How to create AWS IAM role attaching managed policy only using Boto3

I had a similar question in regard to how to supply the AssumeRolePolicyDocument when creating an IAM role with Boto3.

I used the following code...

assume_role_policy_document = json.dumps({
    "Version": "2012-10-17",
    "Statement": [
        {
        "Effect": "Allow",
        "Principal": {
            "Service": "greengrass.amazonaws.com"
        },
        "Action": "sts:AssumeRole"
        }
    ]
})

create_role_response = self._iam.create_role(
    RoleName = "my-role-name,
    AssumeRolePolicyDocument = assume_role_policy_document
)

Note that the AssumeRolePolicyDocument is about defining the trust relationship and not the actual permissions of the role you are creating.

You would have to create the role (as you are doing above) and then separately attach the managed policy to the role like this:

response = client.attach_role_policy(
    RoleName='MyRole', PolicyArn='<arn of managed policy>')