Synchronize data between ApsaraDB RDS for MySQL instances that belong to different Alibaba Cloud accounts - Data Transmission Service

This topic describes how to synchronize data between ApsaraDB RDS for MySQL instances that belong to different Alibaba Cloud accounts by using Data Transmission Service (DTS).

Prerequisites

The source and destination ApsaraDB RDS for MySQL instances are created. For more information, see Create an ApsaraDB RDS for MySQL instance.
The available storage space of the destination ApsaraDB RDS for MySQL instance is larger than the total size of the data in the source ApsaraDB RDS for MySQL instance.

Usage notes

DTS uses read and write resources of the source and destination databases during initial full data synchronization. This may increase the loads of the database servers. If the database performance or specifications are unfavorable, or the data volume is large, database services may become unavailable. For example, DTS occupies a large amount of read and write resources in the following cases: a large number of slow SQL queries are performed on the source database, the tables have no primary keys, or a deadlock occurs in the destination database. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination databases. We recommend that you synchronize data during off-peak hours. For example, you can synchronize data when the CPU utilization of the source and destination databases is less than 30%.
The tables to be synchronized in the source database must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination instance. After initial full data synchronization is complete, the tablespace of the destination instance is larger than that of the source instance.
Data synchronization across Alibaba Cloud accounts and regions is supported. Two-way synchronization across Alibaba Cloud accounts is supported only between ApsaraDB RDS for MySQL instances.
After the operations described in the "Preparations" section are complete, you can obtain the information about database instances within the Alibaba Cloud accounts to which the source and destination instances belong.
Important
We recommend that you delete the Resource Access Management (RAM) role that you create during preparations at the earliest opportunity after the data synchronization task is complete.
If your destination instance is not an ApsaraDB RDS for MySQL instance, operations across Alibaba Cloud accounts are not supported.

Supported synchronization topologies

One-way one-to-one synchronization
One-way one-to-many synchronization
One-way cascade synchronization
One-way many-to-one synchronization

For more information about the synchronization topologies that are supported by DTS, see Synchronization topologies.

SQL operations that can be synchronized

Operation type	SQL statement
DML	INSERT, UPDATE, DELETE, and REPLACE
DDL	ALTER TABLE and ALTER VIEW CREATE FUNCTION, CREATE INDEX, CREATE PROCEDURE, CREATE TABLE, and CREATE VIEW DROP INDEX and DROP TABLE RENAME TABLE TRUNCATE TABLE

Permissions required for database accounts

Database	Required permission	References
Source ApsaraDB RDS for MySQL instance	Read and write permissions on the objects to be synchronized	Create databases and accounts for an ApsaraDB RDS for MySQL instance and Modify the permissions of a standard account on an ApsaraDB RDS for MySQL instance
Destination ApsaraDB RDS for MySQL instance	Read and write permissions on the destination database

Limits

RENAME TABLE operations may cause data inconsistency between the source and destination databases. For example, if only Table A is selected as the object to be synchronized and is renamed Table B, Table B cannot be synchronized to the destination database. To prevent this situation, you can select the entire database where Table A is located as the object to be synchronized when you configure the data synchronization task.

Billing

Synchronization type	Task configuration fee
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

Preparations

Required. Obtain the IDs of the Alibaba Cloud accounts to which the source and destination instances belong and the Alibaba Cloud account that is used to create the DTS task.
Note
Skip the step if you have obtained the IDs of the required Alibaba Cloud accounts.
1. Log on to the Account Management console by using each of the Alibaba Cloud accounts to which the source and destination instances belong and the Alibaba Cloud account that is used to create the DTS task.
2. Optional. In the left-side navigation pane, click Basic Information.
3. View and record the value of the Account ID parameter.
4. Use each of the Alibaba Cloud accounts to which the source and destination instances belong to perform Steps 2 to 4.
  Note
  For database instances that do not require cross-account synchronization, Steps 2 to 4 are not necessary.

Create a RAM role.

Important

If you grant permissions to a RAM role by using a RAM user, an error message about invalid permissions may appear when you configure a DTS task.

Log on to the RAM console by using the Alibaba Cloud account to which the source or destination instance belongs.
In the left-side navigation pane, choose Identities > Roles.
Important
Do not choose Identities > Users. Otherwise, DTS cannot access the instance, and an error will be reported.
On the Roles page, click Create Role.
In the Create Role panel, select Alibaba Cloud Account for the Select Trusted Entity parameter and click Next.

In the Configure Role step, configure parameters for the RAM role. 信任账号

Parameter	Description
RAM Role Name	The name of the RAM role. In this example, ram-for-dts is used as the name of the RAM role that is created by using the Alibaba Cloud account to which the source or destination instance belongs. Note The role name must be 1 to 64 characters in length and can contain letters, digits, and hyphens (-).
Note	Optional. The description for the RAM role.
Select Trusted Alibaba Cloud Account	Select Other Alibaba Cloud Account and enter the ID of the Alibaba Cloud account that you use to create the DTS task. For more information about how to obtain the ID of an Alibaba Cloud account, see Preparations. Important If the account that creates the synchronization task also owns the destination instance, its ID only needs to be specified by the account to which the source instance belongs. If the account that creates the synchronization task also owns the source instance, its ID only needs to be specified by the account to which the destination instance belongs. If the account that creates the synchronization task does not own the source or destination instance, its ID needs to be specified by both the accounts to which the source and destination instances belong.

