AWS Classroom Series – 15/Apr/2021

IAM Policy Grammar

• Refer Here for the official documentation
• Basic policy skeleton

{
    "Version" : "2012-10-17",
    "Statement": [
        {
            "Principal": ,
            "Effect": "Allow|Deny",
            "Action": []
        }
    ]
}

• Lets look at some aws managed policy json
  • Administrator access: Since Action is * and Resource is * i.e. all actions on all resources with Effect Allow
  • ec2readonly:
    • json:

    {
        "Version": "2012-10-17",
        "Statement": [
            {
                "Effect": "Allow",
                "Action": "ec2:Describe*",
                "Resource": "*"
            },
            {
                "Effect": "Allow",
                "Action": "elasticloadbalancing:Describe*",
                "Resource": "*"
            },
            {
                "Effect": "Allow",
                "Action": [
                    "cloudwatch:ListMetrics",
                    "cloudwatch:GetMetricStatistics",
                    "cloudwatch:Describe*"
                ],
                "Resource": "*"
            },
            {
                "Effect": "Allow",
                "Action": "autoscaling:Describe*",
                "Resource": "*"
            }
        ]
    }
    

    • In this case teh actions autoscaling:Describe*, ec2:Describe* and some more read actions are alloweda
• In IAM policy if there is an action which is not specified is denied by default.
• To write the policies effectively we need to know the actions available in AWS
• Refer Here and navigate to topics
• Scenario 1: Lets write an iam policy which gives a principal access on all aws ec2 resources and aws s3 resources
  • ec2 Refer Here. Refer Here for the ec2 actions
  • actions in this page will have a prefix of ec2: for eg: ec2:AttachNetworkInterface, ec2:AttachVolume
  • The resources which we create in ec2 are Refer Here
  • For any resource that can be created in AWS we have a unique ARN (Amazon Resource Name)
  • Refer Here for the policy created
  • Now create an IAM policy using this json
  • For testing policies lets create an iam user with the policy created above attached
  • Login into aws as this test user
    • This user should be able to perform any operations on ec2 and s3
    • When this user tries to access any other service the actions will be denied as the user doesnot have permissions
  • To test iam policies we can use policy simulator Refer Here
  • Navigate to Refer Here
• Scenario 2: Create an IAM policy to perform
  • all the read actions on s3 bucket
  • all the actions on rds
  • Refer Here for the policy and play with policy simulator.