# Monitor replication from self-managed Kafka clusters
<a name="msk-replicator-monitor-external"></a>

After you create an MSK Replicator to replicate data from an self-managed Apache Kafka cluster to Amazon MSK Express brokers, monitor the following Amazon CloudWatch metrics to track replication progress and determine when your applications are ready to migrate.

**Monitor Replicator creation status**  
After calling the `CreateReplicator` API, the Replicator transitions through the following states: `CREATING`, `RUNNING`, or `FAILED`. Allow approximately 30 minutes.

```
aws kafka describe-replicator --replicator-arn <replicator-arn>
```

**Monitor data replication**  
Monitor the following metrics to track data replication progress:
+ `MessageLag` — Monitor until it reaches 0, which indicates all data has been replicated.
+ `ReplicationLatency` — Track the time it takes for records to replicate from source to target.
+ `ReplicationFailures` — Should be 0. A non-zero value indicates replication issues.

**Monitor consumer group offset synchronization**  
When `synchroniseConsumerGroupOffsets` is set to `true`, MSK Replicator periodically translates and synchronizes consumer group offsets from the source to the target cluster.
+ `ConsumerGroupCount` — Verify that this matches the expected number of consumer groups being synchronized.
+ `ConsumerGroupOffsetSyncFailure` — Should be 0. If greater than 0, check that consumer groups are active, verify Read and Describe permissions, and ensure topics exist on the target cluster.
+ `OffsetLag (MSK)` and `OffsetLag (Non-MSK)` — Compare partition-level consumer lag across both clusters to verify offsets are synchronized.

**Determine migration readiness**  
Your applications are ready to migrate when all of the following conditions are met:
+ `MessageLag` = 0
+ `ReplicationFailures` = 0
+ `ConsumerGroupOffsetSyncFailure` = 0