This topic describes how to configure one-way data synchronization between ApsaraDB for MongoDB instances (sharded cluster architecture) by using Data Transmission Service (DTS).

Prerequisites

  • The source and destination ApsaraDB for MongoDB instances are created. For more information, see Create a sharded cluster instance.
    Note For more information about the supported versions, see Overview of data synchronization scenarios.
  • The available storage space of the destination ApsaraDB for MongoDB instance is larger than the total size of the data in the source ApsaraDB for MongoDB instance.
  • The source and destination ApsaraDB for MongoDB instances are deployed in a sharded cluster architecture. You have created databases and collections to be sharded in the source and destination ApsaraDB for MongoDB instances and configured sharding based on your business needs. For more information, see Configure sharding to maximize the performance of shards.
    Note
    • Configuring sharding prevents data from being synchronized to the same shard (a component that stores database data), and gives full play to cluster performance.
    • The shard nodes in a sharded cluster instance share the same account password and endpoint. You have obtained the account password and endpoint. For more information, see Apply for an endpoint for a shard or Configserver node.
    • In this topic, you configure a DTS task and then purchase a DTS instance. You do not need to specify the number of shards in the source ApsaraDB for MongoDB instance (sharded cluster architecture).

      If you purchase a DTS instance before you configure a DTS task, you must specify the number of shards when you purchase the instance.

Precautions

Billing

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

Supported one-way synchronization architecture

DTS supports one-way data synchronization only between two ApsaraDB for MongoDB instances (sharded cluster architecture). DTS does not support one-way data synchronization between multiple ApsaraDB for MongoDB instances.

Synchronization types

Synchronization type Description
Schema synchronization DTS synchronizes the schemas of the required objects from the source ApsaraDB for MongoDB instance to the destination ApsaraDB for MongoDB instance.
Full data synchronization DTS synchronizes all historical data of the required objects from the source ApsaraDB for MongoDB instance to the destination ApsaraDB for MongoDB instance.
Note DTS supports full data synchronization for the following types of objects: database, collection, and index.
Incremental data synchronization DTS synchronizes incremental data from the source ApsaraDB for MongoDB instance to the destination ApsaraDB for MongoDB instance.
Note DTS supports the following types of incremental updates:
  • CREATE COLLECTION and CREATE INDEX
  • DROP COLLECTION and DROP INDEX
  • RENAME COLLECTION

Preparations

Delete the orphaned documents that are generated due to chunk migration failures from the self-managed MongoDB database.

Note If you do not delete the orphaned documents, the migration performance will be compromised. In addition, some documents may have duplicate _id values and unwanted data may be migrated.
  1. Download the cleanupOrphaned.js file.
    wget "http://docs-aliyun.cn-hangzhou.oss.aliyun-inc.com/assets/attach/120562/cn_zh/1564451237979/cleanupOrphaned.js"
  2. Replace test in the cleanupOrphaned.js file with the name of the database from which you want to delete orphaned documents.
    Note If you want to delete orphaned documents from multiple databases, repeat Steps ii and iii.
  3. Run the following command on a shard to delete the orphaned documents from all collections in the specified database:
    Note You must repeat this step on each shard.
    mongo --host <Shardhost> --port <Primaryport>  --authenticationDatabase <database> -u <username> -p <password> cleanupOrphaned.js
    Note
    • <Shardhost>: the IP address of the shard.
    • <Primaryport>: the service port of the primary node in the shard.
    • <database>: the name of the authentication database. The database account is created in this database.
    • <username>: the account that is used to log on to the self-managed MongoDB database.
    • <password>: the password that is used to log on to the self-managed MongoDB database.

    Example:

    In this example, a self-managed MongoDB database has three shards, and you must delete the orphaned documents on each shard.

    mongo --host 172.16.1.10 --port 27018  --authenticationDatabase admin -u root -p 'Test123456' cleanupOrphaned.js
    mongo --host 172.16.1.11 --port 27021 --authenticationDatabase admin -u root -p 'Test123456' cleanupOrphaned.js
    mongo --host 172.16.1.12 --port 27024  --authenticationDatabase admin -u root -p 'Test123456' cleanupOrphaned.js

Procedure

Notice In this topic, you configure a DTS task and then purchase a DTS instance. You do not need to specify the number of shards in the source ApsaraDB for MongoDB instance (sharded cluster architecture).

If you purchase a DTS instance before you configure a DTS task, you must specify the number of shards when you purchase the instance.

