Migrate data from an ApsaraDB RDS for MySQL instance to an Elasticsearch cluster - Data Transmission Service

This topic describes how to migrate data from an ApsaraDB RDS for MySQL instance to an Elasticsearch cluster by using Data Transmission Service (DTS).

Prerequisites

The destination Elasticsearch cluster is created. For more information, see Create an Alibaba Cloud Elasticsearch cluster.
The available storage space of the destination Elasticsearch cluster is larger than the total size of the data in the source ApsaraDB RDS for MySQL instance. This ensures successful full data migration.

Limits

Note

During schema migration, DTS migrates foreign keys from the source database to the destination database.
During full data migration and incremental data migration, DTS temporarily disables the constraint check and cascade operations on foreign keys at the session level. If you perform the cascade and delete operations on the source database during data migration, data inconsistency may occur.


Category	Description
Limits on the source database	The tables to be migrated must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination cluster may contain duplicate data records. If you select tables as the objects to be migrated and you need to modify the tables in the destination cluster, such as renaming tables or columns, you can migrate up to 5,000 tables in a single data migration task. If you run a task to migrate more than 5,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to migrate the tables in batches or configure a task to migrate the entire database. The binary logging feature must be enabled for the ApsaraDB RDS for MySQL instance. The binlog_format parameter must be set to row and the binlog_row_image parameter must be set to full. For more information, see View the parameters of an ApsaraDB RDS for MySQL instance. Otherwise, error messages are returned during the precheck and the data migration task cannot be started. If you perform only incremental data migration, the binary logs of the source instance must be stored for more than 24 hours. If you perform schema migration and incremental data migration, the binary logs of the source instance must be stored for at least seven days. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. After schema migration is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. For more information about the binary log files of an ApsaraDB RDS for MySQL instance, see View and delete the binary log files of an ApsaraDB RDS for MySQL instance. Limits on operations: During schema migration, do not perform DDL operations to change the schemas of databases or tables. Otherwise, the data migration task fails.
Other limits	If you want to add columns to a table in the source instance, modify the mappings of the index that corresponds to the table in the Elasticsearch cluster. Then, perform DDL operations on the source table, pause the data migration task, and then start the task again. Before you migrate data, evaluate the impact of data migration on the performance of the source instance and destination cluster. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses the read and write resources of the source instance and destination cluster. This may increase the loads on the database servers. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination cluster. After full data migration is complete, the size of used tablespace of the destination cluster is larger than that of the source instance. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination cluster, stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination cluster. Otherwise, the data in the source instance overwrites the data in the destination cluster after a failed task is resumed. If a table that you want to migrate contains empty strings, the data that contains empty strings in the table is written to the Elasticsearch cluster as data of the LONG type. In this case, the data migration task fails. If a table that you want to migrate contains latitude and longitude values that are stored in reverse, an error occurs when the data in the table is written to the Elasticsearch cluster.

Billing


Migration type	Instance configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Schema migration
Data Transmission Service (DTS) migrates the schemas of objects from the source database to the destination database.
Full data migration
DTS migrates the existing data of objects from the source database to the destination database.
Incremental data migration
After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting services of self-managed applications during data migration.

SQL operations that can be incrementally migrated


Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE

Data type mappings

The data types of MySQL databases and Elasticsearch clusters do not have one-to-one correspondence. During initial schema migration, DTS converts the data types of the source database into the data types of the destination cluster. For more information, see Data type mappings between heterogeneous databases.

The following table lists the mapping between terms in Elasticsearch and relational databases.


Elasticsearch	Relational database
index	database
type	table
document	row
field	column
mapping	schema

Permissions required for database accounts


Database	Schema migration	Full data migration	Incremental data migration	References
ApsaraDB RDS for MySQL instance	SELECT permission	SELECT permission	REPLICATION SLAVE, REPLICATION CLIENT, SHOW VIEW, and SELECT permissions	Create an account on an ApsaraDB RDS for MySQL instance
Elasticsearch cluster	Read and write permissions on the objects to be migrated. The default database account in Elasticsearch clusters is elastic.

Procedure

Go to the Data Migration Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Migration.
Note
- Operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Configure the DMS console based on your business requirements.
- You can also go to the Data Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

