reverse

Description

Reverses the direction of a committed sync operation.

For example:

• You have a COMMITTED sync operation.

• cluster0 is the source and cluster1 is the destination.

• After the sync operation is COMMITTED, new writes occur only on the destination cluster. The source cluster will not accept new writes.

In this scenario, you can use the reverse endpoint to sync writes from cluster1 to cluster0, including any writes that occurred on cluster1 after mongosync reached canWrite=true. To check the canWrite status during sync, use the /progress endpoint.

For more information and a tutorial on using the reverse endpoint, see Reverse Sync Direction.

Requirements

To use the reverse endpoint:

• mongosync must be configured when the initial sync begins. The call to the /start API endpoint must set:

  • reversible to true

  • enableUserWriteBlocking to true.

You cannot update these options after the sync starts.

• mongosync must be in the COMMITTED state.

• The destination cluster oplog must not roll over between mongosync reaching canWrite=true and receiving the /reverse request.

• The source and destination clusters must have the same number of shards. You cannot reverse sync when the clusters have different topologies.

• The source and destination clusters must run the same MongoDB major version.

• The user specified in the mongosync connection string must have the required permissions on the source and destination clusters. The permissions vary depending on your environment and if you want to modify write-blocking settings or use reverse sync.

 db.<collection>.aggregate( [
   { $collStats: { storageStats: { } } },
   { $project: { "storageStats.indexDetails.<field_name>.metadata.formatVersion": 1 } }
 ] )

[
  {
    storageStats: {
      indexDetails: { <field_name>: { metadata: { formatVersion: 14 } } }
    }
  }
]

Request

POST /api/v1/reverse 

Response

Example

The following example reverses the direction of a committed sync operation.

curl localhost:27182/api/v1/reverse -XPOST --data '{ }'

{"success":true}

Behavior

The reverse endpoint starts the REVERSING state. mongosync swaps the source and destination clusters and resumes applying change events.

If the reverse sync is successful, mongosync enters the RUNNING state. The synchronization continues in the reverse direction from the original sync job. You do not need to restart the entire sync process to copy the original data.

To view the mapping direction for the synchronization of the source and destination clusters, use the progress endpoint and check the directionMapping object.