  1. Go to the Data Synchronization Tasks page.
    1. Log on to the DMS console.
    2. In the top navigation bar, click DTS.
    3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
  2. On the right side of Data Synchronization Tasks, select the region where the data synchronization instance resides.
    Note If you use the new DTS console, you must select the region where 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.
    Category 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 use a unique task name.

    Source Database Database Type Select MongoDB.
    Access Method Select Cloud Instance.
    Instance Region Select the region where the source ApsaraDB for MongoDB instance resides.
    Architecture Select Sharded Cluster.
    Instance ID Select the ID of the source ApsaraDB for MongoDB instance.
    The name of the authentication database The name of the authentication database to which the objects to be synchronized in the source ApsaraDB for MongoDB instance belong.
    Database Account The database account of the source ApsaraDB for MongoDB instance. The account must have the read permissions on the source, admin, and local databases.
    Database Password

    The password of the database account.

    Shard Account The shard account of the source ApsaraDB for MongoDB instance. For more information, see Apply for an endpoint for a shard or Configserver node.
    Shard Password The shard password of the source ApsaraDB for MongoDB instance.
    Destination Database Database Type Select MongoDB.
    Access Method Select Cloud Instance.
    Instance Region Select the region where the destination ApsaraDB for MongoDB instance resides.
    Architecture Select Sharded Cluster.
    Instance ID Select the ID of the destination ApsaraDB for MongoDB instance.
    The name of the authentication database The name of the authentication database to which the synchronized objects in the destination ApsaraDB for MongoDB instance belong.
    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.
    Database Password

    The password of the database account.

    Shard Account The shard account of the destination ApsaraDB for MongoDB instance.
    Shard Password The shard password of the destination ApsaraDB for MongoDB instance.
  4. In the lower part of the page, click Test Connectivity and Proceed.
    Note
    • You do not need to modify the security settings for ApsaraDB instances (such as ApsaraDB RDS for MySQL and ApsaraDB for MongoDB) and ECS-hosted databases. DTS automatically adds the CIDR blocks of DTS servers to the whitelists of ApsaraDB instances or the security group rules of ECS instances. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
    • After data synchronization is complete, we recommend that you remove the CIDR blocks of DTS servers from the whitelists or security groups.
  5. Select the objects to migrate.
    • Basic Settings
      Parameter Description
      Task Stages

      Incremental Data Synchronization is selected by default. You must 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 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 tables that have the same names as tables in the source database. If the source and destination databases do not contain 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 migrated 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 schema, and a data record has the same primary key 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, initial data synchronization may fail. In this case, only part of the columns are synchronized, or the data synchronization task fails.
      Synchronization Topology Select One-way Synchronization.
      Capitalization of Object Names in Destination Instance

      Specifies 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 make sure that the capitalization of object names is consistent with that of 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 Rightwards arrow icon to add the objects to the Selected Objects section.

      Note You can select databases or collections as the objects to synchronize.
      Selected Objects
      • To rename an object in 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 in the destination instance, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time.
    • Advanced Settings
      Parameter Description
      Set Alerts
      Specifies whether to set alerts for the data synchronization task. If you select yes, DTS sends notifications to contacts if the task fails or the synchronization latency exceeds the upper limit.
      • No: does not set alerts.
      • Yes: sets alerts. In this case, you must also set the alert threshold and alert contacts.
      Retry Time for Failed Connection
      Specifies the retry time range for failed connections. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the retry time range to more than 30 minutes. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails.
      Note
      • If an instance serves as the source or destination database of multiple data synchronization tasks, the less value that is specified for the instance 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 needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
      Configure ETL
      Specify whether you want to enable the ETL feature. For more information, see What is ETL?.
      • If you select Yes, the ETL feature is enabled. You must specify a policy in the text box.
      • If you select No, the ETL feature is disabled.
  6. 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 task fails to pass the precheck, you can click the Info icon icon next to each failed item to view details.
      • After you troubleshoot the issues based on the causes, you can run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the billing method and specifications for the data synchronization instance. The following table describes related parameters.
    Section Parameter Description
    Parameters Billing method
    • Subscription: You pay for your subscription 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 billed on an hourly basis. For short-term use, we recommend that you select the pay-as-you-go billing method. If you no longer need a pay-as-you-go instance, you can release the instance to reduce costs.
    Instance Class DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class 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 or one to three years.
    Note This parameter is available only if you select the subscription billing method.
  9. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  10. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.