Data Transmission Service:Synchronize data from a self-managed Redis database hosted on an ECS instance to an ApsaraDB for Redis instance

Prerequisites

• The version of the source Redis database is 2.8, 3.0, 3.2, 4.0, 5.0, or 6.0.
  Note

  The version of the destination instance must be the same as or later than that of the source instance. If you want to synchronize data between different versions of instances, make sure that the versions of the source and destination instances are compatible. For example, you can create a pay-as-you-go destination instance to check the compatibility between the source and destination instances. Then, you can release this instance or change the billing method of the instance to subscription.

• The available storage space of the destination ApsaraDB for Redis instance is larger than the total size of the data in the source Redis database.
• In scenarios where the source Redis database is deployed in a cluster architecture: All nodes of the Redis cluster support the PSYNC command and share the same password.

• The timeout period for data replication between the master and replica nodes in the source instance is specified by the repl-timeout parameter. By default, this parameter is set to 60 seconds. We recommend that you run the config set repl-timeout 600 command to set this parameter to 600 seconds. If the source instance stores a large amount of data, you can increase the value of the repl-timeout parameter based on your business requirements.

Usage notes

• DTS uses the resources of the source and destination instances during initial full data synchronization. This may increase the loads on the database servers. If you synchronize a large volume of data or if the server specifications cannot meet your requirements, database services may become unavailable. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination instances. We recommend that you synchronize data during off-peak hours.

• 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 the bind parameter is configured in the redis.conf file of the source Redis database, you must set the value of this parameter to the internal IP address of the ECS instance. The setting ensures that DTS can connect to the source database.
• To ensure the stability of data synchronization, we recommend that you increase the value of the repl-backlog-size parameter in the redis.conf file of the source Redis database.
• To ensure the synchronization quality, DTS adds the following key to the source Redis database: DTS_REDIS_TIMESTAMP_HEARTBEAT. This key is used to record the time when data is synchronized to ApsaraDB for Redis.
• We recommend that you do not run the FLUSHDB or FLUSHALL command in the source database during data synchronization between Redis clusters. If you run one of the commands in the source database during data synchronization between Redis clusters, data inconsistency may occur between the source Redis database and destination ApsaraDB for Redis instance.

• 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?

• During data synchronization, 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 synchronization task. To ensure data consistency, we recommend that you clear the data that has been synchronized to the destination instance before you reconfigure the data synchronization task.
• During data synchronization, if the endpoint of the self-managed Redis database is changed, you must reconfigure the data synchronization task.

• Limits on synchronizing 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 synchronization. This prevents the data synchronization 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 synchronization quality, Data Transmission Service (DTS) adds a key prefixed with DTS_REDIS_TIMESTAMP_HEARTBEAT to the source database. This key is used to record the time when data is synchronized to the destination database. If the source database is deployed in a cluster architecture, DTS adds this key to each shard. The key is filtered out during data synchronization. After the data synchronization 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 synchronization task does not have the permissions to run the SETEX command, the reported latency may be inaccurate.

• If the transparent data encryption (TDE) feature is enabled for the destination instance, you cannot use DTS to synchronize data.

Billing

Supported synchronization topologies

• One-way one-to-one synchronization

• One-way one-to-many synchronization

• One-way cascade synchronization

For more information, see Synchronization topologies.

Operations that can be synchronized

• APPEND

• BITOP, BLPOP, BRPOP, and BRPOPLPUSH

• DECR, DECRBY, and DEL

• EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT

• 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, and PSETEX

• 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

• SWAPDB and UNLINK (supported only if the engine version of the source instance is 4.0)

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

Procedure

1. Go to the Data Synchronization 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 Synchronization.

   Note

   • Operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.

   • You can also go to the Data Synchronization Tasks page of the new DTS console.

2. On the right side of Data Synchronization Tasks, select the region in which the data synchronization instance resides.

   Note

   If you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.

