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From MongoDB to DDS

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Язык статьи: Английский

Supported Source and Destination Databases

Table 1 Supported databases
Source DB	Destination DB
On-premises MongoDB (versions 3.2, 3.4, 3.6, 4.0, 4.2, 4.4 and 5.0) ECS-hosted MongoDB (versions 3.2, 3.4, 3.6, 4.0, 4.2, 4.4 and 5.0) Other Cloud MongoDB 3.2, 3.4, 3.6, 4.0, 4.2, 4.4 and 5.0 DDS DB instances (versions 3.2, 3.4, 4.0, 4.2, 4.4 and 5.0) NOTE: If the source database is a DDS 3.2 cluster instance, only full migration is supported. If the source database is a DDS DB instance, the source DB engine is DDS. Otherwise, the source DB engine is MongoDB-DDS.	DDS DB instances (versions 3.4, 4.0, 4.2, 4.4, and 5.0) NOTE: The destination database version must be the same as or later than the source database version.

You can run the following command to query a database version.

db.version()

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 2. DRS automatically checks the database account permissions in the pre-check phase and provides handling suggestions.

Table 2 Database account permission
Type	Full Migration	Full+Incremental Migration
Source database user	Replica set: The source database user must have the readAnyDatabase permission for the admin database. Single node: The source database user must have the readAnyDatabase permission for the admin database. Cluster: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the config database. To migrate accounts and roles of the source database, the source and destination database users must have the read permission for the system.users and system.roles system tables of the admin database.	Replica set: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the local database. Single node: The source database user must have the readAnyDatabase permission for the admin database and the read permission for the local database. Cluster: The source mongos node user must have the readAnyDatabase permission for the admin database and the read permission for the config database. The source shard node user must have the readAnyDatabase permission for the admin database and the read permission for the local database. To migrate accounts and roles of the source database, the source and destination database users must have the read permission for the system.users and system.roles system tables of the admin database.
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

