This topic describes how to migrate shards of a user-created MongoDB database to ApsaraDB for MongoDB by using Data Transmission Service (DTS). DTS allows you to migrate historical and incremental data without service disruptions.

For more information about data migration and synchronization solutions, see Overview.

Prerequisites

  • The version of the user-created MongoDB database is 3.0, 3.2, 3.4, 3.6, or 4.0.
  • Each shard in the ApsaraDB for MongoDB instance has sufficient storage space.
    Note For example, a user-created MongoDB database has three shards, and one of these shards occupies the most storage space (500 GB). In this case, the storage space of each shard in the ApsaraDB for MongoDB instance must be greater than 500 GB.

How it works

DTS migrates a user-created MongoDB database by migrating each shard in the database. You must create a data migration task for each shard.

Note The distribution of migrated data in the ApsaraDB for MongoDB instance depends on the shard key that you specify. For more information, see Configure sharding to maximize the performance of shards.
How it works

Precautions

  • During full data migration, DTS occupies some storage space of the source and destination databases. This may increase the load of the database servers. If you migrate a large volume of data or the server specifications cannot meet your requirements, the databases may be overloaded or become unavailable. We recommend that you migrate user-created MongoDB databases during off-peak hours.
  • If the source user-created MongoDB database and the destination ApsaraDB for MongoDB instance run different MongoDB versions or storage engines, ensure that your applications can run on both databases. For more information about MongoDB versions and storage engines that are supported by ApsaraDB for MongoDB, see MongoDB versions and storage engines.

Billing

Migration type Instance configurations Internet traffic
Full data migration Free of charge. Charged only when data is migrated from Alibaba Cloud over the public network. For more information, visit Pricing.
Incremental data migration Charged. For more information, see Pricing.

Migration types

  • Full data migration: All historical data in the source MongoDB database is migrated to the destination MongoDB database.
    Note Data migration is supported at the database, collection, and index levels.
  • Incremental data migration: After full data migration, incremental data is synchronized to the destination MongoDB database.
    Note
    • The create and delete operations for databases, collections, and indexes can also be synchronized.
    • The create, delete, and update operations for documents can be synchronized.

Permissions required for database accounts

Database Full data migration Incremental data migration
Source user-created MongoDB database Read permissions on the source database Read permissions on the source database, admin database, and local database
Destination ApsaraDB for MongoDB instance Read/write permissions on the destination database Read/write permissions on the destination database

For more information about how to create and authorize a database account:

Preparations

  1. Disable the balancer of the user-created MongoDB database. For more information, see Manage the ApsaraDB for MongoDB balancer.
  2. Delete the orphaned documents generated due to migration failures from the user-created MongoDB database.
    Note If the orphaned documents are not deleted, the documents with _id conflicts may exist during migration 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. In the cleanupOrphaned.js file, replace test 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 step ii and step 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 for each shard.
      mongo --host <Shardhost> --port <Primaryport>  --authenticationDatabase <database> -u <username> -p <passowrd> cleanupOrphaned.js
      Note
      • <Shardhost>: the IP address of the shard
      • <Primaryport>: the service port of the primary node of the shard
      • <database>: the name of the authentication database to which the database account belongs
      • <username>: the username that you use to log on to the user-created MongoDB database
      • <password>: the password that you use to log on to the user-created MongoDB database

      Example:

      In this example, a user-created 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
  3. Create required databases and collections in the destination ApsaraDB for MongoDB instance, and configure data sharding for the databases and collections. For more information, see Configure sharding to maximize the performance of shards.
    Note If you configure data sharding before you start data migration, data in the user-created MongoDB database is evenly migrated to the shards in the destination sharded cluster instance. This prevents overloading a single shard.