Click Create Task. On the page that appears, 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 to identify the task. You do not need to use a unique task name.
Source Database	Select Instance	Select whether to use an existing instance. If you select an existing instance, DTS automatically applies the parameter settings of the instance. You do not need to configure the corresponding parameters again. If you do not use an existing instance, you must configure parameters for the source database.
	Database Type	The type of the source database. Select MySQL.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source ApsaraDB RDS for MySQL instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	RDS Instance ID	The ID of the source ApsaraDB RDS for MySQL instance.
	Database Account	The database account of the source ApsaraDB RDS for MySQL instance. For information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
	Database Password	The password of the database account.
	Encryption	Specifies whether to encrypt the connection to the database. You can select Non-encrypted or SSL-encrypted based on your business requirements. If you want to select SSL-encrypted, you must enable SSL encryption for the ApsaraDB RDS for MySQL instance before you configure the data synchronization task. For more information, see Configure SSL encryption for an ApsaraDB RDS for MySQL instance.
Destination Database	Select Instance	Select whether to use an existing instance. If you select an existing instance, DTS automatically applies the parameter settings of the instance. You do not need to configure the corresponding parameters again. If you do not use an existing instance, you must configure parameters for the source database.
	Database Type	The type of the destination database. Select Elasticsearch.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination Elasticsearch cluster resides.
	Instance ID	The ID of the destination Elasticsearch cluster.
	Database Account	The account that is used to connect to the Elasticsearch cluster. This account is the Username parameter that you specified when you created the Elasticsearch cluster. The default database account in Elasticsearch clusters is elastic.
	Database Password	The password of the database account.

In the lower part of the page, click Test Connectivity and Proceed.
If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance, and you must make sure that the ECS instance can access the database. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database. For more information about the CIDR blocks of DTS servers, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
Warning If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database or an instance, or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhance the security of your username and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Select objects for the task and configure advanced settings.


Parameter	Description
Migration Types	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, Full Data Migration, and Incremental Data Migration. Note If Incremental Data Migration is not selected, we recommend that you do not write data to the source instance during data migration. This ensures data consistency between the source and destination instances.
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 migration 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 tables that have identical 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, DTS does not migrate data records that have the same primary keys as data records in the destination database. If the source and destination databases have different schemas, only some columns are migrated or the data migration task fails. Proceed with caution.
Index Name	If you select Table Name, the index created in the destination Elasticsearch cluster uses the same name as the table in the ApsaraDB RDS for MySQL instance. If you select Database Name_Table Name, the index created in the destination Elasticsearch cluster is concatenated in the format of Database name_Table name. Note The index name mapping rule takes effect for all tables.
Capitalization of Object Names in Destination Instance	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 ensure that the capitalization of object names is consistent with the default capitalization of object names in 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 icon to add the objects to the Selected Objects section.
Selected Objects	To modify the names of the migrated fields, right-click the name of the table in the Selected Objects section. In the dialog box that appears, specify the index name and type name of the table in the destination Elasticsearch cluster, and then click OK. For more information, see Map the name of a single object. Note Specify SQL conditions to filter data. Only the data records that meet the specified conditions are migrated to the destination cluster. For more information, see Use SQL conditions to filter data.

Click Next: Advanced Settings to configure advanced settings.


Parameter	Description
Set Alerts	Specifies whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications. Valid values: No: does not set alerts. Yes: sets alerts. If you select Yes, you must also set the alert threshold and alert contacts. For more information, see Configure monitoring and alerting when you create a DTS task.
Retry Time for Failed Connection	The retry time range for failed connections. If the data migration task fails, DTS immediately retries to establish a connection within the retry time range. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the parameter to a value greater than 30. If DTS reconnects to the source instance and destination cluster within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you set different retry time ranges for multiple data migration tasks that have the same source instance or destination cluster, the value that is set later 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 instance and destination cluster are released.
Shard Configuration	The number of primary shards and replica shards based on the shard configuration of indexes of the destination Elasticsearch cluster.
String Index	The method used to compile strings to the indexes of the destination Elasticsearch cluster. analyzed: The strings are analyzed before indexing. You must select a specific analyzer. For more information about the analyzer types, see Built-in analyzer reference. not analyzed: The strings are indexed with the original values. no: The strings are not indexed.
Time Zone	The time zone of the date and time data types such as DATETIME and TIMESTAMP, which you can select during the data migration to the destination Elasticsearch cluster. Note If the date and time data types in the destination cluster do not need a time zone, you must specify the document type for the date and time data types.
DOCID	The default value of the parameter is the primary key of the table in the Elasticsearch cluster. If the table does not have a primary key, the value of the parameter is the ID column that is automatically generated by Elasticsearch.
Configure ETL	Specifies whether to configure the extract, transform, and load (ETL) feature. For more information, see What is ETL?. Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.

In the lower part of the page, click Next: Configure Database and Table Fields. On the page that appears, set the _routing policy and _id value for the tables that you want to migrate to the destination Elasticsearch cluster.


Category	Description
Set _routing.	Specifies whether to store a document on a specific shard of the destination Elasticsearch cluster. For more information, see _routing. If you select Yes, you can specify custom columns for routing. If you select No, the _id value is used for routing. Note If the version of the destination Elasticsearch cluster is 7.`x`, you must select No.
_routing Column	The column that is used for routing. Note This parameter is required only if the Set _routing parameter is set to Yes.
Value of _id	The column that is used to store the IDs of documents.

In the lower part of the page, click Next: Save Task Settings and Precheck.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the causes, run a precheck again.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issues. Then, run a precheck again.
  If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, specify the Instance Class parameter for the data migration instance. The following table describes the parameter.


Section	Parameter	Description
Parameters	Instance Class	DTS provides several instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

Read and select the check box for Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.