Migrating Data Online

Scenario

If the source and target instances are interconnected and the SYNC and PSYNC commands are supported in the source instance, data can be migrated online in full or incrementally from the source to the target.

Prerequisites

• Before migrating data, read through Introduction to Migration with DCS to learn about the DCS data migration function and select an appropriate target instance.
• To migrate data from a single-node or master/standby instance to a Redis Cluster instance, check if any data exists in DBs other than DB0 in the source instance. If yes, move the data to DB0 by using the open-source tool Rump. Otherwise, the migration will fail because a Redis Cluster instance has only one DB. For details about the migration operations, see Online Migration with Rump.

Obtaining Information About the Source Redis Instance

• If the source is a cloud Redis instance, obtain its name.
• If the source is self-hosted Redis, obtain its IP address or domain name and port number.

Prepare the Target DCS Redis Instance

• If a target DCS Redis instance is not available, create one first. For details, see Creating a DCS Redis Instance.
• If a target instance is available, you do not need to create a new one. However, you must clear the instance data before the migration. For details, see Clearing DCS Instance Data.

Requirements on the Network Between the Online Migration Task, Source Redis, and Target Redis

• If the source or target of online migration is Redis in the cloud, the selected Redis instance must be in the same VPC as the migration task. Otherwise, the migration task may fail to connect to the cloud Redis instance.
• In special scenarios, if you have enabled cross-VPC access between the migration task and the cloud Redis instance, the cloud Redis instance and the migration task can be in different VPCs.

Table 1 lists the requirements on the network between the online migration task, source Redis, and target Redis.

Create a Migration Task

1. Log in to the DCS console.
2. Click in the upper left corner and select a region and a project.
3. In the navigation pane, choose Data Migration. The migration task list is displayed.
4. Click Create Online Migration Task.
5. Enter the task name and description.
6. Select a VPC and security group.
7. Click Next.
8. Click Submit.

Configuring the Online Migration Task

1. On the Online Migration tab page, click Configure in the row containing the online migration task you just created.
2. Specify Migration Type.

   Supported migration types are Full and Full + incremental, which are described in Table 2.

   Table 2 Migration type description

   Migration Type	Description
   Full	Suitable for scenarios where services can be interrupted. Data is migrated at one time. Source instance data updated during the migration will not be migrated to the target instance.
   Full + incremental	Suitable for scenarios requiring minimal service downtime. The incremental migration parses logs to ensure data consistency between the source and target instances. Once incremental migration starts, it remains Migrating until you click Stop in the Operation column. After the migration is stopped, data in the source instance will not be lost, but data will not be written to the target instance. When the transmission network is stable, the delay of incremental migration is within seconds. The actual delay depends on the transmission quality of the network link.

3. Configure source Redis and target Redis.
   1. Source Redis Type: Select Redis in the cloud or Self-hosted Redis as required.
      • Redis in the cloud: a DCS Redis instance that is in the same VPC as the migration task
      • Self-hosted Redis: self-hosted Redis in another cloud, or in on-premises data centers. If you select this option, enter Redis addresses.
   2. If the instance is password-protected, you can click Test Connection to check whether the instance password is correct and whether the network is connected.

4. For Target Instance, select the DCS Redis Instance prepared in Prepare the Target DCS Redis Instance.

   If the instance is password-protected, you can click Test Connection to check whether the instance password meets the requirements.

   

   If the source and target Redis instances are connected but are in different regions of DCS, you can only select Self-hosted Redis for Target Redis Type and enter the instance addresses, regardless of whether the target Redis instance is self-hosted or in the cloud.

5. Click Next.
6. Confirm the migration task details and click Submit.

   Go back to the data migration task list. After the migration is successful, the task status changes to Successful.

   

   If the migration type is full+incremental, the migration task status will remain Migrating until you click Stop.