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Live Migrate Your Replica Set to Atlas

Atlas can perform a live migration of a source replica set to an Atlas cluster, keeping the cluster in sync with the remote source until you cut your applications over to the Atlas cluster. Once you reach the cutover step in the following procedure, you should stop writes to the source cluster by stopping your application instances, pointing them to the Atlas cluster, and restarting them.

To begin, click on the ellipsis … button and choose Migrate Data to this Cluster from the dropdown menu.

Note

On the Cluster list, the ellipsis … button appears beneath the cluster name, as shown below. When you view a cluster’s details, the ellipsis … appears on the right-hand side of the screen, next to the Connect and Configuration buttons.

Note

You cannot select an M0 (Free Tier) or M2/M5 shared cluster as the source or destination for live migration. To migrate data from an M0 (Free Tier) or M2/M5 shared cluster to a paid cluster, see Modify a Cluster.

For a procedure on live migrating a sharded cluster, see Live Migrate Your Sharded Cluster to Atlas.

Prerequisites

Upgrade Path

Atlas live migration supports the following migration paths:

Source Replica Set MongoDB Version	Destination Atlas Replica Set MongoDB Version
2.6	3.4, 3.6, 4.0
3.0	3.4, 3.6, 4.0
3.2	3.4, 3.6, 4.0
3.4	3.4, 3.6, 4.0
3.6	3.6, 4.0
4.0	4.0

Important

Users migrating from a MongoDB 2.6 cluster should take particular care to update and test their applications in context of the destination Atlas cluster. In general, whenever migrating to a newer version of MongoDB, plan for updating and testing your application in context of the destination migration cluster.

Network Access

Source Cluster Firewall Must Allow Access from Live Migration Server

Atlas Live Migration process streams data through a MongoDB-controlled application server. Atlas provides the IP ranges of the MongoDB Live Migration servers during the Live Migration process. Grant these IP ranges access to your source cluster to allow connectivity to the MongoDB Live Migration server.

Atlas Cluster IP Whitelist Must Allow Access From Your Application Servers

Atlas only allows connections to a cluster from entries in the project’s whitelist. You must add IP addresses such as application servers to the project whitelist manually. Do this before beginning the migration procedure.

Atlas temporarily adds the IP address of the Atlas migration servers to the project whitelist. During the migration procedure, you cannot edit or delete this entry. Atlas removes the entry automatically once the procedure completes.

For documentation on adding entries to the Atlas whitelist, see Configure Whitelist Entries.

Pre-Migration Validation

Atlas performs a number of validation checks on the source and destination cluster before starting the Live Migration procedure.

• The source cluster is a replica set.

  If the source is a standalone, convert the standalone to a replica set first before using Live Migration.

• The destination Atlas cluster must be a replica set.

Source Cluster Security

Atlas only supports SCRAM for connecting to source clusters enforcing authentication.

If the source cluster enforces authentication, create a user with the following privileges:

• Read all databases and collections. The readAnyDatabase role on the admin database covers this requirement.
• Read the oplog.
• Run the getParameter command.

Various built-in roles provide sufficient privileges. For example:

• For source clusters running MongoDB version 3.4+ a user must have, at a minimum, both clusterMonitor and readAnyDatabase roles. For example:

  copy

  use admin
  db.createUser(
    {
      user: "mySourceUser",
      pwd: "mySourceP@$$word",
      roles: [ "clusterMonitor", "readAnyDatabase" ]
    }
  )
  

• For source clusters running MongoDB version 3.2 a user must have, at a minimum, both clusterManager and readAnyDatabase roles. For example:

  copy

  use admin
  db.createUser(
    {
      user: "mySourceUser",
      pwd: "mySourceP@$$word",
      roles: [ "clusterManager", "readAnyDatabase" ]
    }
  )
  

• For source clusters running MongoDB version 2.6 or 3.0 a user must have, at a minimum, the readAnyDatabase role. For example:

  copy

  use admin
  db.createUser(
    {
      user: "mySourceUser",
      pwd: "mySourceP@$$word",
      roles: [ "readAnyDatabase" ]
    }
  )
  

Specify the user name and password to Atlas when prompted by the Live Migration procedure.