Click OK.

Click Input and Attach to grant permissions to the created RAM role.
1. In the Add Permissions panel, select System Policy as Type.
2. In the Policy Name field, enter AliyunDTSRolePolicy.
3. Click OK.
4. After you grant the permissions, click Close.
Modify the trust policy.
1. On the Roles page, find the RAM role that you created and click the role name to view details.
2. On the Basic Information page of the RAM role, click the Trust Policy Management tab.
3. On the Trust Policy Management tab, click Edit Trust Policy.
4. Copy the following code to the code editor:
```
{
    "Statement": [
        {
            "Action": "sts:AssumeRole",
            "Effect": "Allow",
            "Principal": {
                "RAM": [
                    "acs:ram::<ID of the Alibaba Cloud account>:root"
                ],
                "Service": [
                    "<ID of the Alibaba Cloud account>@dts.aliyuncs.com"
                ]
            }
        }
    ],
    "Version": "1"
}
```
5. In the preceding code, replace ID of the Alibaba Cloud account with the Alibaba Cloud account ID that is used to create the DTS task.
6. Click OK.

Procedure

Go to the Data Synchronization Tasks page in the Data Management (DMS) console.
1. Log on to the DMS console by using the Alibaba Cloud account ID that is configured in the trust policy.
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 Configure the DMS console based on your business requirements.
- You can also go to the Data Synchronization Tasks page of the new DTS console.
From the drop-down list to the right 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.

Click Create Task. Configure the source and destination databases.

Warning

After you select the source and destination instances, we recommend that you read the Limits displayed in the upper part of the page. This helps you create and run the data synchronization 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	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 instance. Select MySQL.
	Access Method	The access method of the destination instance. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source ApsaraDB RDS for MySQL instance resides. Note You can select different regions for the source and destination ApsaraDB RDS for MySQL instances.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, Yes is selected.
	Alibaba Cloud Account	The ID of the Alibaba Cloud account to which the source instance belongs. For more information about how to obtain the ID of an Alibaba Cloud account, see Preparations.
	RAM Role Name	The name of the role that you configured by using the Alibaba Cloud account to which the source instance belongs. In this example, the ram-for-dts role that you created in Preparations is used.
	RDS Instance ID	The ID of the source ApsaraDB RDS for MySQL instance. Note If an alert message appears when you select the ID of an ApsaraDB RDS for MySQL instance, modify the parameter values as prompted. For more information, see Troubleshooting.
	Database Account	The database account of the source ApsaraDB RDS for MySQL instance.
	Database Password	The password of the database account.
	Encryption	Specifies whether to encrypt the connection to the destination instance. Select Non-encrypted or SSL-encrypted based on your business requirements. In this example, Non-encrypted is selected. Note If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.
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 instance. Select MySQL.
	Access Method	The access method of the destination instance. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination ApsaraDB RDS for MySQL instance resides. Note You can select different regions for the source and destination ApsaraDB RDS for MySQL instances.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, Yes is selected.
	Alibaba Cloud Account	The ID of the Alibaba Cloud account to which the destination instance belongs. For more information about how to obtain the ID of an Alibaba Cloud account, see Preparations.
	RAM Role Name	The name of the role that you configured by using the Alibaba Cloud account to which the destination instance belongs. In this example, the ram-for-dts role that you created in Preparations is used.
	RDS Instance ID	The ID of the destination ApsaraDB RDS for MySQL instance.
	Database Account	The database account of the destination ApsaraDB RDS for MySQL instance.
	Database Password	The password of the database account.
	Encryption	Specifies whether to encrypt the connection to the destination instance. Select Non-encrypted or SSL-encrypted based on your business requirements. In this example, Non-encrypted is selected. Note If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.

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.

Configure objects to be synchronized and advanced settings.