You are advised to create an independent database account for DRS task connection to prevent task failures caused by database account password modification.
After changing the account passwords for the source and destination databases, modify the connection information of the DRS task by referring to Modifying Connection Information to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.
For a replica set instance, the source database user must have the readAnyDatabase permission for the admin database and the read permission for the local database.
```
db.grantRolesToUser("Username",[{role:"readAnyDatabase",db:"admin"}, {role:"read",db:"local"}])
```
For a cluster instance, the source database mongos 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"}])
```

Supported Migration Objects

Different types of migration tasks support different migration objects. For details, see Table 3. DRS will automatically check the objects you selected before the migration.

Table 3 Migration objects
Type	Precautions
Migration objects	You can select table-, database-, or instance-level (all-level) migration. Replica set: Only collections (including validator and capped collections), indexes, and views can be migrated. Cluster: Only collections (including validator and capped collections), shard keys, indexes, and views can be migrated. Single node: Only collections (including validator and capped collections), indexes, and views can be migrated. Only user data and source database account information can be migrated. The system databases (for example, local, admin, and config) and system collection cannot be migrated. If service data is stored in the system database, run the renameCollection command to move the service data to the user database. The statement for creating a view cannot contain a regular expression. Collections that contain the _id field without indexes are not supported. The first parameter of BinData() cannot be 2. If ranged sharding is used, maxKey cannot be used as the primary key. Do not store non-UTF-8 character strings in the String field of the source database collection. Otherwise, data will be inconsistent before and after the migration. If the source database is a cluster instance of version 4.4 or later and the destination database version is earlier than 5.0, composite hash shard keys and composite hash indexes are not supported. If the destination database version is 5.0, composite hash shard keys and composite hash indexes are supported. If the source database is a replica set instance of version 4.4 or later and the destination database version is earlier than 5.0, composite hash indexes are not supported. If the destination database version is 5.0, composite hash indexes are supported. Time series collections are not supported in both the full and incremental phases. Cluster shard keys cannot be synchronized during incremental synchronization.

Log Configuration Check on the Source Database

During an incremental migration, Oplog of the source database must be enabled. If the storage space is sufficient, store the source database Oplog for as long as possible. The recommended retention period is at least three days.

Precautions

To ensure tasks can run normally, DRS provides automatic pre-check. Before starting a DRS task, DRS checks the configurations and conditions of the source and destination databases. For details about the main check items and handling suggestions, see DRS Pre-Check Items. In addition to the pre-check items, you need to pay attention to the items listed in Table 4.

Table 4 Precautions
Type	Restrictions
Restrictions on the source database	The source cannot be a GeminiDB Mongo instance. The source database name cannot contain /\.$ or spaces. The collection name and view name cannot start with system. or contain the dollar sign ($). When multiple source databases are migrated to the same destination database, the name of the database to be migrated must be unique. Replica set: The MongoDB replica set instance must be available and have primary nodes. If you need to perform an incremental migration for a single node instance, the source database must be a DDS single-node instance on the current cloud.
Restrictions on usage	General During the migration, do not modify or delete the usernames, passwords, and permissions of the source and destination databases or change the ports of the source and destination databases. During migration, do not modify the destination database (including but not limited to DDL and DML operations) that is being migrated. During migration, data rollback caused by a primary/standby switchover of the source database is not supported. During the migration, documents larger than 16 MB in the source database cannot be inserted or updated. During the migration, do not run sh.moveChunk() on the source database. Otherwise, the migrated data will be inconsistent. Full migration During task startup and full migration, do not perform DDL operations on the source database. Otherwise, the task may be abnormal. Incremental migration During an incremental migration of collections, you are advised not to rename the collections. To ensure the migration performance, concurrent replay is performed at the set level in the incremental task phase. In the following scenarios, only single-thread write is supported and concurrent replay is not supported: The collection index contains a unique key. The value of capped of the collection attribute is true. In either of the preceding scenarios, the task delay may increase. Data comparison You are advised to compare data during off-peak hours of the source database to prevent inconsistent data from being falsely reported and reduce the impact on the source database and DRS tasks. During incremental synchronization, if data is written to the source database, the comparison results may be inconsistent. During row comparison, if an orphan document exists in a cluster instance or chunks are being migrated, the number of returned rows is incorrect and the comparison results are inconsistent. For details, see MongoDB official documents.
Other restrictions	If the source database is not on a cluster instance, the following operations and commands are supported during incremental migration: Creating and deleting databases Adding, deleting, and updating documents Creating and deleting collections Creating and deleting indexes Creating and deleting views The convertToCapped, collMod, and renameCollection commands are supported. During a full+incremental migration between clusters or from a cluster to a replica set, the objects to be migrated cannot be deleted. Otherwise, the migration task fails. If you select Cluster (MongoDB 4.0+) for Source DB Instance Type, DRS will use the MongoDB change streams feature during the migration. Note the following before you use change streams: Data subscription using change streams consumes a certain amount of CPU and memory resources of the source database. Evaluate the resources of the source database in advance. If the load on the source database is heavy, the processing speed of change streams cannot keep up with the oplog generation speed. As a result, DRS synchronization delay occurs. Due to the restrictions of MongoDB change streams, only drop database, drop collection, and rename DDL statements are supported during incremental synchronization. When documents are inserted or replaced in a collection of the source database for the first time, indexes of the collection will be synchronized to the destination database. If you do not need to synchronize indexes, contact technical support. The DBPointer and DBRef data types are not supported. In the incremental migration phase,the migration speed can reach up to 10,000 rows in a single table per second. The changeStream method is in restricted use. If Source DB Instance Type is set to Cluster and Obtain Incremental Data is set to oplog, DRS will create multiple subtasks based on the number of source shards. If Flow Control is enabled, the configured rate limit value is synchronized to each subtask. If a Time-to-Live (TTL) index already exists in the collection of the source database or is created during an incremental migration, data consistency cannot be ensured when source and destination databases are in different time zones or clocks. The value of block_compressor is determined by stats().wiredTiger.creationString.block_compressor of the collection in the source database. If the destination database contains corresponding empty collections, the compression parameters will not be migrated. If the compression parameters in the source database are not supported by the destination database, configure the compression parameters based on net.compression.compressors of the destination database. If the destination database version is DDS 4.2, DRS does not migrate compression