How Amazon VPC works with IAM - Amazon Virtual Private Cloud

How Amazon VPC works with IAM

Before you use IAM to manage access to Amazon VPC, you should understand what IAM features are available to use with Amazon VPC. To get a high-level view of how Amazon VPC and other AWS services work with IAM, see AWS Services That Work with IAM in the IAM User Guide.

With IAM identity-based policies, you can specify allowed or denied actions. For some actions, you can specify the resources and conditions under which actions are allowed or denied. Amazon VPC supports specific actions, resources, and condition keys. To learn about all of the elements that you use in a JSON policy, see IAM JSON Policy Elements Reference in the IAM User Guide.

Actions

Administrators can use AWS JSON policies to specify who has access to what. That is, which principal can perform actions on what resources, and under what conditions.

The Action element of a JSON policy describes the actions that you can use to allow or deny access in a policy. Policy actions usually have the same name as the associated AWS API operation. There are some exceptions, such as permission-only actions that don't have a matching API operation. There are also some operations that require multiple actions in a policy. These additional actions are called dependent actions.

Include actions in a policy to grant permissions to perform the associated operation.

Amazon VPC shares its API namespace with Amazon EC2. Policy actions in Amazon VPC use the following prefix before the action: ec2:. For example, to grant someone permission to create a VPC with the Amazon EC2 CreateVpc API operation, you include the ec2:CreateVpc action in their policy. Policy statements must include either an Action or NotAction element.

To specify multiple actions in a single statement, separate them with commas as shown in the following example.

"Action": [ "ec2:action1", "ec2:action2" ]

You can specify multiple actions using wildcards (*). For example, to specify all actions that begin with the word Describe, include the following action.

"Action": "ec2:Describe*"

To see a list of Amazon VPC actions, see Actions, Resources, and Condition Keys for Amazon EC2 in the IAM User Guide.

Resources

Administrators can use AWS JSON policies to specify who has access to what. That is, which principal can perform actions on what resources, and under what conditions.

The Resource JSON policy element specifies the object or objects to which the action applies. Statements must include either a Resource or a NotResource element. As a best practice, specify a resource using its Amazon Resource Name (ARN). You can do this for actions that support a specific resource type, known as resource-level permissions.

For actions that don't support resource-level permissions, such as listing operations, use a wildcard (*) to indicate that the statement applies to all resources.

"Resource": "*"
Important

Currently, not all Amazon EC2 API actions support resource-level permissions. If an Amazon EC2 API action does not support resource-level permissions, you can grant users permission to use the action, but you have to specify a * for the resource element of your policy statement. To view the actions for which you can specify an ARN for the resource element, see Actions Defined by Amazon EC2.

The VPC resource has the ARN shown in the following example.

arn:${Partition}:ec2:${Region}:${Account}:vpc/${VpcId}

For more information about the format of ARNs, see Amazon Resource Names (ARNs).

For example, to specify the vpc-1234567890abcdef0 VPC in your statement, use the ARN shown in the following example.

"Resource": "arn:aws:ec2:us-east-1:123456789012:vpc/vpc-1234567890abcdef0"

To specify all VPCs that belong to a specific account, use the wildcard (*).

"Resource": "arn:aws:ec2:us-east-1:123456789012:vpc/*"

Some Amazon VPC actions, such as those for creating resources, cannot be performed on a specific resource. In those cases, you must use the wildcard (*).

"Resource": "*"

Many Amazon EC2 API actions involve multiple resources. To specify multiple resources in a single statement, separate the ARNs with commas.

"Resource": [ "resource1", "resource2" ]

To see a list of Amazon VPC resource types and their ARNs, see Resources Defined by Amazon EC2 in the IAM User Guide.

Condition keys

Administrators can use AWS JSON policies to specify who has access to what. That is, which principal can perform actions on what resources, and under what conditions.

The Condition element (or Condition block) lets you specify conditions in which a statement is in effect. The Condition element is optional. You can create conditional expressions that use condition operators, such as equals or less than, to match the condition in the policy with values in the request.

If you specify multiple Condition elements in a statement, or multiple keys in a single Condition element, AWS evaluates them using a logical AND operation. If you specify multiple values for a single condition key, AWS evaluates the condition using a logical OR operation. All of the conditions must be met before the statement's permissions are granted.

You can also use placeholder variables when you specify conditions. For example, you can grant an IAM user permission to access a resource only if it is tagged with their IAM user name. For more information, see IAM policy elements: variables and tags in the IAM User Guide.

AWS supports global condition keys and service-specific condition keys. To see all AWS global condition keys, see AWS global condition context keys in the IAM User Guide.

Amazon VPC defines its own set of condition keys and also supports using some global condition keys. To see all AWS global condition keys, see AWS Global Condition Context Keys in the IAM User Guide.

All Amazon EC2 actions support the aws:RequestedRegion and ec2:Region condition keys. For more information, see Example: Restricting Access to a Specific Region.

To see a list of Amazon VPC condition keys, see Condition Keys for Amazon EC2 in the IAM User Guide. To learn with which actions and resources you can use a condition key, see Actions Defined by Amazon EC2.

Amazon VPC resource-based policies

Resource-based policies are JSON policy documents that specify what actions a specified principal can perform on the Amazon VPC resource and under what conditions.

To enable cross-account access, you can specify an entire account or IAM entities in another account as the principal in a resource-based policy. Adding a cross-account principal to a resource-based policy is only half of establishing the trust relationship. When the principal and the resource are in different AWS accounts, you must also grant the principal entity permission to access the resource. Grant permission by attaching an identity-based policy to the entity. However, if a resource-based policy grants access to a principal in the same account, no additional identity-based policy is required. For more information, see How IAM Roles Differ from Resource-based Policies in the IAM User Guide.

Authorization based on tags

You can attach tags to Amazon VPC resources or pass tags in a request. To control access based on tags, you provide tag information in the condition element of a policy using the ec2:ResourceTag/key-name, aws:RequestTag/key-name, or aws:TagKeys condition keys. For more information, see Resource-Level Permissions for Tagging in the Amazon EC2 User Guide.

To view an example identity-based policy for limiting access to a resource based on the tags on that resource, see Launching instances into a specific VPC.

IAM roles

An IAM role is an entity within your AWS account that has specific permissions.

Using temporary credentials

You can use temporary credentials to sign in with federation, assume an IAM role, or to assume a cross-account role. You obtain temporary security credentials by calling AWS STS API operations such as AssumeRole or GetFederationToken.

Amazon VPC supports using temporary credentials.

Service-linked roles

Service-linked roles allow AWS services to access resources in other services to complete an action on your behalf. Service-linked roles appear in your IAM account and are owned by the service. An IAM administrator can view but not edit the permissions for service-linked roles.

Transit gateways support service-linked roles.

Service roles

This feature allows a service to assume a service role on your behalf. This role allows the service to access resources in other services to complete an action on your behalf. Service roles appear in your IAM account and are owned by the account. This means that an IAM administrator can change the permissions for this role. However, doing so might break the functionality of the service.

Amazon VPC supports service roles for flow logs. When you create a flow log, you must choose a role that allows the flow logs service to access CloudWatch Logs. For more information, see IAM roles for publishing flow logs to CloudWatch Logs.