From MongoDB to DDS

Supported Source and Destination Databases

Prerequisites

• You have logged in to the DRS console.
• Your account balance is greater than or equal to $0 USD.
• For details about the DB types and versions supported by real-time migration, see Supported Databases.
• If a subaccount is used to create a DRS task, ensure that an agency has been added. To create an agency, see Agency Management.

Suggestions

• The success of database migration depends on environment and manual operations. To ensure a smooth migration, perform a migration trial before you start the migration to help you detect and resolve problems in advance.
• In the migration, ensure that no data is written to the destination database to ensure data consistency before and after the migration.
• Start your migration task during off-peak hours. A less active database is easier to migrate successfully. If the data is fairly static, there is less likely to be any severe performance impacts during the migration.
  • If network bandwidth is not limited, the query rate of the source database increases by about 20 MB/s during full migration, and two to four CPUs are occupied.
  • If DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
  • For more information about the impact of DRS on databases, see What Is the Impact of DRS on Source and Destination Databases?
• Data-Level Comparison

  To obtain accurate comparison results, start data comparison at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, data inconsistency may occur, reducing the reliability and validity of the comparison results.

Precautions

Before creating a migration task, read the following notes:

Procedure

This section uses MongoDB sharded clusters as an example to describe how to configure a task for migrating MongoDB databases to DDS Community Edition over a public network.

1. On the Online Migration Management page, click Create Migration Task.
2. On the Create Replication Instance page, select a region, specify the task name, description, and the replication instance details, and click Next.
   Figure 1 Migration task information
   

   Table 3 Task information

   Parameter	Description
   Region	The region where the replication instance is deployed. You can change the region. To reduce latency and improve access speed, select the region closest to your services.
   Task Name	The task name consists of 4 to 50 characters, starts with a letter, and can contain only letters (case-insensitive), digits, hyphens (-), and underscores (_).
   Description	The description can contain up to 256 characters and cannot contain special characters !=<>&'\"

   Figure 2 Replication instance information
   

   Table 4 Replication instance settings

   Parameter	Description
   Data Flow	Select To the cloud. The destination database must be a database on the current cloud.
   Source DB Engine	Select MongoDB.
   Destination DB Engine	Select DDS.
   Network Type	Available options: VPC, VPN or Direct Connect, and Public network. By default, the value is Public network. VPC is suitable for migrations of cloud databases. Public network is suitable for migrations from on-premises or external cloud databases to the destination databases bound with an EIP. VPN is suitable for migrations from on-premises databases to cloud databases or between cloud databases across regions. Direct Connect is suitable for migrations from on-premises databases to cloud databases or between cloud databases across regions.
   Destination DB Instance	Select the DB instance you have created.
   Replication Instance Subnet	The subnet where the replication instance resides. You can also click View Subnet to go to the network console to view the subnet where the instance resides. By default, the DRS instance and the destination DB instance are in the same subnet. You need to select the subnet where the DRS instance resides, and there are available IP addresses for the subnet. To ensure that the replication instance is successfully created, only subnets with DHCP enabled are displayed.
   Migration Type	Full: This migration type is suitable for scenarios where service interruption is permitted. It migrates all objects and data in non-system databases to the destination database at one time. The objects include collections, views, and indexes. NOTE: If you are performing a full migration, do not perform operations on the source database. Otherwise, data generated in the source database during the migration will not be synchronized to the destination database. Full+Incremental: This migration type allows you to migrate data without interrupting services. After a full migration initializes the destination database, an incremental migration initiates and parses logs to ensure data consistency between the source and destination databases. NOTE: If you select Full+Incremental, data generated during the full migration will be continuously synchronized to the destination database, and the source remains accessible.
   Source DB Instance Type	If you select Full+Incremental for Migration Type, set this parameter based on the source database. If the source database is a cluster instance, set this parameter to Cluster. If the source database is a replica set or a single node instance, set this parameter to Non-cluster.
   Obtain Incremental Data	This parameter is available for configuration if Source DB Instance Type is set to Cluster. You can determine how to capture data changes during the incremental synchronization. oplog: For MongoDB 3.2 or later, DRS directly connects to each shard of the source DB instance to extract data. If you select this method, you must disable the balancer of the source database. For details, see How Do I Disable the Balancer? When testing the connectivity between the source and the DRS instance, you need to enter the connection information of each shard in the source database on the task configuration page. changeStream: This method is recommended. For MongoDB 4.0 and later, DRS connects to mongos nodes of the source database to extract data. If you select this method, you must enable the WiredTiger storage engine of the source database. NOTE: Currently, only whitelisted users can use this function.
   Source Shard Quantity	If Source DB Instance Type is set to Cluster and Obtain Incremental Data is set to oplog, you need to enter the number of source database shards. The number of source shards ranges from 2 to 32. Specify this parameter based on the actual number of shards in the source DB.
   Enterprise Project	If the DB instance has been associated with an enterprise project, select the target project from the Enterprise Project drop-down list. You can also go to the ProjectMan console to create a project. For details about how to create a project, see the ProjectMan User Guide.
   Tags	This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 10 tags. After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

3. On the Configure Source and Destination Databases page, wait until the replication instance is created. Then, specify source and destination database information and click Test Connection for both the source and destination databases to check whether they have been connected to the replication instance. After the connection tests are successful, select the check box before the agreement and click Next.
   • Source database information
     Figure 3 Source database information
     

