IAM policies (JSON structure) in AWS - Mini Project: Build & Apply

Create a Basic AWS IAM Policy JSON

📖 Scenario: You are setting up permissions for a new AWS user who needs to read objects from a specific S3 bucket.

🎯 Goal: Build a valid AWS IAM policy in JSON format that allows read-only access to the example-bucket S3 bucket.

📋 What You'll Learn

Create a JSON policy with the correct version

Specify the S3 service in the policy

Allow the action s3:GetObject

Restrict access to the bucket named example-bucket

Use the correct resource ARN format for the bucket objects

💡 Why This Matters

🌍 Real World

IAM policies control who can do what in AWS. Creating correct policies is essential for security and access management.

💼 Career

Cloud engineers and administrators regularly write and manage IAM policies to secure AWS resources.

1

Create the basic IAM policy structure

Create a variable called policy and assign it a dictionary with the key Version set to the string "2012-10-17".

AWS

# Your code here

Hint

The Version key is required in every IAM policy and usually set to "2012-10-17".

2

Add the Statement list with one statement

Add a key Statement to the policy dictionary. Set it to a list containing one dictionary with the key Effect set to "Allow".

AWS

policy = {
    "Version": "2012-10-17",
    # Add Statement list with one statement dictionary
    # Your code here
}

Hint

The Statement key holds a list of permission statements. Each statement needs an Effect key.

3

Specify the Action and Resource in the statement

Inside the statement dictionary in policy["Statement"], add the key Action with the value "s3:GetObject" and the key Resource with the value "arn:aws:s3:::example-bucket/*".

AWS

policy = {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            # Add Action and Resource keys here
            # Your code here
        }
    ]
}

Hint

The Action specifies what is allowed. The Resource specifies which bucket objects are accessible.

4

Complete the IAM policy JSON structure

Ensure the policy dictionary is a complete valid IAM policy JSON with Version, Statement list containing one statement with Effect, Action, and Resource keys as specified.

AWS

policy = {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::example-bucket/*"
        }
    ]
}
# Finalize the policy structure if needed
# Your code here

Hint

Review the entire policy dictionary to confirm it matches the required structure.

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