Backfill Execution

After the Metadata Migration has been completed; begin the backfill of documents from the snapshot of the source cluster.

Document Migration

Once started, a fleet of workers will spin up to read the snapshot and reindex documents on the target cluster. This fleet of workers can be scaled to increased the speed that documents are reindexed onto the target cluster.

CloudWatch Metrics & Dashboard

The Migration Assistant creates a CloudWatch Dashboard you can use to visualize the health and performance of the backfill process. It brings together the metrics for the backfill workers and, for those migrating to Amazon OpenSearch Service, the target cluster.

You can find the Backfill dashboard in the AWS Console for CloudWatch Dashboards, in the region you have deployed the Migration Assistant. The metric graphs for your target cluster will be blank until you select the OpenSearch Domain you're migrating to from the drop-down menu at the top of the Dashboard.

Check the starting state of the clusters

You can see the indices and rough document counts of the source and target cluster by running the cat-indices command. This can be used to monitor the difference between the source and target for any migration scenario. Check the indices of both clusters with the following command:

console clusters cat-indices

Example cat-indices command output

SOURCE CLUSTER
health status index       uuid                   pri rep docs.count docs.deleted store.size pri.store.size
green  open   my-index WJPVdHNyQ1KMKol84Cy72Q   1   0          8            0     44.7kb         44.7kb

TARGET CLUSTER
health status index                        uuid                   pri rep docs.count docs.deleted store.size pri.store.size
green  open   .opendistro_security         N3uy88FGT9eAO7FTbLqqqA   1   0         10            0     78.3kb         78.3kb

Start the backfill

By starting the backfill by running the following command, which creates a fleet with a single worker:

console backfill start

Monitor the status

You can use the status check command to see more detail about things like the number of shards completed, in progress, remaining, and the overall status of the operation:

console backfill status --deep-check

Example status output

BackfillStatus.RUNNING
Running=1
Pending=0
Desired=1
Shards total: 48
Shards completed: 48
Shards incomplete: 0
Shards in progress: 0
Shards unclaimed: 0

Note

The status will be "RUNNING" even if all the shards have been migrated.

Scale up the fleet

To speed up the transfer, you can scale the number of workers. It may take a few minutes for these additional workers to come online. The following command will update the worker fleet to a size of ten:

console backfill scale 5

Pausing the migration

If you need to pause the migration, you do so using the command:

console backfill pause

This will spin down any and all existing workers while leaving the backfill operation in a state it can be restarted. When it's time to restart the migration, you can run console backfill start or just scale up the worker count to your desired number with console backfill scale <worker_count>.

Stopping the migration

Backfill requires manually stopping the migration. Stopping the migration spins down any and all workers and cleans up all metadata used to track and coordinate the migration. Once the status checks report your data has been complete migrated, you can stop the migration with the command:

console backfill stop

Example stop output

Backfill stopped successfully.
Service migration-aws-integ-reindex-from-snapshot set to 0 desired count. Currently 0 running and 5 pending.
Archiving the working state of the backfill operation...
RFS Workers are still running, waiting for them to complete...
Backfill working state archived to: /shared-logs-output/migration-console-default/backfill_working_state/working_state_backup_20241115174822.json

You cannot restart a stopped migration. If you want to pause a migration, use console backfill pause instead.

Troubleshooting

How to scaling the fleet

It is recommended to scale up the fleet slowly while monitoring the health metrics of the Target Cluster to avoid over-saturating it. Amazon OpenSearch Domains provide a number of metrics and logs that can provide this insight; refer to the official documentation on the subject ↗. The AWS Console for Amazon Opensearch Service surfaces details that can be useful for this as well.

Related Links

• Technical details for RFS