Manage IAM roles using an Amazon SDK

Create functions that wrap IAM role actions.

import json
import logging
import pprint

import boto3
from botocore.exceptions import ClientError

logger = logging.getLogger(__name__)
iam = boto3.resource("iam")

def create_role(role_name, allowed_services):
    """
    Creates a role that lets a list of specified services assume the role.

    :param role_name: The name of the role.
    :param allowed_services: The services that can assume the role.
    :return: The newly created role.
    """
    trust_policy = {
        "Version": "2012-10-17",
        "Statement": [
            {
                "Effect": "Allow",
                "Principal": {"Service": service},
                "Action": "sts:AssumeRole",
            }
            for service in allowed_services
        ],
    }

    try:
        role = iam.create_role(
            RoleName=role_name, AssumeRolePolicyDocument=json.dumps(trust_policy)
        )
        logger.info("Created role %s.", role.name)
    except ClientError:
        logger.exception("Couldn't create role %s.", role_name)
        raise
    else:
        return role



def attach_policy(role_name, policy_arn):
    """
    Attaches a policy to a role.

    :param role_name: The name of the role. **Note** this is the name, not the ARN.
    :param policy_arn: The ARN of the policy.
    """
    try:
        iam.Role(role_name).attach_policy(PolicyArn=policy_arn)
        logger.info("Attached policy %s to role %s.", policy_arn, role_name)
    except ClientError:
        logger.exception("Couldn't attach policy %s to role %s.", policy_arn, role_name)
        raise



def detach_policy(role_name, policy_arn):
    """
    Detaches a policy from a role.

    :param role_name: The name of the role. **Note** this is the name, not the ARN.
    :param policy_arn: The ARN of the policy.
    """
    try:
        iam.Role(role_name).detach_policy(PolicyArn=policy_arn)
        logger.info("Detached policy %s from role %s.", policy_arn, role_name)
    except ClientError:
        logger.exception(
            "Couldn't detach policy %s from role %s.", policy_arn, role_name
        )
        raise



def delete_role(role_name):
    """
    Deletes a role.

    :param role_name: The name of the role to delete.
    """
    try:
        iam.Role(role_name).delete()
        logger.info("Deleted role %s.", role_name)
    except ClientError:
        logger.exception("Couldn't delete role %s.", role_name)
        raise

Use the wrapper functions to create a role, then attach and detach a policy.

def usage_demo():
    """Shows how to use the role functions."""
    logging.basicConfig(level=logging.INFO, format="%(levelname)s: %(message)s")
    print("-" * 88)
    print("Welcome to the AWS Identity and Account Management role demo.")
    print("-" * 88)
    print(
        "Roles let you define sets of permissions and can be assumed by "
        "other entities, like users and services."
    )
    print("The first 10 roles currently in your account are:")
    roles = list_roles(10)
    print(f"The inline policies for role {roles[0].name} are:")
    list_policies(roles[0].name)
    role = create_role(
        "demo-iam-role", ["lambda.amazonaws.com", "batchoperations.s3.amazonaws.com"]
    )
    print(f"Created role {role.name}, with trust policy:")
    pprint.pprint(role.assume_role_policy_document)
    policy_arn = "arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess"
    attach_policy(role.name, policy_arn)
    print(f"Attached policy {policy_arn} to {role.name}.")
    print(f"Policies attached to role {role.name} are:")
    list_attached_policies(role.name)
    detach_policy(role.name, policy_arn)
    print(f"Detached policy {policy_arn} from {role.name}.")
    delete_role(role.name)
    print(f"Deleted {role.name}.")
    print("Thanks for watching!")