Migration Scenarios and Use Cases
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You can use Relational Migrator to migrate one legacy application at a time to MongoDB. Depending on your application's needs, you can migrate either with or without downtime.
Migrate during Scheduled Downtime
If your application does not require constant uptime, such as in the case of an internal application, you can have the migration occur during scheduled downtime. Migrating during downtime is the easiest way to configure and complete the migration process.
When you start the migration process, Relational Migrator takes a snapshot of the data on the legacy application and migrates the data from that point in time. During the migration process, your legacy application can remain online to support incoming reads, but cannot support incoming writes. The length of the migration process depends on several factors, such as the amount of data being migrated and your connection speed.
After the migration completes, take your legacy application offline and launch your new application.
Migrate without Downtime
If your application must remain online to support reads and writes during the migration process, you can use Change Data Capture (CDC) to migrate data without downtime. This process is called a continuous sync migration.
When you start a continuous sync migration, Relational Migrator takes a snapshot of the data on the legacy application and tracks database updates in near real time. During the migration process, your source and destination databases remain in sync.
After the continuous sync migration completes, you can transfer users to the new application and shut down the legacy application.
To learn more about sync jobs, see Sync Jobs.
Currently Unsupported Migration Scenarios
Relational Migrator currently does not support the following migration scenarios:
Migrating multiple applications through a phased migration without downtime. In this scenario, multiple legacy applications are decommissioned and migrated to the new database while the original database still supports writes. The migration uses CDC to keep the legacy application in sync with the destination database.
Migrating an operational data store. Depending on your workload, this scenario could involve CDC running indefinitely without completing.
The preceding scenarios require long-running CDC, or in some cases involve CDC running indefinitely. Therefore, these scenarios are not recommended with Relational Migrator.
Relational Migrator will support more migration scenarios and use cases in future releases.