From MongoDB to DDS¶
Supported Source and Destination Databases¶
Source DB | Destination DB |
|---|---|
|
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Supported Migration Objects¶
Different types of migration tasks support different migration objects. For details, see Table 2. DRS will automatically check the objects you selected before the migration.
Type | Precautions |
|---|---|
Migration objects |
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Database Account Permission Requirements¶
To start a migration task, the source and destination database users must have permissions listed in the following table. Different types of migration tasks require different permissions. For details, see Table 3. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.
Type | Full Migration | Full+Incremental Migration |
|---|---|---|
Source database user |
|
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Destination database user | The user who connects to the destination database must have the dbAdminAnyDatabase permission of the admin database and the readWrite permission of the destination database. If the destination database is a cluster instance, the database user must have the clusterManager permission for the admin database. |
Note
For example, the source database user must have the readAnyDatabase permission for the admin database and the read permission for the config database.
db.grantRolesToUser("Username",[{role:"readAnyDatabase",db:"admin"}, {role:"read",db:"config"}])
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.
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¶
The full+incremental migration process consists of four phases: task startup, full synchronization, incremental synchronization, and task completion. A single full migration task contains three phases. To ensure smooth migration, read the following precautions before creating a migration task.
Type | Restrictions |
|---|---|
Starting a task |
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Full migration |
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Incremental migration |
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Precautions for Comparison |
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Prerequisites¶
You have logged in to the DRS console.
For details about the DB types and versions supported by real-time migration, see Real-Time Migration.
You have read Suggestions and Precautions.
Procedure¶
This section uses MongoDB sharded clusters as an example to describe how to configure a task for migrating MongoDB databases to DDS over a public network.
On the Online Migration Management page, click Create Migration Task.
On the Create Replication Instance page, specify the task name, description, and the replication instance details, and click Next.
Task information description
Table 5 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.
Project
The project corresponds to the current region and can be changed.
Task Name
The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).
Description
The description consists of a maximum of 256 characters and cannot contain special characters
!=<>'&"\Replication instance information
Table 6 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 in the same region.
Public network is suitable for migrations from on-premises or external cloud databases to the destination databases bound with an EIP.
VPN and Direct Connect are 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.
Destination Database Access
This option does not appear if the DDS kernel version does not support this setting. This setting cannot be changed after a migration task is created.
Read-only
During migration, the destination database is read-only. After the migration is complete, it restores to the read/write status. This option ensures the integrity and success rate of data migration.
Read/Write
During migration, the destination database can be queried or modified. Data may be modified when operations are performed or applications are connected. It should be noted that background processes can often generate or modify data, which may result in data conflicts, task faults, and upload failures. Do not select this option if you do not fully understand the risks. Set the destination database to Read/Write only when you need to modify other data in the database during the migration.
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.
Tags
Table 7 Tags¶ Parameter
Description
Tags
Tags a task. This configuration is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 20 tags.
After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.
Note
If a task fails to be created, DRS retains the task for three days by default. After three days, the task automatically ends.
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
Table 8 Source database information¶ Parameter
Description
mongos IP Address or Domain Name
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 - 65535
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.
Database 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 SSL is disabled, 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.
Note
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
Table 9 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.
Note
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.
On the Set Task page, select migration objects and click Next.
Table 10 Migrate Object¶ Parameter
Description
Flow Control
You can choose whether to control the flow.
Yes
You can customize the maximum migration speed.
In addition, you can set the time range based on your service requirements. The traffic rate setting usually includes setting of a rate limiting time period and a traffic rate value. Flow can be controlled all day or during specific time ranges. The default value is All day. A maximum of three time ranges can be set, and they cannot overlap.
The flow rate must be set based on the service scenario and cannot exceed 9,999 MB/s.
No
The migration speed is not limited and the outbound bandwidth of the source database is maximally used, which causes read consumption on the source database accordingly. For example, if the outbound bandwidth of the source database is 100 MB/s and 80% bandwidth is used, the I/O consumption on the source database is 80 MB/s.
Note
Flow control mode takes effect only during a full migration.
If you select Cluster for Source DB Instance Type and oplog for Obtain Incremental Data in 2, the flow control settings will be synchronized to each subtask.
You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.
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.
If an object name contains spaces, 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 name of the selected migration object cannot contain spaces.
To quickly select the desired database objects, you can use the search function.
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.
If the check is complete and the check success rate is 100%, click Next.
Note
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.
On the Confirm Task page, specify Start Time and confirm that the configured information is correct and click Submit to submit the task.
Table 11 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.
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.