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

  • A self-managed Redis database and an ApsaraDB for Redis instance are created. For more information about how to create an ApsaraDB for Redis instance, see Step 1: Create an ApsaraDB for Redis instance.
  • The engine version of the self-managed Redis database is 2.8, 3.0, 3.2, 4.0, 5.0, or 6.0.
  • 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.

Precautions

  • 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.
  • If the maxmemory-policy parameter of the destination instance is not set to noeviction, data inconsistency may occur between the source and destination instances. 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. During incremental data migration, the destination database does not explicitly return the execution results of Lua scripts.
  • 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 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 task.
  • During data migration, if the address of the self-managed Redis database changes, you must reconfigure the task.
  • If a data migration task fails, 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 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. Otherwise, the migration task will be interrupted.

Billing

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

Migration types

  • Full data migration
    DTS migrates historical data of the required 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 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.

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. Go to the Data Migration Tasks page.
    1. Log on to the Data Management (DMS) console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
    Note You can also configure the settings by using the new DTS console.
  2. From the drop-down list to the right of Data Migration Tasks, select the region in which your data migration instance resides.
    Note If you use the new DTS console, select the region in which your data migration instance resides in the upper-left corner.
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Section Parameter Description
    N/A Task Name

    The name of the task. DTS automatically generates a task name. We recommend that you specify a descriptive name to identify the task. You do not need to specify a unique task name.

    Source Database Select Instance
    The instance that you want to use. You can choose whether to use an existing instance based on your business requirements.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must set parameters for the database.
    Database Type Select ApsaraDB for Redis Enhanced Edition (Tair).
    Access Method The access method of the source database. In this example, Self-managed Database on ECS is selected.
    Instance Region The region in which the source Redis database resides.
    Replicate Data Across Alibaba Cloud Accounts Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
    ECS Instance ID The ID of the Elastic Compute Service (ECS) instance that hosts the source Redis database.
    Note If the source Redis database is deployed in a cluster architecture, select the ID of the ECS instance on which a master node resides.
    Instance Mode The architecture of the source Redis database. Select Standalone or Cluster.
    Port Number The service port number of the source Redis database. Default value: 6379.
    Note If the source Redis database is deployed in a cluster architecture, enter the service port number of a master node.
    Database Password The password of the source Redis database.
    Note
    • This parameter is optional and can be left empty if no password is set.
    • The database password is in the <user>:<password> format. For example, if the username of the account that you use to log on to the Redis database is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
    Destination Database Select Instance
    The instance that you want to use. You can choose whether to use an existing instance based on your business requirements.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must set parameters for the database.
    Database Type Select ApsaraDB for Redis Enhanced Edition (Tair).
    Access Method Select Alibaba Cloud Instance.
    Instance Region The region in which the destination ApsaraDB for Redis instance resides.
    Instance ID The ID of the destination ApsaraDB for Redis instance.
    Database Password The password of the destination Redis database.
    Note The database password is in the <user>:<password> format. For example, if the username of the account that you use to log on to the Redis database is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
  4. In the lower part of the page for this step, click Test Connectivity and Proceed.
    Warning
    • If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance. 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 that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database 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, Alibaba Cloud 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: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
    • After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist or ECS security group rules.
  5. Select objects for the task and configure advanced settings.
    Parameter Description
    Task Stages

    Select Full Data Migration and Incremental Data Migration.

    Processing Mode of Conflicting Tables
    • Precheck and Report Errors: checks whether the tables in the destination database are empty. If the tables in the destination database do not contain keys, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started.

    • Ignore Errors and Proceed: skips the check items for empty tables in the destination database.
      Warning If you select Ignore Errors and Proceed and the destination database contains the same keys as the source database, the values of the keys in the destination database are overwritten.
    Source Objects

    Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

    Note You can select only databases as the objects to be migrated. Keys cannot be selected as the objects to be migrated.
    Selected Objects The objects to be migrated. In this scenario, you cannot rename the objects.
  6. Click Next: Advanced Settings to configure advanced settings.
    Parameter Description
    Set Alerts
    Specifies whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications. Valid values:
    • No: does not set alerts.
    • Yes: sets alerts. If you select Yes, you must also set the alert threshold and alert contacts.
    Retry Time for Failed Connections
    The retry time range for failed connections. If the data migration task fails, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time range to more than 30 minutes. 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
    • If you set different retry time ranges for multiple data migration tasks that have the same source or destination database, the value that is set later takes precedence.
    • When DTS retries a connection, 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.
    Extend Expiration Time of Destination Database Key
    The extended time period for keys migrated from the source database to the destination instance to remain valid. Unit: seconds. If specific commands are used, such as the following commands, we recommend that you set the parameter to 600 to ensure data consistency.
    expire key seconds
    pexpire key milliseconds
    expireat key timestamp
    pexpireat key timestampMs
    Configure ETL
    Specifies whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values:
  7. In the lower part of the page, click Next: Save Task Settings and Precheck.
    Note
    • Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
    • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details.
      • You can troubleshoot the issues based on the causes and run a precheck again. For more information, see Precheck.
      • If you do not need to troubleshoot the issues, you can ignore the failed items and run a precheck again.
  8. Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.
  9. On the Purchase Instance page, specify the Instance Class parameter for the data migration instance. The following table describes the parameter.
    Section Parameter Description
    New Instance Class Instance Class

    DTS provides several instance classes that have different performance in migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

  10. Read and select the check box for Data Transmission Service (Pay-as-you-go) Service Terms.
  11. Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.