Access CloudFormation using an interface endpoint (AWS PrivateLink)

You can use AWS PrivateLink to create a private connection between your VPC and CloudFormation. You can access CloudFormation as if it were in your VPC, without the use of an internet gateway, NAT device, VPN connection, or AWS Direct Connect connection. Instances in your VPC don't need public IP addresses to access CloudFormation.

You establish this private connection by creating an interface endpoint, powered by AWS PrivateLink. We create an endpoint network interface in each subnet that you enable for the interface endpoint. These are requester-managed network interfaces that serve as the entry point for traffic destined for CloudFormation.

CloudFormation supports making calls to all of its API actions through the interface endpoint.

Considerations for CloudFormation VPC endpoints

Before you set up an interface endpoint, first make sure you have met the prerequisites in the Access an AWS service using an interface VPC endpoint topic in the AWS PrivateLink Guide.

The following additional prerequisites and considerations apply when setting up an interface endpoint for CloudFormation:

• If you have resources within your VPC that must respond to a custom resource request or a wait condition, make sure that they have access to the required CloudFormation-specific Amazon S3 buckets. CloudFormation has S3 buckets in each Region to monitor responses to a custom resource request or a wait condition. If a template includes custom resources or wait conditions in a VPC, the VPC endpoint policy must allow users to send responses to the following buckets:

  • For custom resources, permit traffic to the cloudformation-custom-resource-response-region bucket. When using custom resources, AWS Region names don't contain dashes. For example, uswest2.

  • For wait conditions, permit traffic to the cloudformation-waitcondition-region bucket. When using wait conditions, AWS Region names do contain dashes. For example, us-west-2.

  If the endpoint policy blocks traffic to these buckets, CloudFormation won't receive responses and the stack operation fails. For example, if you have a resource in a VPC in the us-west-2 Region that must respond to a wait condition, the resource must be able to send a response to the cloudformation-waitcondition-us-west-2 bucket.

  For a list of AWS Regions where CloudFormation is currently available, see the AWS CloudFormation endpoints and quotas page in the Amazon Web Services General Reference.

• VPC endpoints currently don't support cross-Region requests — ensure that you create your endpoint in the same Region in which you plan to issue your API calls to CloudFormation.

• VPC endpoints only support Amazon-provided DNS through Route 53. If you want to use your own DNS, you can use conditional DNS forwarding. For more information, see DHCP options sets in Amazon VPC in the Amazon VPC User Guide.

• The security group attached to the VPC endpoint must allow incoming connections on port 443 from the private subnet of the VPC.

Creating an interface VPC endpoint for CloudFormation

You can create a VPC endpoint for CloudFormation using either the Amazon VPC console or the AWS Command Line Interface (AWS CLI). For more information, see Create a VPC endpoint in the AWS PrivateLink Guide.

Create an interface endpoint for CloudFormation using the following service name:

• com.amazonaws.region.cloudformation

If you enable private DNS for the interface endpoint, you can make API requests to CloudFormation using its default Regional DNS name. For example, cloudformation.us-east-1.amazonaws.com.

Creating a VPC endpoint policy for CloudFormation

An endpoint policy is an IAM resource that you can attach to an interface endpoint. The default endpoint policy allows full access to CloudFormation through the interface endpoint. To control the access allowed to CloudFormation from your VPC, attach a custom endpoint policy to the interface endpoint.

An endpoint policy specifies the following information:

• The principals that can perform actions (AWS accounts, IAM users, and IAM roles).

• The actions that can be performed.

• The resources on which the actions can be performed.

For more information, see Control access to VPC endpoints using endpoint policies in the AWS PrivateLink Guide.

Example: VPC endpoint policy for CloudFormation actions

The following is an example of an endpoint policy for CloudFormation. When attached to an endpoint, this policy grants access to the listed CloudFormation actions for all principals on all resources. The following example denies all users the permission to create stacks through the VPC endpoint, and allows full access to all other actions on the CloudFormation service.

{
  "Statement": [
    {
      "Action": "cloudformation:*", 
      "Effect": "Allow", 
      "Principal": "*", 
      "Resource": "*"
    },
    {
      "Action": "cloudformation:CreateStack", 
      "Effect": "Deny", 
      "Principal": "*", 
      "Resource": "*"
    }
  ]
}