Kafka Data Migration Overview

Scenario

You can migrate Kafka services to connect message producers and consumers to a new Kafka instance and can even migrate persisted message data to the new Kafka instance. Kafka services can be migrated in the following two scenarios:

• Migrating services to the cloud without downtime

  Services that have high requirements on continuity must be smoothly migrated to the cloud because they cannot afford a long downtime.

• Re-deploying services on the cloud

  A Kafka instance deployed within an AZ is not capable of cross-AZ disaster recovery. For higher reliability, you can re-deploy services to an instance that is deployed across AZs.

Preparation

1. Configure the network environment.

   To connect to a Kafka instance in a private network, configure a security group with parameters specified as follows.

   Table 1 Security group rules

   Direction	Protocol	Port	Source	Description
   Inbound	Select TCP.	9092	0.0.0.0/0	Access a Kafka instance within a VPC (without SSL). Access a Kafka instance across VPCs using a peering connection (without SSL).
   Inbound	Select TCP.	9093	0.0.0.0/0	Access a Kafka instance within a VPC (with SSL). Access a Kafka instance across VPCs using a peering connection (with SSL).

2. Create a Kafka instance.

   The specifications of the new instance cannot be lower than the original specifications. For more information, see Buying a Kafka Instance.

3. Create a topic.

   Create a topic with the same configurations as the original Kafka instance, including the topic name, number of replicas, number of partitions, message aging time, and whether to enable synchronous replication and flushing. For more information, see Creating a Kafka Topic.

Migration Scheme 1: Migrating the Production First

Migrate the message production service to the new Kafka instance. After migration, the original Kafka instance will no longer produce messages. After all messages of the original Kafka instance are consumed, migrate the message consumption service to the new Kafka instance to consume messages of this instance.

1. Change the Kafka connection address of the producer to that of the new Kafka instance.
2. Restart the production service so that the producer can send new messages to the new Kafka instance.
3. Check the consumption progress of each consumer group in the original Kafka instance until all data in the original Kafka instance is consumed.
4. Change the Kafka connection addresses of the consumers to those of the new Kafka instance.
5. Restart the consumption service so that consumers can consume messages from the new Kafka instance.
6. Check whether consumers consume messages properly from the new Kafka instance.
7. The migration is complete.

This is a common migration scheme. It is simple and easy to control on the service side. During the migration, the message sequence is ensured, so this scheme is suitable for scenarios with strict requirements on the message sequence. However, latency may occur because there is a period when you have to wait for all data to be consumed.

Migration Scheme 2: Migrating the Production Later

Use multiple consumers for the consumption service. Some consume messages from the original Kafka instance, and others consume messages from the new Kafka instances. Then, migrate the production service to the new Kafka instance so that all messages can be consumed in time.

1. Start new consumer clients, set the Kafka connection addresses to that of the new Kafka instance, and consume data from the new Kafka instance.
   

   Original consumer clients must continue running. Messages are consumed from both the original and new Kafka instances.

2. Change the Kafka connection address of the producer to that of the new Kafka instance.
3. Restart the producer client to migrate the production service to the new Kafka instance.
4. After the production service is migrated, check whether the consumption service connected to the new Kafka instance is normal.
5. After all data in the original Kafka is consumed, close the original consumption clients.
6. The migration is complete.

In this scheme, the migration process is controlled by services. For a certain period of time, the consumption service consumes messages from both the original and new Kafka instances. Before the migration, message consumption from the new Kafka instance has already started, so there is no latency. However, early on in the migration, data is consumed from both the original and new Kafka instances, so the messages may not be consumed in the order that they are produced. This scheme is suitable for services that require low latency but do not require strict message sequence.

How Do I Migrate Persisted Data Along with Services?

You can migrate consumed data from the original instance to a new instance by using the open-source tool MirrorMaker. This tool mirrors the original Kafka producer and consumer into new ones and migrates data to the new Kafka instance.

Note that each cloud Kafka instance stores data in three replicas. Therefore, the storage space of the new instance should be three times that of the original single-replica message storage.