the entire AWS::ElastiCache::ReplicationGroup resource, use the UseOnlineResharding update policy.

If UseOnlineResharding is set to true, you can update the NumNodeGroups and NodeGroupConfiguration properties of the AWS::ElastiCache::ReplicationGroup resource, and CloudFormation will update those properties without interruption. When UseOnlineResharding is set to false, or not specified, updating the NumNodeGroups and NodeGroupConfiguration properties results in CloudFormation replacing the entire AWS::ElastiCache::ReplicationGroup resource.

The UseOnlineResharding update policy has no properties.

Things to consider when setting the UseOnlineResharding update policy to true:

For more information on modifying replication groups, see ModifyReplicationGroupShardConfiguration.html in the Amazon ElastiCache API Reference.

Syntax

"UpdatePolicy" : {
  "UseOnlineResharding" : Boolean
}

UpdatePolicy:
  UseOnlineResharding: Boolean

Examples

The following examples show how to add an update policy to an Auto Scaling group and how to maintain availability when updating metadata.

Add an UpdatePolicy to an Auto Scaling Group

The following example shows how to add an update policy. During an update, the Auto Scaling group updates instances in batches of two and keeps a minimum of one instance in service. Because the WaitOnResourceSignals flag is set, the Auto Scaling group waits for new instances that are added to the group. The new instances must signal the Auto Scaling group before it updates the next batch of instances.

"ASG" : {
   "Type" : "AWS::AutoScaling::AutoScalingGroup",
   "Properties" : {
      "AvailabilityZones" : [
         "us-east-1a",
         "us-east-1b"
      ],
      "DesiredCapacity" : "1",
      "LaunchConfigurationName" : {
         "Ref" : "LaunchConfig"
      },
      "MaxSize" : "4",
      "MinSize" : "1"
   },
   "UpdatePolicy" : {
      "AutoScalingScheduledAction" : {
         "IgnoreUnmodifiedGroupSizeProperties" : "true"
      },
      "AutoScalingRollingUpdate" : {
         "MinInstancesInService" : "1",
         "MaxBatchSize" : "2",
         "WaitOnResourceSignals" : "true",
         "PauseTime" : "PT10M"
      }
   }
 },
"ScheduledAction" : {
   "Type" : "AWS::AutoScaling::ScheduledAction",
   "Properties" : {
      "AutoScalingGroupName" : {
         "Ref" : "ASG"
      },
      "DesiredCapacity" : "2",
      "StartTime" : "2017-06-02T20 : 00 : 00Z"
   }
}

ASG:
  Type: 'AWS::AutoScaling::AutoScalingGroup'
  Properties:
    AvailabilityZones:
    - us-east-1a
    - us-east-1b
    DesiredCapacity: '1'
    LaunchConfigurationName:
      Ref: LaunchConfig
    MaxSize: '4'
    MinSize: '1'
  UpdatePolicy:
    AutoScalingScheduledAction:
      IgnoreUnmodifiedGroupSizeProperties: 'true'
    AutoScalingRollingUpdate:
      MinInstancesInService: '1'
      MaxBatchSize: '2'
      WaitOnResourceSignals: 'true'
      PauseTime: PT10M
ScheduledAction:
  Type: 'AWS::AutoScaling::ScheduledAction'
  Properties:
    AutoScalingGroupName:
      Ref: ASG
    DesiredCapacity: '2'
    StartTime: '2017-06-02T20 : 00 : 00Z'

AutoScalingReplacingUpdate Policy

The following example declares a policy that forces an associated Auto Scaling group to be replaced during an update. For the update to succeed, a percentage of instances (specified by the MinSuccessfulPercentParameter parameter) must signal success within the Timeout period.

