AWS CloudFormation (Resource Attributes)

CreationPolicy 

• Wait on resource configuration actions before stack creation proceeds
• Supported by
  • AWS::AutoScaling::AutoScalingGroup
  • AWS::EC2::Instance
  • AWS::CloudFormation::WaitCondition
• Prevents resource reaching CREATE_COMPLETE until signals are received
  
  • Example
    • create instance
    • wait on application configuration
    • signal when code is deployed and service started
• Signal resource
  • cfn-signal helper script
  • SignalResource API
• Properties
  • Count - how many success signals must be received
    • If failure signal received -> rollback
  • Timeout - how long to wait
    • Starts when resource is creating
    • Max 12h, Default 5 minutes
    • ISO duration format (e.g. PT#H#M#S)

UpdatePolicy (AutoScalingGroup)

• How CF handles updates to instances in AutoScaling Groups when CF stack is updated
• Policies
  • AutoScalingReplacingUpdate
    • Used when
      • Launch Configuration change
      • VPCZoneIdentifier (Subnet) change
    • Properties
      • WillReplace - should the group be retained (in-place) or a brand new one created (Blue/Green)
  • AutoScalingRollingUpdate  
    • Used when
      • Launch Configuration change
      • VPCZoneIdentifier (Subnet) change
    • Properties
      • MaxBatchSize - maximum number of instances terminated at a given time
      • MinInstanceInService - minimum number of instances InService
      • WaitOnResourceSignal
        • should CF wait for "signal" after launching new instance (e.g. "I'm ready!")
      • MinSuccessfulInstancesPercent - percent of instances that must signal success
        • Must enable WaitOnResourceSignal
        • Waits until PauseTime
      • PauseTime
        • how long to wait before another instance launched/terminated
        • gives instance time to bootstrap
        • if WaitOnResourceSignal enabled and PauseTime exceeded the update is considered failed -> Rollback initiated
      • SuspendProcess
        • useful to avoid interference from normal AS operations (e.g. AZRebalance)
  • AutoScalingScheduledAction - change to stack that contains ASG with scheduledAction
    • Used when
      • ASG contains ScheduledAction
    • Properties
      • IgnoreUnmodifiedGroupSizeProperties
        • how to handle changes to Min,Max,Desired
        • prevents interference with Scheduled Action which could be in progress
          • Normally CF would set the values on ASG to those defined in the template

UpdatePolicy (Lambda)

• CodeDeployLambdaAliasUpdate
  • Perform CodeDeploy when the version property changes on Alias resource

DeletionPolicy 

• Allows preserving backing up resource on deletion
  • By default all are deleted
• DeletionPolicy overrides the behavior
  • DELETE - default (see exceptions)
  • RETAIN - keeps the resource
    • Can be added to any resource type
  • SNAPSHOT
    • AWS::EC2::Volume
    • AWS::ElastiCache::CacheCluster
    • AWS::ElastiCache::ReplicationGroup
    • AWS::RDS::DBInstance (default when no DBClusterIdentifier)
    • AWS::RDS::DBCluster (default)
    • AWS::Redshift::Cluste

DependsOn 

• Control order of resource creation (imposes sequence)
• Use cases 
  • Override default parallelism
  • Enforce WaitCondition
• Required for
  • VPC-Gateway attachment (IGW or VGW)
    • When in VPC and have Public IP address
      
      • AutoScalingGroups
      • EC2 instances
      • ELB
      • EIP
      • RDS database
      • VPC routes that include Internet Gateway
  • ECS service and AutoScalingGroup
    • Container instances must be running before ECS service is created
  • IAM Role Policy
    • Some Resources make calls to AWS
      • e.g. CodeDeploy::DeploymentGroup
    • Add dependency on the IAM policy

Metadata

• Associate arbitrary JSON/YAML with resource
• Inside you can use Intrinsic Functions, parameters, pseudo-parameters
• Retrieve with describe-stack-resources