IAM policies (JSON structure) in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an IAM policy in AWS?

An IAM policy is a JSON document that defines permissions for AWS resources. It tells who can do what on which resource.

beginner

What are the main parts of an IAM policy JSON?

The main parts are:
1. Version - policy language version
2. Statement - list of permission rules
3. Effect - Allow or Deny
4. Action - what actions are allowed or denied
5. Resource - which AWS resources the policy applies to

beginner

What does the 'Effect' field in an IAM policy specify?

The 'Effect' field specifies whether the policy allows or denies the actions. It can be either 'Allow' or 'Deny'.

beginner

How do you specify multiple actions in an IAM policy?

You list multiple actions as an array of strings under the 'Action' field, for example: ["s3:GetObject", "s3:PutObject"].

beginner

What is the purpose of the 'Resource' field in an IAM policy?

The 'Resource' field specifies which AWS resources the policy applies to, using ARNs (Amazon Resource Names).

Which field in an IAM policy JSON defines whether to allow or deny permissions?

A Effect

B Action

C Resource

D Version

The 'Effect' field specifies if the policy allows or denies the actions.

What type of document format is used for IAM policies?

A YAML

B JSON

C XML

D CSV

IAM policies are written in JSON format.

In an IAM policy, where do you list the AWS actions you want to allow or deny?

A Effect

B Resource

C Action

D Statement

The 'Action' field lists the AWS actions the policy controls.

What does the 'Version' field in an IAM policy specify?

A The AWS service version

B The resource version

C The user version

D The policy language version

The 'Version' field specifies the version of the policy language.

Which of the following is a valid 'Effect' value in an IAM policy?

A Allow

B Authorize

C Grant

D Permit

'Allow' is the correct value to permit actions in IAM policies.

Describe the structure of an AWS IAM policy JSON document.

Think about the main parts that define permissions.

Explain how you would allow a user to read objects from a specific S3 bucket using an IAM policy.

Focus on the Effect, Action, and Resource fields.

Practice

1. What is the main purpose of an IAM policy in AWS?

easy

A. To create virtual machines

B. To define permissions for users and resources

C. To monitor network traffic

D. To store data in the cloud

Solution

1. Step 1: Understand IAM policy role

   An IAM policy is a JSON document that specifies permissions for AWS users, groups, or roles.

2. Step 2: Identify main function

   Its main function is to control what actions are allowed or denied on AWS resources.

3. Final Answer:

   To define permissions for users and resources -> Option B

4. Quick Check:

   IAM policy = permissions definition [OK]

Hint: IAM policies control access permissions in AWS [OK]

Common Mistakes:

• Confusing IAM policies with data storage
• Thinking IAM policies monitor network traffic
• Assuming IAM policies create virtual machines

2. Which of the following is the correct JSON key to specify the effect of a statement in an IAM policy?

easy

A. "Permission"

B. "Action"

C. "Resource"

D. "Effect"

Solution

1. Step 1: Recall IAM policy statement keys

   IAM policy statements include keys like Effect, Action, Resource, and optionally Condition.

2. Step 2: Identify key for permission type

   The key that specifies whether to allow or deny is "Effect".

3. Final Answer:

   "Effect" -> Option D

4. Quick Check:

   Effect key = permission type [OK]

Hint: Effect key sets allow or deny in IAM policy [OK]

Common Mistakes:

• Using "Permission" instead of "Effect"
• Confusing "Action" with permission type
• Mistaking "Resource" for effect

3. Given this IAM policy statement snippet:

{
  "Effect": "Allow",
  "Action": "s3:ListBucket",
  "Resource": "arn:aws:s3:::example-bucket"
}

What permission does this statement grant?

medium

A. Allows listing the bucket itself

B. Allows listing objects inside the bucket

C. Allows deleting the bucket

D. Allows uploading objects to the bucket

Solution

1. Step 1: Understand the Action "s3:ListBucket"

   This action allows listing the bucket itself and its metadata, not the objects inside.

2. Step 2: Match Resource and Action

   The resource is the bucket ARN, so permission is to list the bucket (its properties), not the objects inside the bucket.

3. Final Answer:

   Allows listing the bucket itself -> Option A

4. Quick Check:

   s3:ListBucket = list bucket (not objects) [OK]

Hint: s3:ListBucket lists the bucket, not objects inside [OK]

Common Mistakes:

• Confusing ListBucket with listing objects inside the bucket
• Assuming permission to delete or upload
• Ignoring the resource ARN level

4. Identify the error in this IAM policy statement:

{
  "Effect": "Allow",
  "Action": ["ec2:StartInstances", "ec2:StopInstances"],
  "Resource": "*",
  "Condition": {
    "StringEquals": {
      "ec2:Region": "us-west-2"
    }
  }
}

medium

A. The Condition key is not valid for EC2 actions

B. The Condition key should be inside the Action key

C. The policy is valid and has no errors

D. The Resource value "*" is not allowed for these actions

Solution

1. Step 1: Check Condition usage with EC2 actions

   EC2 supports conditions like StringEquals on ec2:Region to restrict actions by region.

2. Step 2: Verify Resource and structure

   Resource "*" is valid for EC2 start/stop actions because they apply to instances across resources.

3. Final Answer:

   The policy is valid and has no errors -> Option C

4. Quick Check:

   Condition on ec2:Region with Resource "*" is valid [OK]

Hint: Conditions can restrict actions by region or other keys [OK]

Common Mistakes:

• Thinking Condition is invalid for EC2
• Assuming Resource "*" is always wrong
• Misplacing Condition inside Action

5. You want to create an IAM policy that allows a user to read objects only from a specific S3 bucket named "my-data-bucket" but denies deleting any objects. Which policy statement correctly achieves this?

hard

A. {
"Effect": "Allow",
"Action": ["s3:GetObject"],
"Resource": "arn:aws:s3:::my-data-bucket/*"
}

B. {
"Effect": "Allow",
"Action": ["s3:GetObject", "s3:DeleteObject"],
"Resource": "arn:aws:s3:::my-data-bucket/*"
}

C. {
"Effect": "Deny",
"Action": "s3:DeleteObject",
"Resource": "arn:aws:s3:::my-data-bucket/*"
}

D. {
"Effect": "Allow",
"Action": "s3:*",
"Resource": "arn:aws:s3:::my-data-bucket"
}

Solution

1. Step 1: Identify required permissions

   The user needs permission to read objects only, which is "s3:GetObject" on the bucket's objects.

2. Step 2: Check for delete denial

   Not including "s3:DeleteObject" means no delete permission is granted. Explicit deny is not required if no allow exists.

3. Step 3: Validate resource ARN

   The resource must include "/*" to specify objects inside the bucket, not the bucket itself.

4. Final Answer:

   Allow s3:GetObject on objects in my-data-bucket only -> Option A

5. Quick Check:

   Allow read only, no delete = { "Effect": "Allow", "Action": ["s3:GetObject"], "Resource": "arn:aws:s3:::my-data-bucket/*" } [OK]

Hint: Allow only needed actions; omit delete to deny it [OK]

Common Mistakes:

• Allowing delete by mistake
• Using bucket ARN without /* for objects
• Using wildcard s3:* granting too many permissions