Controlling access with AWS Identity and Access Management

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

In addition to AWS CloudFormation 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 AWS CloudFormation. For example, you can specify which users can create Amazon EC2 instances, terminate database instances, or update VPCs. Those same permissions are applied anytime they use AWS CloudFormation to do those actions.

For more information about all the services that you can control access to, see AWS services that support IAM in IAM User Guide.

AWS CloudFormation actions

When you create a group or a user in your AWS account, you can associate an IAM policy with that group or user, which specifies the permissions that you want to grant. For example, imagine you have a group of entry-level developers. You can create a Junior application developers group that includes all entry-level developers. Then, you associate a policy with that group that allows users to only view AWS CloudFormation stacks. In this scenario, you might have a policy such as the following sample:

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

The policy grants permissions to all DescribeStack API actions listed in the Action element.

In addition to AWS CloudFormation actions, users who create or delete stacks require additional permissions that depend on the stack templates. For example, if you have a template that describes an Amazon SQS Queue, the user must have the corresponding permissions for Amazon SQS actions to successfully create the stack, 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":"*"
    }]
}

For a list of all AWS CloudFormation actions that you can allow or deny, see the AWS CloudFormation API Reference.

AWS CloudFormation console-specific actions

Users who use the AWS CloudFormation console require additional permissions that aren't required for using the AWS Command Line Interface or AWS CloudFormation APIs. Compared to the AWS CLI and API, the console provides additional features that require additional permissions, such as template uploads to Amazon S3 buckets and drop-down lists for AWS-specific parameter types.

For all the following actions, grant permissions to all resources; don't limit actions to specific stacks or buckets.

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

cloudformation:CreateUploadBucket

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

s3:PutObject
s3:ListBucket
s3:GetObject
s3:CreateBucket

For templates with AWS-specific parameter types, users need permissions to make the corresponding describe API calls. For example, if a template includes the AWS::EC2::KeyPair::KeyName parameter type, users need permission to call the EC2 DescribeKeyPairs action (this is how the console gets values for the parameter drop-down list). The following examples are actions that users need for other parameter types:

ec2:DescribeSecurityGroups (for the AWS::EC2::SecurityGroup::Id parameter type)
ec2:DescribeSubnets (for the Subnet::Id parameter type)
ec2:DescribeVpcs (for the AWS::EC2::VPC::Id parameter type)

AWS CloudFormation resources

AWS CloudFormation supports resource-level permissions, so you can specify actions for a specific stack, as shown in the following policy:

{
    "Version":"2012-10-17",
    "Statement":[{
        "Effect":"Deny",
        "Action":[
            "cloudformation:DeleteStack",
            "cloudformation:UpdateStack"
        ],
        "Resource":"arn:aws:cloudformation:us-east-1:123456789012: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 the full stack ID (such as arn:aws:cloudformation:us-east-1:123456789012:stack/MyProductionStack/abc9dbf0-43c2-11e3-a6e8-50fa526be49c) and on the stack name (such as MyProductionStack).

To allow AWS::Serverless transforms to create a change set, the policy should 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:us-west-2:aws:transform/Serverless-2016-10-31"
    }]
}

Sample policy that grants service-managed stack set permissions

The following is a sample IAM policy that grants service-managed stack set permissions to a principal entity (user, role, or group). A user with this policy can only perform operations on stack sets with templates containing Amazon S3 resource types (AWS::S3::*) or the AWS::SES::ConfigurationSet resource type. If signed in to the organization management account with ID 123456789012, the user can also only perform operations on stack sets that target the OU with ID ou-1fsfsrsdsfrewr, and can only perform operations on the stack set with ID stack-set-id that targets the AWS account with ID 987654321012.

Stack set operations fail if the stack set template contains resource types other than those specified in the policy, or if the deployment targets are OU or account IDs other than those specified in the policy for the corresponding management accounts and stack sets.

These policy restrictions only apply when stack set operations target the us-east-1, us-west-2, or eu-west-2 AWS Regions.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "cloudformation:*"
            ],
            "Resource": [
                "arn:aws:cloudformation:*:*:stackset/*",
                "arn:aws:cloudformation:*:*:type/resource/AWS-S3-*",
                "arn:aws:cloudformation:us-west-2::type/resource/AWS-SES-ConfigurationSet",
                "arn:aws:cloudformation:*:123456789012:stackset-target/*/ou-1fsfsrsdsfrewr",
                "arn:aws:cloudformation:*:123456789012:stackset-target/stack-set-id/987654321012"
            ],
            "Condition": {
                "ForAllValues:StringEqualsIgnoreCase": {
                    "cloudformation:TargetRegion": [
                        "us-east-1",
                        "us-west-2",
                        "eu-west-1"
                    ]
                }
            }
        }
    ]
}

AWS CloudFormation conditions

In an IAM policy, 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 AWS 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 AWS CloudFormation-specific conditions. These conditions are applied only when users create or update stacks:

Examples

The following example policy allows users to use only the https://s3.amazonaws.com/testbucket/test.template template URL to create or update a stack.

