AWS::AutoScaling::WarmPool
The AWS::AutoScaling::WarmPool
resource creates a pool of pre-initialized EC2
instances that sits alongside the Auto Scaling group. Whenever your application needs to scale
out, the Auto Scaling group can draw on the warm pool to meet its new desired capacity.
When you create a warm pool, you can define a minimum size. When your Auto Scaling group scales out and the size of the warm pool shrinks, Amazon EC2 Auto Scaling launches new instances into the warm pool to maintain its minimum size.
For more information, see Warm pools for Amazon EC2 Auto Scaling in the Amazon EC2 Auto Scaling User Guide.
Note
CloudFormation supports the UpdatePolicy
attribute for Auto Scaling groups.
During an update, if UpdatePolicy
is set to
AutoScalingRollingUpdate
, CloudFormation replaces InService
instances only. Instances in the warm pool are not replaced. The difference in which
instances are replaced can potentially result in different instance configurations after the
stack update completes. If UpdatePolicy
is set to
AutoScalingReplacingUpdate
, you do not encounter this issue because
CloudFormation replaces both the Auto Scaling group and the warm
pool.
Syntax
To declare this entity in your AWS CloudFormation template, use the following syntax:
JSON
{ "Type" : "AWS::AutoScaling::WarmPool", "Properties" : { "AutoScalingGroupName" :
String
, "InstanceReusePolicy" :InstanceReusePolicy
, "MaxGroupPreparedCapacity" :Integer
, "MinSize" :Integer
, "PoolState" :String
} }
YAML
Type: AWS::AutoScaling::WarmPool Properties: AutoScalingGroupName:
String
InstanceReusePolicy:InstanceReusePolicy
MaxGroupPreparedCapacity:Integer
MinSize:Integer
PoolState:String
Properties
AutoScalingGroupName
-
The name of the Auto Scaling group.
Required: Yes
Type: String
Update requires: Replacement
InstanceReusePolicy
-
Indicates whether instances in the Auto Scaling group can be returned to the warm pool on scale in. The default is to terminate instances in the Auto Scaling group when the group scales in.
Required: No
Type: InstanceReusePolicy
Update requires: No interruption
MaxGroupPreparedCapacity
-
Specifies the maximum number of instances that are allowed to be in the warm pool or in any state except
Terminated
for the Auto Scaling group. This is an optional property. Specify it only if you do not want the warm pool size to be determined by the difference between the group's maximum capacity and its desired capacity.Important
If a value for
MaxGroupPreparedCapacity
is not specified, Amazon EC2 Auto Scaling launches and maintains the difference between the group's maximum capacity and its desired capacity. If you specify a value forMaxGroupPreparedCapacity
, Amazon EC2 Auto Scaling uses the difference between theMaxGroupPreparedCapacity
and the desired capacity instead.The size of the warm pool is dynamic. Only when
MaxGroupPreparedCapacity
andMinSize
are set to the same value does the warm pool have an absolute size.If the desired capacity of the Auto Scaling group is higher than the
MaxGroupPreparedCapacity
, the capacity of the warm pool is 0, unless you specify a value forMinSize
. To remove a value that you previously set, include the property but specify -1 for the value.Required: No
Type: Integer
Minimum:
-1
Update requires: No interruption
MinSize
-
Specifies the minimum number of instances to maintain in the warm pool. This helps you to ensure that there is always a certain number of warmed instances available to handle traffic spikes. Defaults to 0 if not specified.
Required: No
Type: Integer
Minimum:
0
Update requires: No interruption
PoolState
-
Sets the instance state to transition to after the lifecycle actions are complete. Default is
Stopped
.Required: No
Type: String
Allowed values:
Stopped | Running | Hibernated
Update requires: No interruption
Remarks
CloudFormation won't mark the warm pool as successful (by setting its status to
CREATE_COMPLETE) if there are lifecycle hooks that haven't been completed. If the state of
an instance is Warmed:Pending:Wait
, the lifeycle hook is not considered
complete. For more information, see Use lifecycle hooks with
a warm pool in the Amazon EC2 Auto Scaling User Guide.
If you want to hibernate instances on scale in and there are existing instances in the Auto Scaling group, they must meet the requirements for instance hibernation. If they don't, when instances return to the warm pool, they will fallback to being stopped instead of being hibernated.
Examples
The following example defines a warm pool for an Auto Scaling group.
For more examples, see our GitHub
repository
Auto Scaling group with warm pool
The following template snippet shows an AWS::AutoScaling::WarmPool
resource for an Auto Scaling group where you specify values for the MinSize
and PoolState
properties.
JSON
{ "Resources":{ "myWarmPool":{ "Type":"AWS::AutoScaling::WarmPool", "Properties":{ "AutoScalingGroupName":{ "Ref":"myASG" }, "MinSize":30, "PoolState":"Stopped" } } } }
YAML
--- Resources: myWarmPool: Type: AWS::AutoScaling::WarmPool Properties: AutoScalingGroupName: !Ref myASG MinSize: '30' PoolState: Stopped
See also
-
PutWarmPool in the Amazon EC2 Auto Scaling API Reference