Data Transmission Service:Migrate data from a self-managed Redis database to an ApsaraDB for Redis instance

Prerequisites

• The engine version of the self-managed Redis database is 2.8, 3.0, 3.2, 4.0, 5.0, or 6.0.

• The self-managed Redis database is deployed in the standalone architecture rather than the cluster architecture.

  Note

  If the self-managed Redis database is deployed in the cluster architecture, you can migrate data by using the data synchronization feature. For more information, see Synchronize data from a self-managed Redis cluster to an ApsaraDB for Redis cluster instance.

• The PSYNC or SYNC command can be run on the self-managed Redis database.

• The available storage space of the destination ApsaraDB for Redis database is larger than the total size of the data in the self-managed Redis database.

Usage notes

• DTS consumes the resources of the source and destination databases during full data migration. This may increase the loads of the database servers. If you migrate a large amount of data or if the server specifications do not meet your requirements, database services may become unavailable. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours.

• By default, the maxmemory-policy parameter that specifies how data is evicted is set to volatile-lru for ApsaraDB for Redis instances. If the destination instance has insufficient memory, data inconsistency may occur between the source and destination instances due to data eviction. In this case, the data synchronization task does not stop running.

  To prevent data inconsistency, we recommend that you set maxmemory-policy to noeviction for the destination instance. This way, the data synchronization task fails if the destination instance has insufficient memory, but data loss can be prevented for the destination instance.

  Note

  For more information about data eviction policies, see How does ApsaraDB for Redis evict data by default?

• If an expiration policy is enabled for specific keys in the source database, these keys may not be deleted at the earliest opportunity after they expire. Therefore, the number of keys in the destination database may be less than that in the source database. You can run the INFO command to view the number of keys in the destination database.

  Note

  The number of keys that do not have the expiration policy enabled or have not expired is the same between the source and destination databases.

• If you run the EVAL or EVALSHA command to call Lua scripts, DTS cannot identify whether these Lua scripts are executed in the destination database. This is because the destination database does not explicitly return the execution results of Lua scripts during incremental data migration.

• When you run the PSYNC or SYNC command to transfer data of the LIST type, DTS does not perform the FLUSH operation on the existing data in the destination database. As a result, the destination database may contain duplicate data records.

• During data migration, if the number of shards in the self-managed Redis database is changed, or if the specifications of the database such as the memory capacity are changed, you must reconfigure the task. To ensure data consistency, we recommend that you clear the data that has been migrated to the destination Redis database before you reconfigure the data migration task.

• During data migration, if the endpoint of the self-managed Redis database is changed, you must reconfigure the data migration task.

• If a data migration task fails and stops, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.

• Limits on migrating data from a standalone Redis instance to a Redis cluster: Each command can be run only on a single slot in a Redis cluster. If you perform operations on multiple keys in the source database and the keys belong to different slots, the following error occurs:

  CROSSSLOT Keys in request don't hash to the same slot

  We recommend that you perform operations on only one key during data migration. This prevents the data migration task from being interrupted.

• If the destination instance is deployed in a cluster architecture and the amount of memory used by a shard in the destination instance reaches the upper limit, or if the available storage space of the destination instance is insufficient, the data synchronization task fails due to out of memory (OOM).

• To ensure the stability of data migration, DTS inserts a key prefixed with DTS_REDIS_TIMESTAMP_HEARTBEAT into the source database to record when data is updated. If the source database is deployed in a cluster architecture, DTS inserts the key into each shard of the cluster. The key is filtered out during data migration. After the data migration task is complete, the key expires.

• If the source database is a read-only database or the source database account that is used to run the data migration task does not have the permissions to run the SETEX command, the reported latency may be inaccurate.

• If Transparent Data Encryption (TDE) is enabled for the destination instance, you cannot use DTS to migrate data.

Billing rules

Migration types

• Full data migration

  DTS migrates existing data of the selected objects from the self-managed Redis database to the destination ApsaraDB for Redis instance.

  Note

  If you perform only full data migration, we recommend that you do not execute DDL statements on the self-managed Redis database during full data migration. This ensures data consistency.

• Incremental data migration

  After full data migration is complete, DTS synchronizes incremental data from the self-managed Redis database to the destination ApsaraDB for Redis instance. Incremental data migration allows you to ensure service continuity when you migrate data from a self-managed Redis database to Alibaba Cloud.

Commands that can be incrementally migrated

• APPEND

• BITOP, BLPOP, BRPOP, and BRPOPLPUSH

• DECR, DECRBY, and DEL

• EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT

• FLUSHALL and FLUSHDB

• GEOADD and GETSET

• HDEL, HINCRBY, HINCRBYFLOAT, HMSET, HSET, and HSETNX

• INCR, INCRBY, and INCRBYFLOAT

• LINSERT, LPOP, LPUSH, LPUSHX, LREM, LSET, and LTRIM

• MOVE, MSET, MSETNX, and MULTI

• PERSIST, PEXPIRE, PEXPIREAT, PFADD, PFMERGE, PSETEX, and PUBLISH

• RENAME, RENAMENX, RESTORE, RPOP, RPOPLPUSH, RPUSH, and RPUSHX

• SADD, SDIFFSTORE, SELECT, SET, SETBIT, SETEX, SETNX, SETRANGE, SINTERSTORE, SMOVE, SPOP, SREM, and SUNIONSTORE

• ZADD, ZINCRBY, ZINTERSTORE, ZREM, ZREMRANGEBYLEX, ZUNIONSTORE, ZREMRANGEBYRANK, and ZREMRANGEBYSCORE

• XADD, XCLAIM, XDEL, XAUTOCLAIM, XGROUP CREATECONSUMER, and XTRIM

Preparations before incremental data migration

To ensure that the incremental data migration task runs as expected, we recommend that you remove the limit on the replication output buffer. In this topic, a server that runs on Linux is used in the example.