Procedure

  1. Log on to the DTS console.
  2. In the left-side navigation pane, click Data Migration.
  3. In the Migration Tasks section, select the region in which the ApsaraDB for MongoDB instance resides.Select a region
  4. In the upper-right corner, click Create Migration Task.
  5. Configure the source and destination databases. Configure the source and destination databases
    Section Parameter Description
    N/A Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.
    Source Database Instance Type Select an instance type based on the location where the database is deployed. In this topic, a User-Created Database with Public IP Address is used as an example.
    Note If you select other instance types, you must prepare the environments that are required for the source database. For more information, see Preparation overview.
    Instance Region If Instance Type is set to User-Created Database with Public IP Address, you do not need to specify the Instance Region.
    Note If you have configured a whitelist for the user-created MongoDB database, you must add the CIDR blocks of DTS servers to the whitelist. You can click Get IP Address Segment of DTS next to Instance Region to obtain the CIDR blocks of DTS servers.
    Database Type Select MongoDB.
    Hostname or IP Address Enter the endpoint of a shard for the source database. In this example, enter the public IP address of the shard.
    Note DTS migrates each shard of the source database in turn. In this example, enter the endpoint of the first shard. Then enter the endpoint of the second shard in the second migration task. Repeat this operation until all shards are migrated.
    Port Number Enter the service port of the shard.
    Note The service port of each shard for user-created MongoDB databases must be open to the public network.
    Database Name Enter the name of the authentication database to which the database account belongs.
    Database Account Enter the username of the database account that you use to manage the source database.
    Database Password Enter the password of the source database account.
    Note After you specify the source database information, click Test Connectivity next to Database Password to check whether the information is correct. If the information is correct, the Passed message is displayed. If the Failed message is displayed, click Check in the Failed message to modify the information as prompted.
    Connection Method Select Non-encrypted.
    Note The SSL-encrypted option is available only when you migrate MongoDB Atlas.
    Destination Database Instance Type Select MongoDB Instance.
    Instance Region Select the region in which the ApsaraDB for MongoDB instance resides.
    MongoDB Instance ID Select the ID of the ApsaraDB for MongoDB instance.
    Database Name Enter the name of the authentication database to which the database account belongs.
    Note If you want to use the root account, specify admin for the Database Name parameter.
    Database Account Enter the username of the database account that you use to manage the source database.
    Database Password Enter the password for the destination database account.
    Note After you specify the destination database information, click Test Connectivity next to Database Password to check whether the information is correct. If the information is correct, the Passed message is displayed. If the information is incorrect, the Failed message is displayed, and you must click Check next to the Failed message to modify the information as prompted.
  6. In the lower-right corner of the page, click Set Whitelist and Next.
    Note The CIDR blocks of DTS servers are automatically added to the whitelist of the destination RDS instance. This ensures that DTS servers can connect to the destination ApsaraDB for MongoDB instance. After the migration is completed, you can remove these CIDR blocks from the whitelist. For more information, see Configure a whitelist for a sharded cluster instance.
  7. Select the migration types and objects to be migrated.Select the migration types and objects to be migrated
    Parameter Description
    Migration Types
    • To perform only full data migration, select Full Data Migration.
    • To migrate data with minimal downtime, select both Full Data Migration and Incremental Data Migration.
    Note If the Incremental Data Migration option is not selected, do not write new data to the user-created MongoDB database when full data migration is in progress. Otherwise, data inconsistency may occur.
    Migration objects
    • Select objects from the Available section and click the Right arrow icon to move the objects to the Selected section.
      Note
      • Data in the admin and local databases cannot be migrated.
      • The config database is an internal database. We recommend that you do not migrate data in the config database.
    • A migration object can be a database, collection, or function.
    • By default, the name of an object remains unchanged after migration. You can change the names of the objects in the destination RDS instance by using the object name mapping feature. For more information, see Object name mapping.
  8. In the lower-right corner of the page, click Precheck.
    Note
    • Before you can start the data migration task, a precheck is performed. You can start the data migration task only after the task passes the precheck.
    • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details. Troubleshoot the issues based on the causes and run the precheck again.
  9. After the task passes the precheck, click Next.
  10. In the Confirm Settings dialog box, specify the Channel Specification and select Data Transmission Service (Pay-As-You-Go) Service Terms.
  11. Click Buy and Start to start the migration task.
  12. Repeat step 1 to step 11 to create data migration tasks for the remaining shards.
  13. Stop the data migration task.
    • Full data migration

      Do not manually stop a task during full data migration. Otherwise, data migrated to the destination database will be incomplete. Wait until the data migration task automatically stops.

    • Incremental data migration

      An incremental data migration task does not automatically stop. You must manually stop the migration task.

      Note Select an appropriate time to manually stop the migration task. For example, you can stop the migration task during off-peak hours or before you switch your workloads to the destination instance.
      1. Wait until Incremental Data Migration and The migration task is not delayed appear in the progress bar of the migration task. Then, stop writing data to the source database for a few minutes. The delay time of incremental data migration may be displayed in the progress bar.
      2. After the status of Incremental Data Migration changes to The migration task is not delayed, stop the migration task.Stop a migration task
  14. Switch your workloads to the ApsaraDB for MongoDB instance.