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 assigns a name to the task. 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	Database Type	The type of the source database. Select ApsaraDB for Redis Enhanced Edition (Tair).
   	Access Method	The access method of the source database. Select Self-managed Database on ECS.
   	Instance Region	The region in which the source Redis database resides.
   	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, No is selected.
   	ECS Instance ID	The ID of the 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 in which the source Redis database is deployed. 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 for the source Redis database. Specify the database password in the <user>:<password> format. For example, if the username of the account that you use to log on to the source Redis database is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
   Destination Database	Database Type	The type of the destination database. Select ApsaraDB for Redis Enhanced Edition (Tair).
   	Access Method	The access method of the destination database. 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 database password of the destination ApsaraDB for Redis instance. Note Specify the database password in the <user>:<password> format. For example, if the username of the account that you use to log on to the destination ApsaraDB for Redis instance is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.

4. In the lower part of the page, click Test Connectivity and Proceed.

   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, and you must ensure that the ECS instance can access the database. 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. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

   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 synchronize 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.

5. Configure objects to synchronize and advanced settings.
   

   Parameter	Description
   Synchronization Type	The type of the synchronization task. By default, Full Data Synchronization + Incremental Data Synchronization is selected.
   Processing Mode of Conflicting Tables
   Use Slave Node	If the Instance Mode parameter of the source Redis database is set to Cluster, you can pull data from the master or replica nodes.
   Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select only databases as objects to be synchronized. Keys cannot be selected as objects to be synchronized.
   Selected Objects	The objects to be synchronized. In this scenario, you cannot rename the objects.

6. Click Next: Advanced Settings to configure advanced settings.
   
   • Data Verification Settings

     For more information about how to enable data verification, see Enable data verification.

   • Advanced Settings

     Parameter	Description
     Set Alerts	Specifies whether to configure alerting for the data synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert contacts. For more information, see Configure monitoring and alerting for a new DTS task.
     Specify the retry time range for failed connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note If you set different retry time ranges for multiple DTS tasks that have the same source or destination database, the shortest retry time range that is set 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 your earliest opportunity after the source and destination instances are released.
     The wait time before a retry when other issues occur in the source and destination databases.	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set the parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Important The value of the The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connection parameter.
     Enable Throttling for Incremental Data Migration	The load on the destination instance may increase when DTS synchronizes incremental data to the destination instance. You can configure throttling thresholds for the number of rows and the amount of data that can be synchronized per second during incremental data synchronization based on your business requirements. This helps reduce the load on the destination instance.
     Extend Expiration Time of Destination Database Key	The extended time period for keys synchronized from the source database to the destination instance to remain valid. Unit: seconds. If specific commands are run, we recommend that you set the parameter to 600 to ensure data consistency. The specific commands include but are not limited to the following commands: expire key seconds pexpire key milliseconds expireat key timestamp pexpireat key timestampMs
     Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.

7. Click Next: Save Task Settings and Precheck in the lower part of the page.

   You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.

   Note

   • Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.

   • If the task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the causes, run a precheck again.

   • If an alert is triggered for an item during the precheck:

     • If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.

     • If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

8. Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

9. On the Purchase Instance page, configure the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.

   Section	Parameter	Description
   New Instance Class	Billing Method	Subscription: You pay for the instance when you create an instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is charged on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go instance, you can release the pay-as-you-go instance to reduce costs.
   	Resource Group	The resource group on which the instance is run. Default value: default resource group. For more information, see What is Resource Management?.
   	Instance Class	DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business scenario. For more information, see Specifications of data synchronization instances.
   	Subscription Duration	If you select the subscription billing method, set the subscription duration and the number of instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

10. Read and select the check box to agree to the Data Transmission Service (Pay-as-you-go) Service Terms.

11. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.

What to do next

You can run the info keyspace command on the source and destination databases to check whether the numbers of keys of the synchronized objects are the same in the source and destination databases. If you configured a data verification task, you can also view the data verification results. For more information, see View data verification details.