Parameter	Description
Synchronization Types	By default, Incremental Data Synchronization is selected. We recommend that you also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of selected objects from the source instance to the destination instance. The historical data serves as the basis for subsequent incremental synchronization.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data synchronization task cannot be started. Note You can use the object name mapping feature to rename the tables that are synchronized to the destination database. You can use this feature if the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed. For more information, see Map object names. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur, and your business may be exposed to potential risks. If the source and destination databases have the same schemas, and a data record has the same primary key value as an existing data record in the destination database: During full data synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. During incremental data synchronization, DTS synchronizes the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, data may fail to be initialized, only some columns are synchronized, or the data synchronization task fails. Operate with caution.
Method to Migrate Triggers in Source Database	The method used to synchronize triggers from the source database. You can select a synchronization method based on your business requirements. If no triggers are to be synchronized, you do not need to configure this parameter. For more information, see Synchronize or migrate triggers from the source database.
Enable Migration Assessment	Specifies whether to enable synchronization assessment. You can check whether the schemas of the source and destination databases, such as the length of indexes, stored procedures, and dependent tables, meet the requirements. You can select Yes or No based on your business requirements. If you select Yes, the precheck may take more time. You can view the assessment results during the precheck. The assessment results do not affect the precheck results. Note This parameter is displayed only if Schema Synchronization is selected for the Synchronization Types parameter. If you select Yes, the precheck may take more time. You can view the assessment results during the precheck. The assessment results do not affect the precheck results.Assessment Result
Synchronization Topology	In this example, One-way Synchronization is selected.
Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to ensure that the capitalization of object names is consistent with that in the source or destination database. For more information, see Specify the capitalization of object names in the destination instance.
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 columns, tables, or databases as the objects to be synchronized. If you select tables or columns as the objects to be synchronized, DTS does not synchronize other objects such as views, triggers, or stored procedures to the destination database.
Selected Objects	To rename an object that you want to synchronize to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information about the SQL statements that can be synchronized, see the SQL operations that can be synchronized section of this topic. To specify WHERE conditions to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Use SQL conditions to filter data.

Click Next: Advanced Settings to configure advanced settings.

Data Verification Settings
For more information about how to configure the data verification feature, 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 when you create a DTS task.
Copy the temporary table of the Online DDL tool that is generated in the source table to the destination database.	If you use Data Management (DMS) or the gh-ost tool to perform online DDL operations on the source database, you can specify whether to synchronize the data of temporary tables generated by online DDL operations. Important You cannot use tools such as pt-online-schema-change to perform online DDL operations on the source database. Otherwise, the DTS task fails. Yes: DTS synchronizes the data of temporary tables generated by online DDL operations. Note If online DDL operations generate a large amount of data, the data synchronization task may take an extended period of time to complete. No, Adapt to DMS Online DDL: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL operations that are performed by using Data Management (DMS) are synchronized. Note If you select this option, the tables in the destination database may be locked. No, Adapt to gh-ost: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL operations that are performed by using the gh-ost tool are synchronized. You can use the default or custom regular expressions to filter out the shadow tables of the gh-ost tool and tables that are not required. Note If you select this option, the tables in the destination database may be locked.
Whether to Migrate Accounts	Specifies whether to synchronize the account information of the source database. You can configure this parameter based on your business requirements. If you select Yes, you must select the accounts that you want to synchronize and check the permissions of the source and destination database accounts used in the data synchronization task. Important The account of the source database must have the SELECT permission on the mysql.user, mysql.db, mysql.columns_priv, and mysql.tables_priv metadata tables. The account of the destination database must have the CREATE USER and GRANT OPTION permissions on the destination database. The accounts that already exist in the destination database and the system accounts of the source database, such as root, mysql.infoschema, mysql.session, and mysql.sys, cannot be synchronized.
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 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 Full Data Migration	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data synchronization based on your business requirements. To configure throttling, you need to specify the Query Rate on Source Database, RPS of Full Data Migration, and BPS of Full Data Migration parameters. This reduces the loads of the destination database server. Note This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter.
Enable Throttling for Incremental Data Migration	You can also enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you need to specify the RPS of Incremental Data Migration and BPS of Incremental Data Migration parameters. This reduces the loads of the destination database server.
Configure ETL	Specifies whether to configure 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.
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.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

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.

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 synchronization task. You can view the progress of the task in the task list.

Troubleshooting

The following table describes the common alert messages and the corresponding solutions when you configure the source instance.

Alert message	Solution
	The value of the Alibaba Cloud Account parameter is invalid. Check whether you enter a valid ID of the Alibaba Cloud account to which the source or destination instance belongs. For more information, see Preparations.
	Possible causes: The value of the RAM Role Name parameter is invalid. Check whether you enter a valid RAM role name of the Alibaba Cloud account to which the source or destination instance belongs. The required permissions are not granted to the RAM role. Use the Alibaba Cloud account to which the source or destination instance belongs to grant permissions. Note For more information, see Preparations.
	Possible causes: The value of the RAM Role Name parameter is invalid. Check whether you enter a valid RAM role name of the Alibaba Cloud account to which the source or destination instance belongs. The required permissions are not granted to the RAM role. Check whether you have granted the required permissions to the RAM role. The trust policy of the RAM role is not modified. Check whether you correctly have modified the trust policy for the RAM role. Note For more information, see Preparations.
	The RAM role that you specify in the RAM Role Name parameter is not granted permissions by clicking Input and Attach on the Roles page in the RAM console. Grant the required permissions to the RAM role by clicking Input and Attach on the Roles page and create a task again. For example, you must grant the required permissions to the RAM role of the Alibaba Cloud account to which the source instance belongs. For information about how to grant permissions to a RAM role, see the "Grant permissions to an existing RAM role" section of the Configure RAM authorization for cross-account data migration or synchronization topic.