Control CloudFormation access with AWS Identity and Access Management

With AWS Identity and Access Management (IAM), you can create IAM users and control their access to specific resources in your AWS account. When you use IAM, you can control what users can do with CloudFormation, such as whether they can view stack templates, create stacks, or delete stacks.

Beyond CloudFormation-specific actions, you can manage what AWS services and resources are available to each user. That way, you can control which resources users can access when they use CloudFormation. For example, you can specify which users can create Amazon EC2 instances, terminate database instances, or update VPCs. Those same permissions apply anytime they use CloudFormation to do those actions.

Use the information in the following sections to control who can access CloudFormation. We will also explore how to authorize IAM resource creation in templates, give applications running on EC2 instances the permissions they need, and make use of temporary security credentials for enhanced security in your AWS environment.

Defining IAM identity-based policies for CloudFormation

To give access to CloudFormation, you need to create and assign IAM policies that give your IAM identities (such as users or roles) permission to call the API actions they need.

With IAM identity-based policies, you can specify allowed or denied actions and resources, as well as the conditions under which actions are allowed or denied. CloudFormation supports specific actions, resources, and condition keys.

If you're new to IAM, start by familiarizing yourself with the elements of an IAM JSON policy. For more information, see IAM JSON policy element reference in the IAM User Guide. To learn how to create IAM policies, complete the tutorial Create and attach your first customer managed policy in the IAM documentation.

Policy actions for CloudFormation

In the Action element of your IAM policy statement, you can specify any API action that CloudFormation offers. You must prefix the action name with the lowercase string cloudformation:. For example: cloudformation:CreateStack, cloudformation:CreateChangeSet, and cloudformation:UpdateStack.

To specify multiple actions in a single statement, separate them with commas, as follows:

"Action": [ "cloudformation:action1", "cloudformation:action2" ]

You can also specify multiple actions using wildcards. For example, you can specify all actions whose names begin with the word Get, as follows:

"Action": "cloudformation:Get*"

To see a complete list of actions associated with the cloudformation service prefix, see Actions, resources, and condition keys for AWS CloudFormation and Actions, resources, and condition keys for AWS Cloud Control API in the Service Authorization Reference.

Examples

The following shows an example of a permissions policy that grants permissions to view CloudFormation stacks.

{
    "Version":"2012-10-17",
    "Statement":[{
        "Effect":"Allow",
        "Action":[
            "cloudformation:DescribeStacks",
            "cloudformation:DescribeStackEvents",
            "cloudformation:DescribeStackResource",
            "cloudformation:DescribeStackResources"
        ],
        "Resource":"*"
    }]
}

Users who create or delete stacks need additional permissions based on their stack templates. For example, if your template describes an Amazon SQS queue, users must have permissions for both CloudFormation and Amazon SQS actions, as shown in the following sample policy.

{
    "Version":"2012-10-17",
    "Statement":[{
        "Effect":"Allow",
        "Action":[
            "sqs:*",
            "cloudformation:CreateStack",
            "cloudformation:DescribeStacks",
            "cloudformation:DescribeStackEvents",
            "cloudformation:DescribeStackResources",
            "cloudformation:GetTemplate",
            "cloudformation:ValidateTemplate"  
        ],
        "Resource":"*"
    }]
}

Console-specific actions for CloudFormation

Users of the CloudFormation console require additional permissions beyond those needed for the AWS Command Line Interface or CloudFormation APIs. These additional permissions support console-specific features such as template uploads to Amazon S3 buckets and drop-down lists for AWS-specific parameter types.

For all actions listed below, grant permissions to all resources; don't limit them to specific stacks or buckets.

The following action is used only by the CloudFormation console and is not documented in the API reference. The action allows users to upload templates to Amazon S3 buckets.

When users upload templates, users also require the following Amazon S3 permissions:

To see values in the parameter drop-down lists for templates with AWS-specific parameter types, users need permissions to make the corresponding describe API calls. For example, the following permissions are required when these parameter types are used in the template:

For more information about AWS-specific parameter types, see Specify existing resources at runtime with CloudFormation-supplied parameter types.

Policy resources for CloudFormation

In an IAM policy statement, the Resource element specifies the object or objects that the statement covers. For CloudFormation, each IAM policy statement applies to the resources that you specify using their Amazon Resource Names (ARNs). The specific ARN format depends on the resource.

For a complete list of CloudFormation resource types and their ARNs, see Resource types defined by AWS CloudFormation in the Service Authorization Reference. To learn with which actions you can specify with each resource's ARN, see Actions defined by AWS CloudFormation.

You can specify actions for a specific stack, as shown in the following policy example. When you provide an ARN, replace the placeholder text with your resource-specific information.

