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

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 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.
You can run the PSYNC or SYNC command 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 data migration from a standalone Redis database to a Redis database deployed in the cluster architecture: Each command can be run only on a single slot in a Redis database deployed in the cluster architecture. 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. Otherwise, the migration task is 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 type	Instance configuration fee	Internet traffic fee
Full data migration	Free of charge.	Free of charge in this example.
Full data migration and incremental data migration	Charged. For more information, see Billing overview.	Free of charge in this example.

Migration types

Full data migration
Data Transmission Service (DTS) migrates all existing data of objects from the source self-managed Redis database to the destination ApsaraDB for Redis instance.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source self-managed Redis database to the destination ApsaraDB for Redis instance. Incremental data migration ensures 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.

Note

If you perform only full data migration, skip the following steps.

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
```
Run the following command to remove the limit on the replication output buffer:
```
config set client-output-buffer-limit 'slave 0 0 0'
```

Procedure

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
- 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 Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note
If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. In the Create Task wizard, configure the source and destination databases. The following table describes the parameters.

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	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the 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. 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 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. 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 source Redis database is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
	Encryption	Specifies whether to encrypt the connection to the source database. Select Non-encrypted or SSL-encrypted based on your business requirements. If the SSL encryption feature is disabled for the source self-managed Redis instance, select Non-encrypted. If the SSL encryption feature is enabled for the source self-managed Redis database, select SSL-encrypted. In this case, you must upload a CA Certificate and configure the CA Key parameter.
Destination Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the 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 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 destination ApsaraDB for Redis instance is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.

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.

Configure the objects to be migrated and advanced settings.

Parameter	Description
Migration Types	The migration type. Select a migration type based on your business requirements. Valid values:Migration Types Full Data Migration: runs the SCAN command to traverse the source database and writes the traversed data to the destination database. During the migration, the performance of the source database is affected and data consistency between the source and destination databases is not guaranteed. Full Data Migration + Incremental Data Migration: uses the native synchronization logic of Redis to write data to the destination database by using memory snapshots. This way, the source database is migrated without downtime. Important If the account that the task uses to access the source database does not have the permissions to run the SYNC or PSYNC command on the source database, select Full Data Migration. If you select Full Data Migration, do not write data to the source instance during data migration to ensure data consistency.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database is empty. If the destination database is empty, 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 precheck on whether the destination database is empty. Warning If you select Ignore Errors and Proceed, the data in the source database overwrites the data in the destination database that has the same keys as the source data. This may cause data loss in the destination database. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section. Click the 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 objects to be migrated.
Selected Objects	If you want to select a database to which data is migrated from DB 0 to DB 255 or filter the data to be migrated by prefix, you can use the object name mapping feature or the filtering feature. In the Selected Objects section, right-click the database that you want to migrate. In the Edit Schema dialog box, configure the parameters. For more information, see Map object names and Set filter conditions. Note You cannot map multiple object names at a time.

Click Next: Advanced Settings to configure advanced settings.

Data Verification Settings
For more information about how to configure the data verification feature, see Configure data verification.

Advanced Settings

Parameter	Description
Set Alerts	Specifies whether to configure alerting for the data migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts will receive notifications. Valid values: No: does not configure alerting. Yes: configures alerting. If you select Yes, you must also specify the alert threshold and alert contacts. For more information, see Configure monitoring and alerting.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data migration task is started, 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 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 migration task. Otherwise, the data migration task fails. Note If you set different retry time ranges for multiple data migration tasks that share 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 database and destination instance 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 DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry 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 retry time range, DTS resumes the data migration task. Otherwise, the data migration 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 Connections parameter.
Enable Throttling for Incremental Data Migration	The load on the destination instance may increase when DTS migrates incremental data to the destination instance. You can configure throttling thresholds for the number of rows and the amount of data that can be incrementally migrated per second based on your business requirements. This helps reduce the load on the destination instance.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
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`
Use Slave Node	If the Instance Mode parameter of the source self-managed Redis database is set to Cluster, you can pull data from the master or slave nodes. The default value is No. If you use the default value, data is pulled from the master nodes.
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.

Click Next: Save Task Settings and Precheck in the lower part of the page.
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 View Details next to each failed item. After you troubleshoot the issues based on the causes, run a precheck again. For more information, see the FAQ about prechecks section of the "FAQ" topic.
- If an alert is triggered for an item during the precheck:
  If the alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If the 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.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

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