Fine-grained access control in DynamoDB

Introduction

Fine-grained access control lets you decide exactly who can see or change each piece of data. It helps keep your data safe and private.

When you want users to only see their own data in a shared database.

When different users have different permissions for parts of the data.

When you want to limit access to sensitive information like personal details.

When you want to control who can update or delete specific records.

When you need to follow rules or laws about data privacy.

Syntax

DynamoDB

Use IAM policies with condition keys like dynamodb:LeadingKeys or dynamodb:Attributes to control access.
Example:
{
  "Effect": "Allow",
  "Action": "dynamodb:GetItem",
  "Resource": "arn:aws:dynamodb:region:account-id:table/TableName",
  "Condition": {
    "ForAllValues:StringEquals": {
      "dynamodb:LeadingKeys": ["${aws:username}"]
    }
  }
}

Fine-grained access control is set using IAM policies with special DynamoDB condition keys.

The dynamodb:LeadingKeys condition limits access to items with partition keys matching the user's identity.

Examples

This policy lets a user read only the orders where the partition key matches their username.

DynamoDB

{
  "Effect": "Allow",
  "Action": "dynamodb:GetItem",
  "Resource": "arn:aws:dynamodb:region:account-id:table/Orders",
  "Condition": {
    "ForAllValues:StringEquals": {
      "dynamodb:LeadingKeys": ["${aws:username}"]
    }
  }
}

This policy allows users to update or delete only their own profile data.

DynamoDB

{
  "Effect": "Allow",
  "Action": ["dynamodb:UpdateItem", "dynamodb:DeleteItem"],
  "Resource": "arn:aws:dynamodb:region:account-id:table/Profiles",
  "Condition": {
    "ForAllValues:StringEquals": {
      "dynamodb:LeadingKeys": ["${aws:username}"]
    }
  }
}

Sample Program

This IAM policy allows a user to get items from the Tasks table only if the partition key matches their username. This means users can only read their own tasks.

DynamoDB

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": "dynamodb:GetItem",
      "Resource": "arn:aws:dynamodb:us-west-2:123456789012:table/Tasks",
      "Condition": {
        "ForAllValues:StringEquals": {
          "dynamodb:LeadingKeys": ["${aws:username}"]
        }
      }
    }
  ]
}

Important Notes

Fine-grained access control requires your table's partition key to be designed to support user-based access.

Always test your policies with different users to make sure access is correctly limited.

Summary

Fine-grained access control lets you control access to individual items in DynamoDB tables.

It uses IAM policies with conditions like dynamodb:LeadingKeys to restrict access based on keys.

This helps keep data private and secure for each user.

Practice

1. What is the main purpose of fine-grained access control in DynamoDB?

easy

A. To automatically backup data

B. To speed up query performance

C. To restrict access to specific items based on keys

D. To encrypt data at rest

Solution

1. Step 1: Understand fine-grained access control concept

   Fine-grained access control limits access to individual items or attributes in a DynamoDB table.

2. Step 2: Identify the main purpose

   This control is used to restrict access based on keys, ensuring users see only their data.

3. Final Answer:

   To restrict access to specific items based on keys -> Option C

4. Quick Check:

   Fine-grained access control = restrict by keys [OK]

Hint: Focus on access control by keys, not performance or encryption [OK]

Common Mistakes:

• Confusing access control with encryption
• Thinking it improves query speed
• Assuming it manages backups

2. Which IAM policy condition key is used to enforce fine-grained access control in DynamoDB?

easy

A. dynamodb:LeadingKeys

B. dynamodb:TableName

C. dynamodb:Attributes

D. dynamodb:EncryptionEnabled

Solution

1. Step 1: Identify IAM condition keys for DynamoDB

   DynamoDB uses specific condition keys in IAM policies to control access.

2. Step 2: Match condition key for fine-grained access

   The key dynamodb:LeadingKeys restricts access based on partition key values.

3. Final Answer:

   dynamodb:LeadingKeys -> Option A

4. Quick Check:

   Fine-grained access uses dynamodb:LeadingKeys [OK]

Hint: Remember 'LeadingKeys' controls item-level access [OK]

Common Mistakes:

• Choosing TableName which controls table-level access
• Confusing Attributes with keys
• Selecting unrelated encryption keys

3. Given this IAM policy snippet, which items can the user access?

{
  "Effect": "Allow",
  "Action": "dynamodb:GetItem",
  "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Orders",
  "Condition": {
    "ForAllValues:StringEquals": {
      "dynamodb:LeadingKeys": ["user123"]
    }
  }
}

medium

A. All items in the Orders table

B. Only items with partition key 'user123'

C. Items with any partition key except 'user123'

D. No items, because the policy is invalid

Solution

1. Step 1: Analyze the IAM policy condition

   The condition restricts access to items where the partition key matches 'user123'.

2. Step 2: Determine accessible items

   Only items with partition key 'user123' are accessible; others are denied.

3. Final Answer:

   Only items with partition key 'user123' -> Option B

4. Quick Check:

   Condition limits to 'user123' keys [OK]

Hint: Check the LeadingKeys value to find accessible items [OK]

Common Mistakes:

• Assuming access to all items
• Thinking policy denies all access
• Ignoring the condition block

4. You wrote this IAM policy to restrict access to items with partition key 'user456', but users still access other items:

{
  "Effect": "Allow",
  "Action": "dynamodb:GetItem",
  "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Orders",
  "Condition": {
    "StringEquals": {
      "dynamodb:LeadingKeys": "user456"
    }
  }
}

What is the likely error?

medium

A. Action should be dynamodb:Query instead of GetItem

B. Resource ARN is incorrect

C. Effect should be Deny instead of Allow

D. Condition should use ForAllValues:StringEquals with an array

Solution

1. Step 1: Check condition syntax for dynamodb:LeadingKeys

   The condition expects an array with ForAllValues:StringEquals, not a single string with StringEquals.

2. Step 2: Understand impact of incorrect condition

   Using StringEquals with a string causes the condition to be ignored, allowing broader access.

3. Final Answer:

   Condition should use ForAllValues:StringEquals with an array -> Option D

4. Quick Check:

   Use ForAllValues:StringEquals and array for LeadingKeys [OK]

Hint: Use ForAllValues:StringEquals with array for LeadingKeys [OK]

Common Mistakes:

• Using StringEquals with a string instead of array
• Incorrect ARN format
• Confusing action types
• Changing Effect to Deny unnecessarily

5. You want to allow users to read only their own orders in a DynamoDB table where the partition key is 'UserId'. Which IAM policy condition correctly enforces this fine-grained access control for user 'alice'?

hard

A. { "ForAllValues:StringEquals": { "dynamodb:LeadingKeys": ["alice"] } }

B. { "StringEquals": { "dynamodb:Attributes": ["alice"] } }

C. { "ForAnyValue:StringEquals": { "dynamodb:LeadingKeys": ["alice"] } }

D. { "StringLike": { "dynamodb:LeadingKeys": "alice*" } }

Solution

1. Step 1: Identify correct condition operator for exact key match

   For fine-grained access, ForAllValues:StringEquals with an array ensures all keys match exactly.

2. Step 2: Evaluate options for correct syntax and semantics

   { "ForAllValues:StringEquals": { "dynamodb:LeadingKeys": ["alice"] } } uses correct operator and array format; others use wrong keys or operators.

3. Final Answer:

   { "ForAllValues:StringEquals": { "dynamodb:LeadingKeys": ["alice"] } } -> Option A

4. Quick Check:

   Exact key match needs ForAllValues:StringEquals with array [OK]

Hint: Use ForAllValues:StringEquals with array for exact user keys [OK]

Common Mistakes:

• Using dynamodb:Attributes instead of LeadingKeys
• Using StringEquals without array
• Using StringLike which allows wildcards