{
    "Version":"2012-10-17",
    "Statement":[{
        "Effect":"Deny",
        "Action":[
            "cloudformation:DeleteStack",
            "cloudformation:UpdateStack"
        ],
        "Resource":"arn:aws:cloudformation:region:account-id:stack/MyProductionStack/*"
    }]
}

The policy above uses a wild card at the end of the stack name so that delete stack and update stack are denied on both the full stack ID (such as arn:aws:cloudformation:region:account-id:stack/MyProductionStack/abc9dbf0-43c2-11e3-a6e8-50fa526be49c) and the stack name (such as MyProductionStack).

To allow AWS::Serverless transforms to create a change set, include the arn:aws:cloudformation:region:aws:transform/Serverless-2016-10-31 resource-level permission, as shown in the following policy.

 {
    "Version": "2012-10-17",
    "Statement": [{
        "Effect": "Allow",
        "Action": [
            "cloudformation:CreateChangeSet"
        ],
        "Resource": "arn:aws:cloudformation:region:aws:transform/Serverless-2016-10-31"
    }]
}

Policy condition keys for CloudFormation

In an IAM policy statement, you can optionally specify conditions that control when a policy is in effect. For example, you can define a policy that allows users to create a stack only when they specify a certain template URL. You can define CloudFormation-specific conditions and AWS-wide conditions, such as DateLessThan, which specifies when a policy stops taking effect. For more information and a list of AWS-wide conditions, see Condition in IAM policy elements reference in IAM User Guide.

The following list describes the CloudFormation-specific conditions. These conditions are applied only when users create or update stacks:

For examples of IAM policies that use condition keys to control access, see Example IAM identity-based policies for CloudFormation.

Acknowledging IAM resources in CloudFormation templates

Before you can create a stack, CloudFormation validates your template. During validation, CloudFormation checks your template for IAM resources that it might create. IAM resources, such as a user with full access, can access and modify any resource in your AWS account. Therefore, we suggest that you review the permissions associated with each IAM resource before proceeding so that you don't unintentionally create resources with escalated permissions. To ensure that you've done so, you must acknowledge that the template contains those resources, giving CloudFormation the specified capabilities before it creates the stack.

You can acknowledge the capabilities of CloudFormation templates by using the CloudFormation console, AWS Command Line Interface (AWS CLI), or API:

Managing credentials for applications running on Amazon EC2 instances

If you have an application that runs on an Amazon EC2 instance and needs to make requests to AWS resources such as Amazon S3 buckets or an DynamoDB table, the application requires AWS security credentials. However, distributing and embedding long-term security credentials in every instance that you launch is a challenge and a potential security risk. Instead of using long-term credentials, like IAM user credentials, we recommend that you create an IAM role that is associated with an Amazon EC2 instance when the instance is launched. An application can then get temporary security credentials from the Amazon EC2 instance. You don't have to embed long-term credentials on the instance. Also, to make managing credentials easier, you can specify just a single role for multiple Amazon EC2 instances; you don't have to create unique credentials for each instance.

For a template snippet that shows how to launch an instance with a role, see IAM role template examples.

Granting temporary access (federated access)

In some cases, you might want to grant users with no AWS credentials temporary access to your AWS account. Rather than creating and deleting long-term credentials whenever you want to grant temporary access, use AWS Security Token Service (AWS STS). For example, you can use IAM roles. From one IAM role, you can programmatically create and then distribute many temporary security credentials (which include an access key, secret access key, and security token). These credentials have a limited life, so they cannot be used to access your AWS account after they expire. You can also create multiple IAM roles in order to grant individual users different levels of permissions. IAM roles are useful for scenarios like federated identities and single sign-on.

A federated identity is a distinct identity that you can use across multiple systems. For enterprise users with an established on-premises identity system (such as LDAP or Active Directory), you can handle all authentication with your on-premises identity system. After a user has been authenticated, you provide temporary security credentials from the appropriate IAM user or role. For example, you can create an administrators role and a developers role, where administrators have full access to the AWS account and developers have permissions to work only with CloudFormation stacks. After an administrator is authenticated, the administrator is authorized to obtain temporary security credentials from the administrators role. However, for developers, they can obtain temporary security credentials from only the developers role.

You can also grant federated users access to the AWS Management Console. After users authenticate with your on-premises identity system, you can programmatically construct a temporary URL that gives direct access to the AWS Management Console. When users use the temporary URL, they won't need to sign in to AWS because they have already been authenticated (single sign-on). Also, because the URL is constructed from the users' temporary security credentials, the permissions that are available with those credentials determine what permissions users have in the AWS Management Console.

You can use several different AWS STS APIs to generate temporary security credentials. For more information about which API to use, see Compare AWS STS credentials in the IAM User Guide.

CloudFormation interacts with many other AWS services. When you use temporary security credentials with CloudFormation, verify that all the services that you want to use support temporary security credentials. For a list of the services that accept temporary security credentials, see AWS services that work with IAM in the IAM User Guide.

For more information, see the following related resources in the IAM User Guide: