Notes and Constraints

Kafka ZooKeeper

Kafka clusters are managed using ZooKeeper. Opening ZooKeeper may cause misoperations and service losses. Currently, ZooKeeper is used only within Kafka clusters and does not provide services externally.

Version

• The service version can be 1.1.0, 2.3.0, or 2.7. Kafka instances cannot be upgraded once they are created.
• Clients later than version 0.10 are supported. Use a version that is consistent with the service version.

Logging in to the VM where the Kafka brokers reside

Not supported

Storage

• The storage space can be expanded but cannot be reduced.
• You can expand the storage space up to 20 times.

Bandwidth or broker quantity

The bandwidth and broker quantity can be increased but cannot be decreased.

VPC, subnet, and AZ

After an instance is created, its VPC, subnet, and AZ cannot be modified.

Kerberos authentication

Not supported

Client connections from each IP address

Each Kafka broker allows a maximum of 1000 connections from each IP address by default. Excess connections will be rejected.

Total number of topic partitions

The total number of topic partitions is related to the instance specifications. For details, see Specifications.

Kafka manages messages by partition. If there are too many partitions, message creation, storage, and retrieval will be fragmented, affecting the performance and stability. If the total number of partitions of topics reaches the upper limit, you cannot create more topics.

Number of partitions in a topic

Based on the open-source Kafka constraints, the number of partitions in a topic can be increased but cannot be decreased.

Topic quantity

The topic quantity is related to the total number of topic partitions and number of partitions in each topic. For details, see Specifications.

Automatic topic creation

Supported. If this option is enabled, a topic will be automatically created when a message is produced in or consumed from a topic that does not exist. By default, the topic has the following parameters:

• Partitions: 3
• Replicas: 3
• Aging Time: 72
• Synchronous Replication and Synchronous Flushing disabled
• Message Timestamp: CreateTime
• Max.Message Size (bytes): 10,485,760

After you change the value of the log.retention.hours, default.replication.factor, or num.partitions parameter, the value will be used in later topics that are automatically created.

For example, assume that num.partitions is changed to 5, an automatically created topic has the following parameters:

• Partitions: 5
• Replicas: 3
• Aging Time: 72
• Synchronous Replication and Synchronous Flushing disabled
• Message Timestamp: CreateTime
• Max.Message Size (bytes): 10,485,760

Synchronous replication

If a topic has only one replica, synchronous replication cannot be enabled.

Replica quantity

Single-replica topics are not recommended. If an instance node is faulty, an internal service error may be reported when you query messages in a topic with only one replica. Therefore, you are not advised to use a topic with only one replica.

Aging time

The value of the log.retention.hours parameter takes effect only if the aging time has not been set for the topic.

For example, if the aging time of Topic01 is set to 60 hours and log.retention.hours is set to 72 hours, the actual aging time of Topic01 is 60 hours.

Batch importing and exporting topics

Batch export is supported, but batch import is not supported.

Topic name

If a topic name starts with a special character, for example, an underscore (_) or a number sign (#), monitoring data cannot be displayed.

Delay queues

Not supported

Broker faults

When some brokers of an instance are faulty, topics cannot be created, modified, or deleted, but can be queried.

Creating consumer groups, consumers, and producers

Consumer groups, consumers, and producers are generated automatically when you use the instance.

Resetting the consumer offset

Messages may be retrieved more than once after the offset is reset.

Consumer group name

If a consumer group name starts with a special character, for example, an underscore (_) or a number sign (#), monitoring data cannot be displayed.

Broker faults

When some instance brokers are faulty, consumer groups cannot be created or deleted, or consumption progress cannot be reset, but consumer groups can be queried.

Message size

The maximum length of a message is 10 MB. If the length exceeds 10 MB, the production fails.

Number of users

The maximum users that can be created for a Kafka instance is 20 or 500. Check the console for the actual limit.

Broker faults

When some instance brokers are faulty, users cannot be created or deleted, or password cannot be reset, but users can be queried.