"UpdatePolicy" : {
  "AutoScalingReplacingUpdate" : {
    "WillReplace" : "true"
  }
},
"CreationPolicy" : {
  "ResourceSignal" : {
    "Count" : { "Ref" : "ResourceSignalsOnCreate"},
    "Timeout" : "PT10M"
  },
  "AutoScalingCreationPolicy" : {
    "MinSuccessfulInstancesPercent" : { "Ref" : "MinSuccessfulPercentParameter" }
  }
}

UpdatePolicy:
  AutoScalingReplacingUpdate:
    WillReplace: 'true'
CreationPolicy:
  ResourceSignal:
    Count: !Ref 'ResourceSignalsOnCreate'
    Timeout: PT10M
  AutoScalingCreationPolicy:
    MinSuccessfulInstancesPercent: !Ref 'MinSuccessfulPercentParameter'

Maintain Availability When Updating the Metadata for the cfn-init Helper Script

When you install software applications on your instances, you might use the AWS::CloudFormation::Init metadata key and the cfn-init helper script to bootstrap the instances in your Auto Scaling group. AWS CloudFormation installs the packages, runs the commands, and performs other bootstrapping actions described in the metadata.

When you update only the metadata (for example, when updating a package to another version), you can use the cfn-hup helper daemon to detect and apply the updates. However, the cfn-hup daemon runs independently on each instance. If the daemon happens to runs at the same time on all instances, your application or service might be unavailable during the update. To guarantee availability, you can force a rolling update so that AWS CloudFormation updates your instances one batch at a time.

To force a rolling update, change the logical ID of the launch configuration resource, and then update the stack and any references pointing to the original logic ID (such as the associated Auto Scaling group). AWS CloudFormation triggers a rolling update on the Auto Scaling group, replacing all instances.

Original Template

"LaunchConfig": {
  "Type" : "AWS::AutoScaling::LaunchConfiguration",
  "Metadata" : {
    "Comment" : "Install a simple PHP application",
    "AWS::CloudFormation::Init" : {
    ...
    }
  }
}

Updated Logical ID

"LaunchConfigUpdateRubygemsPkg": {
  "Type" : "AWS::AutoScaling::LaunchConfiguration",
  "Metadata" : {
    "Comment" : "Install a simple PHP application",
    "AWS::CloudFormation::Init" : {
    ...
    }
  }
}

Lambda Alias Update Policy

The following example specifies the UpdatePolicy attribute for an AWS::Lambda::Alias resource. All the details for the deployment are defined by the application and deployment group that are passed into the policy.

"Alias": {
  "Type": "AWS::Lambda::Alias",
  "Properties": {
    "FunctionName": {
      "Ref": "LambdaFunction"
    },
    "FunctionVersion": {
      "Fn::GetAtt": [
        "FunctionVersionTwo",
        "Version"
      ]
    },
    "Name": "MyAlias"
  },
  "UpdatePolicy": {
    "CodeDeployLambdaAliasUpdate": {
      "ApplicationName": {
        "Ref": "CodeDeployApplication"
      },
      "DeploymentGroupName": {
        "Ref": "CodeDeployDeploymentGroup"
      },
      "BeforeAllowTrafficHook": {
        "Ref": "PreHookLambdaFunction"
      },
      "AfterAllowTrafficHook": {
        "Ref": "PreHookLambdaFunction"
      }
    }
  }
}

Alias:
  Type: 'AWS::Lambda::Alias'
  Properties:
    FunctionName: !Ref LambdaFunction
    FunctionVersion: !GetAtt FunctionVersionTwo.Version
    Name: MyAlias
  UpdatePolicy:
    CodeDeployLambdaAliasUpdate:
      ApplicationName: !Ref CodeDeployApplication
      DeploymentGroupName: !Ref CodeDeployDeploymentGroup
      BeforeAllowTrafficHook: !Ref PreHookLambdaFunction
      AfterAllowTrafficHook: !Ref PreHookLambdaFunction

On this page:

• AutoScalingReplacingUpdate Policy
• AutoScalingRollingUpdate Policy
• AutoScalingScheduledAction Policy
• CodeDeployLambdaAliasUpdate Policy
• UseOnlineResharding Policy
• Examples