Configure two-way data synchronization between ApsaraDB for MongoDB replica set instances

Procedure

1. Use one of the following methods to go to the Data Synchronization page and select the region in which the data synchronization instance resides.

   DTS console

   DMS console

   1. Log on to the DTS console.

   2. In the left-side navigation pane, click Data Synchronization.

   3. In the upper-left corner of the page, select the region in which the data synchronization instance resides.

   Note

   The actual 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.

   1. Log on to the DMS console.

   2. In the top navigation bar, move the pointer over Data Development and choose DTS (DTS) > Data Synchronization.

   3. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.

2. Click Create Task to go to the task configuration page.

3. Optional. Click New Configuration Page in the upper-right corner of the page.

   Note

   • Skip this step if the Back to Previous Version button is displayed in the upper-right corner of the page.

   • Specific parameters in the new and previous versions of the configuration page may be different. We recommend that you use the new version of the configuration page.

4. Configure the source and destination databases. The following table describes the parameters.

   Section	Parameter	Description

   Section	Parameter	Description
   N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. 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 Existing Connection	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information. Note In the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections. In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
   	Database Type	The type of the source database. Select MongoDB.
   	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
   	Instance Region	The region where the source ApsaraDB for MongoDB instance resides.
   	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
   	Architecture	The architecture in which the source database is deployed. Select Replica Set.
   	Migration Method	Select Oplog.
   	Instance ID	The ID of the source ApsaraDB for MongoDB instance.
   	Authentication Database	The name of the authentication database that stores the database accounts and passwords of the source ApsaraDB for MongoDB instance. If you did not change the name of the authentication database before, the default value admin is used.
   	Database Account	The database account of the source ApsaraDB for MongoDB instance. The account must have read permissions on the source database, the config database, the admin database, and the local database. Note For more information about how to create a database account and grant permissions to the account, see Use DMS to manage database accounts.
   	Database Password	The password that is used to access the database.
   	Encryption	Specifies whether to encrypt the connection to the source database. You can select Non-encrypted, SSL-encrypted, or Mongo Atlas SSL based on your business requirements. The options available for the Encryption parameter are determined by the values selected for the Access Method and Architecture parameters. The options displayed in the DTS console prevail. Note If the Architecture parameter is set to Sharded Cluster, and the Migration Method parameter is set to Oplog for the ApsaraDB for MongoDB database, the Encryption parameter SSL-encrypted is unavailable. If the source database is a self-managed MongoDB database that uses the Replica Set architecture, the Access Method parameter is not set to Alibaba Cloud Instance, and the Encryption parameter is set to SSL-encrypted, you can upload a certification authority (CA) certificate to verify the connection to the source database.
   Destination Database	Select Existing Connection	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information. Note In the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections. In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
   	Database Type	The type of the destination database. Select MongoDB.
   	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
   	Instance Region	The region where the destination ApsaraDB for MongoDB instance resides.
   	Replicate Data Across Alibaba Cloud Accounts	In this example, a database of the current Alibaba Cloud account is used. Select No.
   	Architecture	The architecture in which the destination database is deployed. Select Replica Set.
   	Instance ID	The ID of the destination ApsaraDB for MongoDB instance.
   	Authentication Database	The name of the authentication database that stores the database accounts and passwords of the destination ApsaraDB for MongoDB instance. If you did not change the name of the authentication database before, the default value admin is used.
   	Database Account	The database account of the destination ApsaraDB for MongoDB instance. The account must have the dbAdminAnyDatabase permission, the read and write permissions on the destination database, and the read permissions on the local database. Note For more information about how to create a database account and grant permissions to the account, see Use DMS to manage database accounts.
   	Database Password	The password that is used to access the database.
   	Encryption	Specifies whether to encrypt the connection to the destination database. You can select Non-encrypted, SSL-encrypted, or Mongo Atlas SSL based on your business requirements. The options available for the Encryption parameter are determined by the values selected for the Access Method and Architecture parameters. The options displayed in the DTS console prevail. Note If the destination database is an ApsaraDB for MongoDB instance and the Architecture parameter is set to Sharded Cluster, the Encryption parameter SSL-encrypted is unavailable. If the destination database is a self-managed MongoDB database that uses the Replica Set architecture, the Access Method parameter is not set to Alibaba Cloud Instance, and the Encryption parameter is set to SSL-encrypted, you can upload a CA certificate to verify the connection to the destination database.

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

   Note

   Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add the CIDR blocks of DTS servers.