parameters because the destination database does not support compression parameter settings. If the accounts and roles to be migrated conflict with those in the destination database, DRS will skip the conflict data and continue the migration. If the MongoDB service of the source database is deployed with other services on the same server, set the value of the cacheSizeGB parameter to the half of the minimum idle cache for the WiredTiger engine of the source database. If the source is a replica set instance, enter information about all primary and secondary nodes to reduce the impact of a primary/secondary switchover on the migration task. If you enter information about multiple primary and secondary nodes, ensure that all nodes belong to the same replica set instance. If the source is a cluster instance, enter information about multiple mongos nodes to reduce the impact of single-node failure on the migration task. In addition, ensure that all mongos nodes belong to the same cluster instance. For an incremental migration of a cluster instance, you are advised to enter information about all primary and secondary nodes of the shard node and ensure that all node information belongs to the same shard to reduce the impact of a primary/secondary switchover on the migration task. Ensure that all shard nodes belong to the same cluster. In some migration scenarios, to prevent the drop database operation from deleting the existing collections in the destination database, the drop database operation will not be synchronized to the destination database. If the source database version is earlier than MongoDB 3.6, running the drop database command will delete the collections only from the source database. The collections in destination database will not be deleted. If the source database version is MongoDB 3.6 or later, the drop database operation is represented by the drop database and drop collection operations in oplog. Running the drop database command will delete the collections from both the source and destination databases. To accelerate the migration, delete unnecessary indexes from the source database and retain only necessary indexes before the migration. You are advised not to create indexes for the source database during the migration. If indexes must be created, create them in the background. To prevent loopback, do not start tasks that migrate the same database to and out of the cloud at the same time.

Procedure

This section uses a MongoDB sharded cluster as an example to describe how to configure a task for migrating data from MongoDB 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 Create Now.

Task information description

Table 5 Task information
Parameter	Description
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 can contain up to 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 between cloud databases of the same account in the same region and VPC. Public network is suitable for migrations from on-premises databases or external cloud databases to destination databases. VPN or Direct Connect is suitable for migrations from on-premises databases to cloud databases or between databases across regions on the cloud using a VPN, Direct Connect, Cloud Connect, VPCEP, or a VPC peering connection.
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 Subnets 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	If Source DB Instance Type is set to Cluster and Migration Mode is set to Full+Incremental, you need to determine how to capture data changes during the incremental synchronization. Also, the balancer of the source database must be disabled and orphaned documents must be deleted. For details, see 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 need to enter the connection information of each shard in the source database when testing the connection between the source database and the DRS instance. 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.
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 64. Specify this parameter based on the actual number of shards in the source DB.
Specify EIP	This parameter is available when you select Public network for Network Type. Select an EIP to be bound to the DRS instance. DRS will automatically bind the specified EIP to the DRS instance and unbind the EIP after the task is complete. If Source DB Instance Type is set to Cluster and Obtain Incremental Data is set to oplog, the number of specified EIPs must be consistent with that of source shards.

AZ
Table 7 Task AZ
Parameter
Description
AZ
Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.

Table 7 Task AZ
Parameter	Description
AZ	Select the AZ where you want to create the DRS task. Selecting the one housing the source or destination database can provide better performance.

Enterprise Project and Tags

Table 8 Enterprise Project and Tags
Parameter	Description
Enterprise Project	An enterprise project you would like to use to centrally manage your cloud resources and members. Select an enterprise project from the drop-down list. The default project is default.
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 stops.

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 9 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 of the source MongoDB database user. For example: The default authentication database of DDS instance is admin.
mongos Username	The username of the mongos node of the source MongoDB database. For example, the default mongos username of a DDS instance is rwuser.
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 shard node information of the MongoDB database based on the number of cluster shard nodes in the source database. Set the IP address or domain name of the sharded database to that of the shard node in the source MongoDB database. The value is in the IP address/Domain name:Port format. Set the authentication database of the sharded database to the name of the database to which the shard node account of the source MongoDB database belongs. For example, the default shard authentication database of a DDS instance is admin. Set the username of the sharded database to that of the shard node in the source MongoDB database. For example, the default shard username of a DDS instance is sharduser.

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 10 Destination database settings
Parameter	Description
DB Instance Name	The DB instance you selected when creating the migration task. This parameter cannot be changed.
Authentication Database	The name of the authentication database. For example: The default authentication database of DDS instance is admin.
Database Username	The username for accessing the destination 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.

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 11 Migrate Object
Parameter	Description
Flow Control	You can choose whether to control the flow. Flow Control takes effect in the full phase only. Yes You can set a maximum migration speed, which varies depending on network conditions. During the migration, the migration speed of each task (or each subtask in multi-task mode) will not exceed the threshold you configure. 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 Always. A maximum of 10 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. 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	The left pane displays the source database objects, and the right pane displays the selected objects. 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 displayed page, specify Start Time, Send Notifications, SMN Topic, Delay Threshold (s), Run Post-Migration Comparison, Start Now (Initialization Only), and Stop Abnormal Tasks After, confirm that the configured information is correct, and click Submit to submit the task.

Table 12 Task startup settings
Parameter	Description
Start 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	This parameter is optional. If the status, latency metric, or data of the migration task is abnormal, DRS will send you a notification.
SMN Topic	This parameter is available only after you enable Send Notifications and create a topic on the SMN console and add a subscriber.

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.
- After the full migration is complete, you can use data comparison to check whether the data is consistent before and after the migration.
- By default, DRS retains a task in the Configuration state for three days. After three days, DRS automatically deletes background resources, but the task status remains unchanged. When you reconfigure the task, DRS applies for resources again.
- For a public network task, DRS needs to delete background resources after you stop the task. The EIP bound to the task cannot be restored to the Unbound state until background resources are deleted.

Parent topic: To the Cloud

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