If the source cluster uses a different authentication mechanism, to connect you can use the Migrate with mongomirror tool to migrate data from the source cluster to the destination Atlas cluster.

Index Key Limits

If your MongoDB deployment contains indexes with keys which exceed the index key limit, you must set the MongoDB server parameter failIndexKeyTooLong to false before starting the Live Migration procedure.

Note

Modifying indexes so that they contain no oversized keys is preferable to setting the failIndexKeyTooLong server parameter to false. See the server manual for strategies on dealing with oversized index keys.

Considerations

Destination Cluster Configuration

When configuring the destination cluster, consider the following:

• The live migration process streams data through a MongoDB-managed application server. Each server runs on infrastructure hosted in the nearest region to the source cluster. The following regions are available:

  Europe

  • Ireland
  • Frankfurt
  • London

  Americas

  • Eastern US
  • Western US

  APAC

  • Sydney

• Due to network latency, the live migration process may not be able to keep up with a source cluster that has an extremely heavy write load. In this situation, you can still migrate directly from the source cluster by pointing the mongomirror tool to the destination Atlas cluster.

• The live migration process may not be able to keep up with a source cluster whose write workload is greater than what can be transferred and applied to the destination cluster. You may need to scale the destination cluster up to a tier with more processing power, bandwidth or disk IO.

• The destination Atlas cluster must be a replica set.

• You cannot select an M0 (Free Tier) or M2/M5 shared-tier cluster as the destination for live migration.

• Do not change the featureCompatibilityVersion flag while Atlas Live Migrate is running.

MongoDB Users and Roles

Atlas does not migrate any user or role data to the destination cluster.

If the source cluster enforced authentication, you must re-create the credentials used by your applications on the destination Atlas cluster. Atlas uses SCRAM for user authentication. See Configure MongoDB Users for a tutorial on creating MongoDB users in Atlas.

Avoid Namespace Changes

You should not make any namespace changes during the migration process, such as using the renameCollection command or executing an aggregation pipeline that includes the $out aggregation stage.

Rolling Restarts

After the migration process is complete, your destination replica set will restart each of its members one at a time. This is called a rolling restart, and as a consequence, a failover will occur on the primary. To ensure a smooth migration, it is recommended that you perform a Test Failover procedure prior to migrating your data to the destination cluster.

Migrate Your Cluster

Staging and Production Migrations

Consider performing this procedure twice. Perform a partial migration that stops at the Perform the Cutover step first. This creates an up-to-date Atlas-backed staging cluster to test application behavior and performance using the latest driver version that supports the MongoDB version of the Atlas cluster.

Once you have tested your application, perform the full migration procedure using a separate Atlas cluster to create your Atlas-backed production environment.

Important

Avoid making changes to the source cluster configuration while the Live Migration procedure runs, such as removing replica set members or modifying mongod runtime settings like featureCompatibilityVersion.

Pre-Migration Checklist

Before starting the import process:

• If you don’t already have a destination cluster, create a new Atlas deployment and configure it as needed. For complete documentation on creating an Atlas cluster, see Tutorial: Create a New Cluster.

• After your Atlas cluster is deployed, ensure that you can connect to it from all client hardware where your applications run. Testing your connection string helps ensure that your data migration process can complete with minimal downtime.

  1. Download and install the mongo shell on a representative client machine, if you don’t already have it.
  2. Connect to your destination cluster using the connection string from the Atlas UI. For more information, see Connect via mongo Shell.

  Once you have verified your connectivity to your target cluster, start the import procedure.

Procedure

1

Start the migration process.

1. Click the ellipsis … button for the destination Atlas cluster. On the Cluster list, the ellipsis … button appears beneath the cluster name, as shown below. When you view a cluster’s details, the ellipsis … appears on the right-hand side of the screen, next to the Connect and Configuration buttons.

