This topic describes how to migrate data from a self-managed Redis database to an ApsaraDB for Redis instance by using Data Transmission Service (DTS). DTS supports full data migration and incremental data migration. When you migrate data from a self-managed Redis database to Alibaba Cloud, you can select the two migration types to ensure service continuity.

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 uses the resources of the source and destination databases during full data migration. This may increase the loads on 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.
  • If the data eviction policy (maxmemory-policy) of the destination database is not set to noeviction, data inconsistency may occur between the source and destination databases. 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 expired. 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 an expiration policy 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 on 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. Therefore, the destination database may contain duplicate data records.
  • During data migration, if the number of shards in the self-managed Redis database is increased or decreased, or if you change the database specifications, such as scaling up the memory capacity, you must reconfigure the data migration 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. This prevents the data in the source database from overwriting the data in the destination instance after the task is resumed.
  • Limits on migrating data from a standalone ApsaraDB for Redis instance to an ApsaraDB for Redis cluster instance: Each command can be run only on a single slot in an ApsaraDB for Redis cluster instance. If you perform operations on multiple keys in the source database and the keys belong to different slots, an 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 an ApsaraDB for Redis cluster instance, DTS inserts the key into each shard of the cluster. The key is filtered out during data migration. After the migration task is complete, the key expires.
  • If the source database is a read-only instance or the DTS account does not have the permission to run the SETEX command, the reported latency may be inaccurate.

Billing

Migration typeTask configuration feeInternet traffic fee
Schema migration and full data migrationFree of charge. Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migrationCharged. For more information, see Billing overview.

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

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.

Note If you perform only full data migration, skip the following steps.
  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 old 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 ApsaraDB RDS for MySQL instance resides.
  4. In the upper-right corner of the page, click Create Migration Task.
  5. Configure the source and destination databases. Configure the source and destination databases
    SectionParameterDescription
    N/ATask NameThe 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 DatabaseInstance TypeThe 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 RegionThe region in which the source database resides. If you select User-Created Database with Public IP Address as the instance type, you do not need to specify 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 TypeThe type of the source database. Select Redis.
    Instance ModeThe value of this parameter is set to Standalone and cannot be changed to Cluster.
    Hostname or IP AddressThe address that is used to connect to the self-managed Redis database. In this example, a public IP address is used.
    Port NumberThe 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 PasswordThe password used to connect to the self-managed Redis database.
    Note After you specify the information about the self-managed Oracle 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 DatabaseInstance TypeThe type of the destination database. Select Redis Instance.
    Instance RegionThe region in which the destination ApsaraDB for Redis instance resides.
    Redis Instance IDThe ID of the destination ApsaraDB for Redis instance.
    Database PasswordThe database password used to connect to the destination ApsaraDB for Redis instance.
    Note After you specify the information about the destination 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.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Warning
    • If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, or is a self-managed database hosted on Elastic Compute Service (ECS), DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance or ECS security group rules. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database on data centers or is from other cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database instance or 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 account 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.
    • After the DTS task is completed or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database instance or ECS security group rules.
  7. Select the migration types and the objects to be migrated. Select the migration types and the objects to be migrated
    ParameterDescription
    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 Rightwards arrow 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 objectsThe 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 databasesBy default, if DTS fails to connect to the source and destination databases, DTS retries within the following 12 hours. You can specify the retry time range based on your business requirements. If DTS reconnects 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 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 databases 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 Note icon next to each failed check item to view the related details. Fix the issues as instructed and run the precheck again.
  9. After the task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, set the Channel Specification parameter and select the check box to agree to 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 ApsaraDB RDS for MySQL 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. The data migration task is not delayed
  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.