1. Use the redis-cli program to connect to the self-managed Redis database.

   Note

   You can use the redis-cli program after you install the Redis client. For more information, visit Redis community official website.

   redis-cli -h <host> -p <port> -a <password>

   Note

   • <host>: the endpoint that is used to connect to the self-managed Redis database. You can use 127.0.0.1 in this example.

   • <port>: the service port number used to connect to the self-managed Redis database. The default port number is 6379.

   • <password>: the password used to connect to the self-managed Redis database.

   Example:

   redis-cli -h 127.0.0.1 -p 6379 -a Test123456

2. Run the following command to remove the limit on the replication output buffer:

   config set client-output-buffer-limit 'slave 0 0 0'

Procedure

1. Log on to the DTS console.

   Note If you are redirected to the Data Management (DMS) console, you can click the icon in the lower-right corner to go to the previous version of the DTS console.

2. In the left-side navigation pane, click Data Migration.

3. In the upper part of the Migration Tasks page, select the region in which the RDS instance resides.

4. In the upper-right corner of the page, click Create Migration Task.

5. Configure the source and destination databases for the data migration task.

   Section	Parameter	Description
   N/A	Task Name	The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
   Source Database	Instance Type	The access method of the source database. In this example, User-Created Database with Public IP Address is selected. Note If you select a different instance type, you must set up the environment that is required for the self-managed database. For more information, see Preparation overview.
   	Instance Region	If you select User-Created Database with Public IP Address for the Instance Type parameter, you do not need to configure the Instance Region parameter. Note If a whitelist is configured for the self-managed Redis database, you must add the CIDR blocks of DTS servers to the whitelist of the database. You can click Get IP Address Segment of DTS next to Instance Region to obtain the CIDR blocks of DTS servers.
   	Database Type	The type of the source database. Select Redis.
   	Instance Mode	The value of this parameter is set to Standalone and cannot be changed to Cluster.
   	Hostname or IP Address	The address that is used to connect to the self-managed Redis database. In this example, a public IP address is used.
   	Port Number	The service port number used to connect to the self-managed Redis database. Default value: 6379. Note The service port of the self-managed Redis database must be accessible over the Internet.
   	Database Password	The password used to connect to the self-managed Redis database. Note After you specify the information about the source database, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information based on the check results.
   Destination Database	Instance Type	The type of the destination database. Select Redis Instance.
   	Instance Region	The region where the destination ApsaraDB for Redis instance resides.
   	Redis Instance ID	The ID of the destination ApsaraDB for Redis instance.
   	Database Password	The database password used to connect to the destination ApsaraDB for Redis instance. Note After you specify the information about the RDS instance, you can click Test Connectivity next to Database Password to check whether the information is valid. If the information is valid, the Passed message appears. If the Failed message appears, click Check next to Failed. Then, modify the information based on the check results.

6. In the lower-right corner of the page, click Set Whitelist and Next.

   Warning If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhance the security of your username and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

7. Select the objects to be migrated and the migration types.

   Parameter	Description
   Select the migration types	To perform only full data migration, select only Full Data Migration. To ensure service continuity during data migration, select Full Data Migration and Incremental Data Migration. Note If Incremental Data Migration is not selected, we recommend that you do not write data to the self-managed Redis database during data migration. This ensures data consistency between the source and destination databases.
   Select the objects to be migrated	Select one or more objects from the Available section and click the icon to add the objects to the Selected section. Note You can select only databases as the objects to be migrated.
   Specify whether to rename objects	The objects to be migrated. In this scenario, you cannot rename the objects.
   Specify the retry time range for failed connections to the source and destination databases	By default, if DTS fails to connect to the source or destination database, DTS retries within the following 12 hours. You can specify the retry time range based on your business requirements. If DTS is reconnected to the source and destination databases within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note Within the retry time range in which DTS attempts to reconnect to the source and destination databases, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at the earliest opportunity after the source and destination instances are released.

8. Click Precheck.
   Note

   • A precheck is performed before the migration task starts. The migration task only starts after the precheck succeeds.
   • If the precheck fails, click the icon next to each failed check item to view the related details. Fix the issues as instructed and run the precheck again.

9. Click Next.

10. In the Confirm Settings dialog box, configure the Channel Specification parameter. Then, read and select Data Transmission Service (Pay-as-you-go) Service Terms.

11. Click Buy and Start to start the data migration task.

    • Full data migration

      Do not manually stop a full data migration task. If you manually stop a full data migration task, the data that is migrated to the RDS instance may be incomplete. You can wait until the data migration task automatically stops.

    • Incremental data migration

      An incremental data migration task does not automatically stop. You must manually stop the task.

      Note

      We recommend that you manually stop an incremental data migration task at an appropriate point in time. For example, you can stop the task during off-peak hours or before you switch your workloads over to the ApsaraDB RDS for MySQL instance.

      1. Wait until Incremental Data Migration and The data migration task is not delayed are displayed in the progress bar of the data migration task. Then, stop writing data to the source database for a few minutes. The latency of incremental data migration may be displayed in the progress bar.

      2. Wait until the status of Incremental Data Migration changes to The data migration task is not delayed again. Then, manually stop the migration task.

12. Switch your workloads to the destination ApsaraDB for Redis instance.

What to do next

The database accounts that are used for data migration have the read and write permissions. To ensure database security, you must change the passwords of the self-managed Redis database and the ApsaraDB for Redis instance after the data migration task is complete.