IAM policy for DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an IAM policy in AWS?

An IAM policy is a set of rules that define what actions are allowed or denied on AWS resources for users or roles.

beginner

Which AWS service does the IAM policy control in this topic?

The IAM policy controls access to DynamoDB, which is a NoSQL database service.

beginner

What is the purpose of the "Action" field in an IAM policy for DynamoDB?

The "Action" field specifies which DynamoDB operations (like reading or writing data) are allowed or denied.

intermediate

Why is it important to specify the "Resource" in an IAM policy?

Specifying the "Resource" limits the policy to certain DynamoDB tables or indexes, improving security by not allowing access to everything.

beginner

What does the "Effect" field in an IAM policy do?

The "Effect" field determines whether the policy allows or denies the specified actions on the resources.

Which IAM policy "Effect" value allows access to DynamoDB actions?

A Ignore

B Allow

C Deny

D Block

The "Allow" effect grants permission to perform the specified actions.

What does the "Resource" field in a DynamoDB IAM policy specify?

A The AWS region

B The password

C The user name

D The DynamoDB table or index to access

The "Resource" field limits the policy to specific DynamoDB tables or indexes.

Which of these is a valid DynamoDB action in an IAM policy?

A s3:PutObject

B ec2:StartInstances

C dynamodb:PutItem

D lambda:InvokeFunction

"dynamodb:PutItem" is an action to add or replace an item in a DynamoDB table.

If you want to deny all access to DynamoDB, what should the "Effect" be?

A Deny

B Allow

C Block

D Reject

The "Deny" effect explicitly blocks the specified actions.

Why should IAM policies be as specific as possible?

A To improve security by limiting access

B To make policies easier to read

C To allow all users full access

D To speed up AWS services

Specific policies reduce risk by granting only the needed permissions.

Explain the key components of an IAM policy for DynamoDB and their roles.

Think about what each part controls: allow or deny, what actions, and on which tables.

Describe why it is important to limit IAM policy permissions when working with DynamoDB.

Consider what could happen if permissions are too broad.

Practice

1. What does the Action element specify in an IAM policy for DynamoDB?

easy

A. The allowed or denied DynamoDB operations

B. The AWS region where the table is located

C. The encryption method used by the table

D. The billing mode of the DynamoDB table

Solution

1. Step 1: Understand the role of Action in IAM policies

   The Action element defines which DynamoDB operations (like read, write) are allowed or denied.

2. Step 2: Differentiate from other policy elements

   Other elements like Resource specify the table, but Action controls what can be done.

3. Final Answer:

   The allowed or denied DynamoDB operations -> Option A

4. Quick Check:

   Action = Allowed/Deny operations [OK]

Hint: Action controls what operations are allowed or denied [OK]

Common Mistakes:

• Confusing Action with Resource
• Thinking Action specifies table location
• Mixing Action with encryption or billing settings

2. Which of the following is the correct syntax to specify a DynamoDB table resource ARN in an IAM policy?

easy

A. "Resource": "arn:aws:s3:::mybucket"

B. "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/MyTable"

C. "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table"

D. "Resource": "arn:aws:dynamodb:us-east-1:123456789012:database/MyTable"

Solution

1. Step 1: Identify correct ARN format for DynamoDB table

   The ARN format for a DynamoDB table is: arn:aws:dynamodb:<region>::table/.

2. Step 2: Compare options to the correct format

   "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/MyTable" matches the correct format exactly. "Resource": "arn:aws:s3:::mybucket" is for S3, C misses table name, D uses wrong resource type.

3. Final Answer:

   "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/MyTable" -> Option B

4. Quick Check:

   Resource ARN for DynamoDB table = "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/MyTable" [OK]

Hint: DynamoDB table ARN ends with 'table/YourTableName' [OK]

Common Mistakes:

• Using S3 ARN format instead of DynamoDB
• Omitting the table name in ARN
• Using 'database' instead of 'table' in ARN

3. Given this IAM policy snippet, what DynamoDB actions are allowed?

{
  "Effect": "Allow",
  "Action": ["dynamodb:GetItem", "dynamodb:Query"],
  "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Orders"
}

medium

A. Full access to all DynamoDB tables

B. Writing and deleting items in the Orders table

C. Only reading items from the Orders table

D. No access because the policy is incomplete

Solution

1. Step 1: Analyze the Action list in the policy

   The policy allows only "dynamodb:GetItem" and "dynamodb:Query", which are read operations.

2. Step 2: Check the Resource and Effect

   The resource is the Orders table only, and Effect is Allow, so only reading from Orders is allowed.

3. Final Answer:

   Only reading items from the Orders table -> Option C

4. Quick Check:

   Allowed actions = GetItem and Query (read) [OK]

Hint: GetItem and Query mean read-only access [OK]

Common Mistakes:

• Assuming write or delete permissions are included
• Thinking policy applies to all tables
• Ignoring the Effect value

4. You wrote this IAM policy but it does not allow any access to your DynamoDB table. What is the error?

{
  "Effect": "Allow",
  "Action": "dynamodb:PutItem",
  "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table"
}

medium

A. Resource ARN is incomplete; missing table name

B. Action should be an array, not a string

C. Effect should be Deny to allow access

D. Policy is missing a Condition block

Solution

1. Step 1: Check the Resource ARN format

   The ARN ends with 'table' but does not specify the table name, so it does not point to any specific table.

2. Step 2: Understand impact of incomplete ARN

   Without a full ARN including the table name, the policy does not grant access to any resource.

3. Final Answer:

   Resource ARN is incomplete; missing table name -> Option A

4. Quick Check:

   Resource ARN must include table name [OK]

Hint: Resource ARN must specify full table name [OK]

Common Mistakes:

• Thinking Action must be an array always
• Confusing Effect Allow with Deny
• Assuming Condition is required for access

5. You want to create an IAM policy that allows a user to read from any DynamoDB table in your account but only write to a specific table named 'Inventory'. Which policy setup is correct?

hard

A. { "Effect": "Allow", "Action": ["dynamodb:PutItem"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/*" }, { "Effect": "Allow", "Action": ["dynamodb:GetItem", "dynamodb:Query"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Inventory" }

B. { "Effect": "Allow", "Action": ["dynamodb:GetItem", "dynamodb:Query", "dynamodb:PutItem"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/*" }

C. { "Effect": "Allow", "Action": "dynamodb:*", "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Inventory" }

D. { "Effect": "Allow", "Action": ["dynamodb:GetItem", "dynamodb:Query"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/*" }, { "Effect": "Allow", "Action": ["dynamodb:PutItem"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Inventory" }

Solution

1. Step 1: Identify read permissions scope

   Read actions (GetItem, Query) should apply to all tables, so Resource uses wildcard '*'.

2. Step 2: Identify write permissions scope

   Write action (PutItem) is limited to the 'Inventory' table only.

3. Step 3: Match policy statements to requirements

   { "Effect": "Allow", "Action": ["dynamodb:GetItem", "dynamodb:Query"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/*" }, { "Effect": "Allow", "Action": ["dynamodb:PutItem"], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Inventory" } correctly separates read and write permissions with proper Resource ARNs.

4. Final Answer:

   Separate statements: read on all tables, write only on Inventory -> Option D

5. Quick Check:

   Read = all tables, Write = Inventory only [OK]

Hint: Use separate statements for different resource scopes [OK]

Common Mistakes:

• Granting write access to all tables
• Mixing read and write on wrong resources
• Using wildcard for write when not intended