6. Configure the objects to be synchronized.

   1. In the Configure Objects step, configure the objects that you want to synchronize.

      Parameter	Description

      Parameter	Description
      Synchronization Types	The synchronization types. By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of the selected objects from the source database to the destination cluster. The historical data is the basis for subsequent incremental synchronization.
      Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains collections that have the same names as the collections in the source database. If the source and destination databases do not contain collections that have identical collection names, the precheck is passed. Otherwise, an error is returned during the precheck, and the data synchronization task cannot be started. Note If the source and destination databases have collections with identical names and the collections in the destination database cannot be deleted or renamed, you can use the object name mapping feature to rename the collections that are synchronized to the destination database. For more information, see Rename an object to be synchronized. Ignore Errors and Proceed: skips the precheck for identical collection 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 a data record in the destination database has the same primary key value or unique key value as a data record in the source database, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained. Data may fail to be initialized, only specific columns are synchronized, or the data synchronization task fails.
      Synchronization Topology	The synchronization topology of the data synchronization task. Select Two-way Synchronization.
      Exclude DDL Operations	Yes: excludes DDL operations. No: synchronizes DDL operations. Important To ensure the stability of two-way data synchronization, you can synchronize DDL operations only in the forward direction.
      Conflict Resolution Policy	The policy that is used to handle conflicts. Set the value to Ignore. This value indicates that the conflict records in the destination database are used if a conflict occurs. If a conflict occurs during data synchronization, the synchronization task ignores the current statement and continues. The conflict records in the destination database are used. For more information, see the Supported conflict detection section of this topic.
      Capitalization of Object Names in Destination Instance	The capitalization of database names and collection 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 the default capitalization of object names 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 databases or collections as the objects to be synchronized.
      Selected Objects	To rename an object to be synchronized in the destination database, right-click the object in the Selected Objects section. For more information, see Map object names. To remove a selected object, click the object in the Selected Objects section and then click the icon to move the object to the Source Objects section. Note To synchronize incremental data by databases or collections, right-click the Selected Objects and select the operations in the dialog box that appears. To filter data in a table to be synchronized, right-click the table in the Selected Objects section. In the dialog box that appears, configure filter conditions. You can specify conditions to filter data during the full data synchronization stage of a data synchronization task. You cannot specify conditions to filter data during the incremental data synchronization stage of a data synchronization task. For more information, see Specify filter conditions. If you use the object name mapping feature to rename the database or collection to which the data is synchronized, other objects that depend on the database or collection may fail to be synchronized.

   2. Click Next: Advanced Settings to configure advanced settings.

      Parameter	Description

      Parameter	Description
      Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
      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 this 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 specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range 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.
      Retry Time for Other Issues	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 this 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 Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections 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 load on the database servers. You can configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters for full data synchronization tasks to reduce the load on the destination database server. Note This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter.
      Only one data type for primary key _id in a single table	Whether the data type for primary key _id in a collection of the data to be synchronized is unique. Valif value: Note This parameter is displayed only if Full Data Synchronization is selected for the Synchronization Types parameter. Yes: The data type is unique. During full data synchronization, DTS does not scan the data type for primary key _id of the data to be synchronized from the source database. No: The data type is not unique. During full data synchronization, DTS scans the data type for primary key _id of the data to be synchronized from the source database.
      Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
      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, you do not need to configure this parameter.
      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.
      Monitoring and Alerting	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 enable alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the "Configure monitoring and alerting when you create a DTS task" section of the Configure monitoring and alerting topic.

   3. Click Next Step: Data Verification to configure data verification.

      For more information about how to use the data verification feature, see Configure a data verification task.

7. Save the task settings and run a precheck.

   • To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.

   • If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.

   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 data synchronization task fails the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, rerun the precheck.

   • 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 issue. 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. Purchase an instance.

   1. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

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

      Section	Parameter	Description

      Section	Parameter	Description
      New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization 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 billed 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 data synchronization instance, you can release the instance to reduce costs.
      	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
      	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
      	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization 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.

   3. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.

   4. Click Buy and Start. In the dialog box that appears, click OK.

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

9. Configure a data synchronization task in the reverse direction.

   1. Wait until the initial synchronization is complete and the Status of the data synchronization task in the forward direction changes to Running.

   2. Find the data synchronization task in the reverse direction and click Configure Task.

   3. Configure the data synchronization task in the reverse direction by repeating Step 3 to Step 7.

      Important

      • When you configure the data synchronization task in the reverse direction, you must select the correct source and destination instances. The source instance in the reverse direction is the destination instance in the forward direction. The destination instance in the reverse direction is the source instance in the forward direction. Make sure that the parameter settings, such as the database name, account, and password, are consistent.

      • We recommend that you do not use the object name mapping feature when you configure the data synchronization task in the reverse direction. Otherwise, data inconsistency may occur.

      • When you configure the source and destination databases of the data synchronization task in the reverse direction, the Instance Region parameter cannot be modified. The number of parameters to configure for a data synchronization task in the reverse direction is less than that for a data synchronization task in the forward direction. Configure the parameters that are displayed in the console.

      • When you configure Processing Mode of Conflicting Tables for a synchronization task in the reverse direction, make sure that the tables that have been synchronized to the destination instance in the forward direction are ignored.

      • You cannot select the objects in the Selected Objects list of the data synchronization task in the forward direction for the data synchronization task in the reverse direction.

      • The data synchronization task in the reverse direction ignores DDL operations.

   4. Wait until Success Rate becomes 100%. Then, click Back.

10. After both the data synchronization task in the forward direction and the data synchronization task in the reverse direction enter the Running, the configuration of two-way data synchronization is complete.