{
  "Version":"2012-10-17",
  "Statement":[
    {
      "Effect" : "Allow",
      "Action" : [ "cloudformation:CreateStack", "cloudformation:UpdateStack" ],
      "Resource" : "*",
      "Condition" : {
        "StringEquals" : {
          "cloudformation:TemplateUrl" : [ "https://s3.amazonaws.com/testbucket/test.template" ]
        }
      }
    }
  ]
}

The following example policy allows users to complete all AWS CloudFormation operations except import operations.

{ 
  "Version": "2012-10-17", 
  "Statement": [ 
    { 
      "Sid": "AllowAllStackOperations",
      "Effect": "Allow", 
      "Action": "cloudformation:*", 
      "Resource": "*" 
    }, 
    { 
      "Sid": "DenyImport", 
      "Effect": "Deny", 
      "Action": "cloudformation:*", 
      "Resource": "*",
      "Condition": { 
        "ForAnyValue:StringLike": {
          "cloudformation:ImportResourceTypes": [ 
            "*" 
          ] 
        } 
      } 
    } 
  ] 
}

The following example policy allows all stack operations, in addition to import operations only on specified resources (in this example, AWS::S3::Bucket.

{ 
  "Version": "2012-10-17", 
  "Statement": [ 
    { 
      "Sid": "AllowImport",
      "Effect": "Allow", 
      "Action": "cloudformation:*", 
      "Resource": "*" 
      "Condition": { 
        "ForAllValues:StringEqualsIgnoreCase": {
          "cloudformation:ImportResourceTypes": [ 
            "AWS::S3::Bucket" 
          ] 
        } 
      } 
    } 
  ] 
}

The following example policy allows users to create stacks but denies requests if the stack's template include any resource from the IAM service. The policy also requires users to specify the ResourceTypes parameter, which is available only for AWS CLI and API requests. This policy uses explicit deny statements so that if any other policy grants additional permissions, this policy always remain in effect (an explicit deny statement always overrides an explicit allow statement).

{
  "Version":"2012-10-17",
  "Statement":[
    {
      "Effect" : "Allow",
      "Action" : [ "cloudformation:CreateStack" ],
      "Resource" : "*"
    },
    {
      "Effect" : "Deny",
      "Action" : [ "cloudformation:CreateStack" ],
      "Resource" : "*",
      "Condition" : {
        "ForAnyValue:StringLikeIfExists" : {
          "cloudformation:ResourceTypes" : [ "AWS::IAM::*" ]
        }
      }
    },
    {
      "Effect": "Deny",
      "Action" : [ "cloudformation:CreateStack" ],
      "Resource": "*",
      "Condition": {
        "Null": {
          "cloudformation:ResourceTypes": "true"
        }
      }
    }
  ]
}

The following example policy is similar to the preceding example. The policy allows users to create a stack unless the stack's template includes any resource from the IAM service. It also requires users to specify the ResourceTypes parameter, which is available only for AWS CLI and API requests. This policy is simpler, but it doesn't use explicit deny statements. Other policies, granting additional permissions, could override this policy.

{
  "Version":"2012-10-17",
  "Statement":[
    {
      "Effect" : "Allow",
      "Action" : [ "cloudformation:CreateStack" ],
      "Resource" : "*",
      "Condition" : {
        "ForAllValues:StringNotLikeIfExists" : {
          "cloudformation:ResourceTypes" : [ "AWS::IAM::*" ]
        },
        "Null":{
          "cloudformation:ResourceTypes": "false"
        }
      }
    }
  ]
}

Acknowledging IAM resources in AWS CloudFormation templates

Before you can create a stack, AWS CloudFormation validates your template. During validation, AWS 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 AWS CloudFormation the specified capabilities before it creates the stack.

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

Manage 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.

Grant 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 AWS 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 Ways to get temporary security credentials in Using Temporary Security Credentials.

AWS CloudFormation interacts with many other AWS services. When you use temporary security credentials with AWS CloudFormation, verify that all the services that you want to use support temporary security credentials. For more information, see AWS services that support AWS STS.

For more information, see the following related resources in Using Temporary Security Credentials: