ACL-based authorization in Kafka - Commands & Configuration

Introduction

Kafka ACL-based authorization controls who can read, write, or manage Kafka resources. It helps keep your Kafka data safe by allowing only trusted users to perform specific actions.

When you want to allow only certain users to produce messages to a topic.

When you want to restrict who can consume messages from a topic.

When you need to control who can create or delete topics.

When you want to secure Kafka clusters in a multi-tenant environment.

When you want to audit and manage permissions centrally.

Config File - server.properties

server.properties

authorizer.class.name=kafka.security.auth.SimpleAclAuthorizer
super.users=User:admin

# Enable ACLs
allow.everyone.if.no.acl.found=false

# Enable SASL for authentication
security.inter.broker.protocol=SASL_PLAINTEXT
sasl.mechanism.inter.broker.protocol=PLAIN
listeners=SASL_PLAINTEXT://:9092
sasl.enabled.mechanisms=PLAIN

This configuration enables ACL-based authorization using Kafka's SimpleAclAuthorizer.

authorizer.class.name: Enables ACL checks.

super.users: Defines admin users who bypass ACLs.

allow.everyone.if.no.acl.found: Denies access if no ACL is found.

security.inter.broker.protocol and related settings enable SASL authentication for secure communication.

Commands

This command adds an ACL to allow user 'alice' to read messages from the topic 'my-topic'.

Terminal

kafka-acls --authorizer-properties zookeeper.connect=localhost:2181 --add --allow-principal User:alice --operation Read --topic my-topic

Expected Output

Added ACLs for resource `Topic:my-topic` for principal User:alice

→

--add - Add a new ACL rule

→

--allow-principal - Specify the user allowed

→

--operation - Specify the allowed action

This command lists all ACLs set on the topic 'my-topic' so you can verify permissions.

Terminal

kafka-acls --authorizer-properties zookeeper.connect=localhost:2181 --list --topic my-topic

Expected Output

Current ACLs for resource `Topic:my-topic`:

  User:alice has Read permission

→

--list - List existing ACLs

→

--topic - Specify the topic to check

This command removes the ACL that allowed user 'alice' to read from 'my-topic'.

Terminal

kafka-acls --authorizer-properties zookeeper.connect=localhost:2181 --remove --allow-principal User:alice --operation Read --topic my-topic

Expected Output

Removed ACLs for resource `Topic:my-topic` for principal User:alice

→

--remove - Remove an existing ACL rule

→

--allow-principal - Specify the user to remove permission for

→

--operation - Specify the action to remove

Key Concept

If you remember nothing else from this pattern, remember: ACLs explicitly grant or deny user permissions on Kafka resources to secure access.

Common Mistakes

Not specifying the correct principal format like User:username

Kafka requires the principal to be in the format User:username to match ACLs correctly.

Always use the full principal format, for example, User:alice.

Forgetting to enable the authorizer.class.name in server.properties

Without enabling the authorizer, Kafka ignores ACLs and allows all access.

Set authorizer.class.name=kafka.security.auth.SimpleAclAuthorizer in server.properties.

Using --add without specifying the resource like --topic or --group

Kafka needs to know which resource the ACL applies to; missing this causes errors.

Always specify the resource with flags like --topic my-topic or --group my-group.

Summary

Configure Kafka server.properties to enable ACL-based authorization and authentication.

Use kafka-acls CLI commands to add, list, and remove ACLs for users on topics.

Always specify the full principal and resource when managing ACLs to avoid errors.

Practice

1. What is the main purpose of ACL-based authorization in Kafka?

easy

A. To control who can access Kafka topics and perform operations

B. To speed up message processing in Kafka

C. To store messages in a compressed format

D. To monitor Kafka cluster health

Solution

1. Step 1: Understand ACL-based authorization

   ACL-based authorization is used to manage permissions for users or clients in Kafka.

2. Step 2: Identify its main role

   Its main role is to control access to Kafka topics and operations, ensuring security.