     Table 5 Source database information

     Parameter	Description
     mongos Address	IP address or domain name of the source database in the IP address/Domain name:Port format. The port of the source database. Range: 1 - 65534 You can enter a maximum of three groups of IP addresses or domain names of the source database. Separate multiple values with commas (,). For example: 192.168.0.1:8080,192.168.0.2:8080. Ensure that the entered IP addresses or domain names belong to the same sharded cluster. NOTE: If multiple IP addresses or domain names are entered, the test connection is successful as long as one IP address or domain name is accessible. Therefore, you must ensure that the IP address or domain name is correct.
     Authentication Database	The name of the authentication database. For example: The default authentication database of DDS instance is admin.
     mongos Username	The username for accessing the source database.
     mongos Password	The password for the database username.
     SSL Connection	SSL encrypts the connections between the source and destination databases. If SSL is enabled, upload the SSL CA root certificate. NOTE: The maximum size of a single certificate file that can be uploaded is 500 KB. If the SSL certificate is not used, your data may be at risk.
     Sharded Database	Enter the information about the sharded databases in the source database. If the source is a DDS instance, apply for an IP address for the shard node by referring to Document Database Service User Guide.

     

     The IP address, domain name, username, and password of the source database are encrypted and stored in DRS, and will be cleared after the task is deleted.

   • Destination database configuration
     Figure 4 Destination database information
     

     Table 6 Destination database settings

     Parameter	Description
     DB Instance Name	The DB instance you selected when creating the migration task. This parameter cannot be changed.
     Database Username	The username for accessing the destination database.
     Database Password	The password for the database username.

     

     The username and password of the destination database are encrypted and stored in the database and the replication instance during the migration. After the task is deleted, the username and password are permanently deleted.

4. On the Set Task page, select migration objects and click Next.
   Figure 5 Migration object
   

   Table 7 Migrate Object

   Parameter	Description
   Migrate Account	Accounts to be migrated can be classified into the following types: accounts that can be migrated and accounts that cannot be migrated. You can choose whether to migrate the accounts. Accounts that cannot be migrated or accounts that are not selected will not exist in the destination database. Ensure that your services will not be affected by these accounts. Yes If you need to migrate accounts, see Migrating Accounts. No During the migration, accounts and roles are not migrated.
   Migrate Object	You can choose to migrate all objects, tables, or databases based on your service requirements. All: All objects in the source database are migrated to the destination database. After the migration, the object names will remain the same as those in the source database and cannot be modified. Tables: The selected table-level objects will be migrated. Databases: The selected database-level objects will be migrated. If the source database is changed, click in the upper right corner before selecting migration objects to ensure that the objects to be selected are from the changed source database. NOTE: If you choose not to migrate all of the databases, the migration may fail because the objects, such as stored procedures and views, in the databases to be migrated may have dependencies on other objects that are not migrated. To prevent migration failure, migrate all of the databases. When you select an object, the spaces before and after the object name are not displayed. If there are two or more consecutive spaces in the middle of the object name, only one space is displayed. The search function can help you quickly select the required database objects.

5. On the Check Task page, check the migration task.
   • If any check fails, review the cause and rectify the fault. After the fault is rectified, click Check Again.

     For details about how to handle check failures, see Checking Whether the Source Database Is Connected in Data Replication Service User Guide.

     Figure 6 Pre-check
     
   • If the check is complete and the check success rate is 100%, click Next.
     

     You can proceed to the next step only when all checks are successful. If there are any items that require confirmation, view and confirm the details first before proceeding to the next step.

6. On the displayed page, specify Start Time, Send Notification, SMN Topic, Synchronization Delay Threshold, and Stop Abnormal Tasks After and confirm that the configured information is correct and click Submit to submit the task.
   Figure 7 Task startup settings
   

   Table 8 Task startup settings

   Parameter	Description
   Started Time	Set Start Time to Start upon task creation or Start at a specified time based on site requirements. The Start at a specified time option is recommended. NOTE: The migration task may affect the performance of the source and destination databases. You are advised to start the task in off-peak hours and reserve two to three days for data verification.
   Send Notifications	SMN topic. This parameter is optional. If an exception occurs during migration, the system will send a notification to the specified recipients.
   SMN Topic	This parameter is available only after you enable Send Notifications and create a topic on the SMN console and add a subscriber. For details, see Simple Message Notification User Guide.
   Synchronization Delay Threshold	During an incremental migration, a synchronization delay indicates a time difference (in seconds) of synchronization between the source and destination database. If the synchronization delay exceeds the threshold you specify, DRS will send alarms to the specified recipients. The value ranges from 0 to 3,600. To avoid repeated alarms caused by the fluctuation of delay, an alarm is sent only after the delay has exceeded the threshold for six minutes. NOTE: In the early stages of an incremental migration, there is more delay because more data is waiting to be synchronized. In this situation, no notifications will be sent. Before setting the delay threshold, enable Send Notification. If the delay threshold is set to 0, no notifications will be sent to the recipient.
   Stop Abnormal Tasks After	Number of days after which an abnormal task is automatically stopped. The value must range from 14 to 100. The default value is 14. NOTE: Tasks in the abnormal state are still charged. If tasks remain in the abnormal state for a long time, they cannot be resumed. Abnormal tasks run longer than the period you set (unit: day) will automatically stop to avoid unnecessary fees.

7. After the task is submitted, view and manage it on the Online Migration Management page.
   • You can view the task status. For more information about task status, see Task Statuses.
   • You can click in the upper right corner to view the latest task status.