It’s a global resource, not region-specific.

AWS account root user has extreme power and cannot be limited, so, best practice is:

  • Create IAM admin user
  • Lock away the root user credentials
  • Use IAM admin user

External identity providers

IAM can integrate external identity providers, and attach policies to external entities:

  • Corporate user directory
  • OIDC (Open ID Connect) providers
  • SAML 2.0 identity providers

IAM Principals

A Principal is an entity that can take action on an AWS resource.

IAM Users

  • IAM users are users within your account
  • Each user has his own credentials
  • Authorized to perform specific actions based on its permission
  • No default permissions
  • Access to CLI or Console must be explicitly granted
    (Programmatic access / Management Console access)

IAM Groups

Simply a collection of users (no roles).

The name can be changed, but avoid to do it because also the ARN will change too.

IAM Role

Roles can be used to assign permissions to users or services on a temporary basis.

  • The role is assumed by the user or the service
    • User-based roles
    • Service roles
    • External roles:
      • Cross-account access
      • Federation
  • When you create the role, you specify two policies:
    • The trust policy specifies who is allowed to assume the role (the trusted entity, or principal)
    • The access policy (or permissions policy) defines which actions and resources the principal is allowed to use
  • Use cases:
    • Provide AWS resources access to AWS services
    • Provide access to third parties
    • Provide access to externally authenticated users
    • Switch roles to access resources in your aws account or any other

IAM Policies

  • A policy is an entry that defines permission (attached to an identity or a resource)
  • Any API action is implicitly denied unless there is a policy that explicitly allows it.
  • If there is a policy that explicitly denies an action, that policy always takes precedence.
  • Cannot reach outside AWS
  • Resource-based = Attached to an AWS resource
    • Attached to: aws resources
    • Types: Inline
  • Identity-based = Attached to an IAM principal
    • Attached to: users / group / role
    • Types: AWS-managed / Customer-managed / Inline
      • AWS-managed policies
        created by AWS and managed centrally in IAM
      • Customer-managed policies
        created by the customer and managed centrally in IAM
      • Inline policies
        created by the customer and attached and managed directly at the identity principal
  • A single policy document can have multiple statements (sid field is optional).
  • If the policy is attached to a resource rather than to an IAM identity, then the policy must also specify a principal (to whom the policy applies)

Effect: has the value of either ALLOW or DENY. The entity (whether a user, group, or role) is either granted (or denied) the permission to execute that API.

Action: Action can be an individual API, a grouping of APIs for the same service using a wildcard (for example, S3:* includes all S3 APIs), or APIs for different services.

Resource: You can restrict the policy to a particular object, or particular group of objects (using ARN with the wildcard *).

Use the acronym EAR to remember the three attribute-value pairs

Example Policy 1

Example of a policy to allow read and write access to objects in an S3 Bucket

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "ListObjectsInBucket",
            "Effect": "Allow",
            "Action": ["s3:ListBucket"],
            "Resource": ["arn:aws:s3:::bucket-name"]
        },
        {
            "Sid": "AllObjectActions",
            "Effect": "Allow",
            "Action": "s3:*Object",
            "Resource": ["arn:aws:s3:::bucket-name/*"]
        }
    ]
}

Example Policy 2

Example of a policy to allow a Lambda function access a DynamoDB table

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "ReadWriteTable",
            "Effect": "Allow",
            "Action": [
                "dynamodb:BatchGetItem",
                "dynamodb:GetItem",
                "dynamodb:Query",
                "dynamodb:Scan",
                "dynamodb:BatchWriteItem",
                "dynamodb:PutItem",
                "dynamodb:UpdateItem"
            ],
            "Resource": "arn:aws:dynamodb:*:*:table/SampleTable"
        },
        {
            "Sid": "GetStreamRecords",
            "Effect": "Allow",
            "Action": "dynamodb:GetRecords",
            "Resource": "arn:aws:dynamodb:*:*:table/SampleTable/stream/* "
        },
        {
            "Sid": "WriteLogStreamsAndGroups",
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": "*"
        },
        {
            "Sid": "CreateLogGroup",
            "Effect": "Allow",
            "Action": "logs:CreateLogGroup",
            "Resource": "*"
        }
    ]
}

Applying permissions

  • Attach a policy to an IAM principal
  • A single policy can be attached to multiple entities
  • A single entity can have multiple policies attached to it

ARN

An ARN (Amazon Resource Name) always starts with arn: and can include the following components to identify a particular AWS resource uniquely:

  • Partition Usually aws. For some regions, such as in China, this can have a different value.
  • Service Namespace of the AWS service.
  • Region The region in which the resource is located. Some resources do not require a region to be specified.
  • Account ID The account in which the resource resides. Some resources do not require an account ID to be specified.
  • Resource The specific resource within the namespace of the AWS service. For services that have multiple types of resources, there may also be a resource type.

Examples

Example formats:

arn:partition:service:region:account-id:resource
arn:partition:service:region:account-id:resourcetype/resource
arn:partition:service:region:account-id:resourcetype:resource

Examples of ARNs for various AWS resources:

<!-- Amazon Polly Lexicon -->
arn:aws:polly:us-west-2:123456789012:lexicon/awsLexicon
 
<!-- IAM user name -->
arn:aws:iam::123456789012:user/carla
 
<!-- Object in an Amazon S3 bucket -->
arn:aws:s3:::bucket-name/exampleobject.png
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