   

2. Click Migrate Data to this Cluster.

3. Atlas displays a walk-through screen with instructions on how to proceed with the live migration. The process copies the data from your source cluster to the new target cluster. After you complete the walk-through, you can point your application to the new cluster.

   You will need the following details for your source cluster to facilitate the migration:

   • The hostname and port of the source cluster’s primary member
   • The username and password used to connect to the source cluster
   • If the source cluster uses TLS/SSL and is not using a public Certificate Authority (CA), you will need the source cluster’s CA file.

   Prepare the information as stated in the walk-through screen, then click I’m Ready To Migrate.

4. Atlas displays a walk-through screen that collects information required to connect to the source cluster.

   • Atlas displays the IP address of the MongoDB application server responsible for your live migration at the top of the walk-through screen. Configure your source cluster firewall to grant access to the displayed IP address.

   • Enter the hostname and port of the primary member of the source cluster into the provided text box. For example, mongoPrimary.example.net:27017.

   • If the source cluster enforces authentication, enter a username and password into the provided text boxes.

     See Source Cluster Security for guidance on the user permissions required by Atlas live migration.

   • If the source cluster uses TLS/SSL, toggle the SSL button.

   • If the source replica set uses TLS/SSL and is not using a public Certificate Authority (CA), copy the contents of the source cluster’s CA file into the provided text box.

   • If you wish to drop all collections on the target cluster before beginning the migration process, toggle the switch marked Clear any existing data on your target cluster? to Yes.

5. Click Validate to confirm that Atlas can connect to the source replica set.

   If validation fails, check that:

   • You have whitelisted Atlas on your source cluster.
   • The provided user credentials, if any, exist on the source cluster and have the required permissions.
   • The SSL toggle is enabled only if the source cluster requires it.
   • The CA file provided, if any, is valid and correct.

6. Click Start Migration to start the migration process.

   Once the migration process begins, the Atlas UI displays the Migrating Data walk-through screen for the destination Atlas cluster. This walk-through screen updates as destination cluster proceeds through the migration process, as well as the time remaining for the destination cluster to sync with the source cluster.

When the migration timer and the Prepare to Cutover button turn green, proceed to the next step.

2

Perform the cutover.

When Atlas detects that the source and destination clusters are nearly in sync, it starts an extendable 72 hour timer to begin the cutover procedure. If the 72 hour period passes, Atlas stops synchronizing with the source cluster. You can extend the time remaining by 24 hours by clicking the Extend time hyperlink below the <time> left to cut over timer.

1. Once you are prepared to cut your applications over to the destination Atlas cluster, click Prepare to Cutover.
2. Atlas displays a walk-through screen with instructions on how to proceed with the cutover. These steps are also outlined below:
   1. Stop your application. This ensures that no additional writes are generated to the source cluster.
   2. Wait for the optime gap to reach zero. When the counter reaches zero, the source and destination clusters are in sync.
   3. Restart your application using the new connection string provided in step 3 of the Live Migrate cutover UI.
3. Once you have completed the cutover procedure and confirmed your applications are working normally with the Atlas cluster, click Cut Over to complete the migration procedure. This allows Atlas to:
   • Mark the migration plan as complete.
   • Remove the Application Server subnets from the destination cluster whitelist.
   • Remove the MongoDB user that Live Migrate used to import data to the destination cluster.

Migration Support

If you have any questions regarding migration support beyond what is covered in this documentation, or if you encounter an error during migration, please request support through the Atlas UI.

To file a support ticket:

1. Click Support in the left-hand navigation.
2. Click Request Support.
3. For Issue Category, select Help with live migration.
4. For Priority, select the appropriate priority. For questions, please select Medium Priority. If there was a failure in migration, please select High Priority.
5. For Request Summary, please include Live Migration in your summary.
6. For More details, please include any other relevant details to your question or migration error.
7. Click the Request Support button to submit the form.

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