3. Final Answer:

   To control who can access Kafka topics and perform operations -> Option A

4. Quick Check:

   ACL controls access = B [OK]

Hint: ACL means controlling access rights in Kafka [OK]

Common Mistakes:

• Confusing ACL with performance tuning
• Thinking ACL compresses data
• Assuming ACL monitors cluster health

2. Which of the following is the correct command to add an ACL for a user named alice to read from topic orders?

easy

A. kafka-acls --add --allow-principal User:alice --operation Read --topic orders

B. kafka-acls --remove --allow-principal User:alice --operation Read --topic orders

C. kafka-acls --add --deny-principal User:alice --operation Write --topic orders

D. kafka-acls --add --allow-principal User:bob --operation Read --topic orders

Solution

1. Step 1: Identify the command to add ACL

   The command to add an ACL uses --add and specifies the principal and operation.

2. Step 2: Match user, operation, and topic

   We want to add read permission for user alice on topic orders, so the command must include these exactly.

3. Final Answer:

   kafka-acls --add --allow-principal User:alice --operation Read --topic orders -> Option A

4. Quick Check:

   Add ACL for alice to read orders = D [OK]

Hint: Add ACL uses --add and --allow-principal [OK]

Common Mistakes:

• Using --remove instead of --add
• Using deny instead of allow
• Specifying wrong user or operation

3. Given the following ACLs:

kafka-acls --add --allow-principal User:bob --operation Write --topic payments
kafka-acls --add --allow-principal User:bob --operation Read --topic payments

What will happen if user bob tries to consume messages from topic payments?

medium

A. Bob can only produce messages but not consume

B. Bob will get a permission denied error when consuming messages

C. Bob can neither produce nor consume messages

D. Bob will be able to consume messages from the payments topic

Solution

1. Step 1: Analyze the ACLs for user bob

   Bob has both Write and Read permissions on the payments topic.

2. Step 2: Understand consuming messages requires Read permission

   Since Bob has Read permission, he can consume messages from the payments topic.

3. Final Answer:

   Bob will be able to consume messages from the payments topic -> Option D

4. Quick Check:

   Read permission allows consume = C [OK]

Hint: Read permission lets user consume messages [OK]

Common Mistakes:

• Assuming Write permission alone allows consuming
• Confusing produce and consume permissions
• Ignoring the Read permission present

4. You run the command:

kafka-acls --add --allow-principal User:carol --operation Read --topic sales

But Carol still cannot read from the sales topic. What is the most likely cause?

medium

A. The ACL was added but the Kafka broker was not restarted

B. Carol needs Write permission to read messages

C. Carol's client is not authenticating as User:carol

D. The ACL was added for the wrong user

Solution

1. Step 1: Check if ACL command syntax is correct

   The command correctly adds Read permission for User:carol on topic sales.

2. Step 2: Consider authentication and identity

   If Carol cannot read despite ACL, likely her client is not authenticating as User:carol, so ACL does not apply.

3. Final Answer:

   Carol's client is not authenticating as User:carol -> Option C

4. Quick Check:

   ACL needs matching user identity = A [OK]

Hint: ACLs depend on correct user authentication [OK]

Common Mistakes:

• Thinking Write permission is needed to read
• Assuming Kafka broker restart is required for ACL changes
• Confusing user names in ACL commands

5. You want to allow a group of users to produce messages to topic logs but deny them from deleting the topic. Which ACL commands correctly achieve this?

hard

A. Add allow ACL for Produce operation only; deny is not needed because deny is default

B. Add allow ACL for Produce operation and add deny ACL for Delete operation for the user group

C. Add allow ACL for Produce and Delete operations for the user group

D. Add deny ACL for Produce and allow ACL for Delete operations for the user group

Solution

1. Step 1: Understand permission requirements

   The users should be allowed to produce messages but denied from deleting the topic.

2. Step 2: Use allow and deny ACLs appropriately

   We add an allow ACL for Produce operation and explicitly add a deny ACL for Delete operation to prevent deletion.

3. Final Answer:

   Add allow ACL for Produce operation and add deny ACL for Delete operation for the user group -> Option B

4. Quick Check:

   Allow produce + deny delete = A [OK]

Hint: Use allow for produce and deny for delete explicitly [OK]

Common Mistakes:

• Assuming deny is default without adding deny ACL
• Allowing delete by mistake
• Mixing up allow and deny commands