> For the complete documentation index, see [llms.txt](https://docs.lenses.io/latest/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lenses.io/latest/k2k/configuration-reference/observability.md).

# Observability

Metrics prefixes and exporter configuration.

To operate a replication pipeline, we need to know whether it is keeping up, which partitions are assigned, and when something fails. Kafka exposes broker metrics but not replication-specific signals, therefore K2K exports replication and JVM metrics through **Kafka** (for [Lenses HQ](https://lenses.io)), **OTLP**, and **Prometheus**.

Enable export with the `--telemetry` flag and standard `OTEL_*` environment variables; see [Command-line options](/latest/k2k/deployment.md#command-line-options). Customize name prefixes under `metrics.prefix`. For the metrics control topic, see [Topic creation](/latest/k2k/configuration-reference/topic-creation.md). Record lineage headers are separate; see [Record tracing](/latest/k2k/configuration-reference/record-tracing.md). For the Kafka metrics topic name, see the [Advanced](#advanced) section below.

## Prerequisites

* [License accepted](/latest/k2k/configuration-reference/licenses.md)
* [Kafka connectivity and authentication](/latest/k2k/configuration-reference/kafka-connectivity-authentication.md)
* At least one metrics exporter configured (Kafka with Lenses HQ, OTLP, or Prometheus)

## Example

```yaml
name: "my_pipeline"
source:
  kafka:
    common:
      "bootstrap.servers": "source:9092"
    consumer:
      "group.id": "my-k2k-group"
target:
  kafka:
    common:
      "bootstrap.servers": "target:9092"
metrics:
  prefix:
    assignment: "myapp.k2k."
replication:
  - source:
      topic: "orders.*"
  - sink:
      topic: source
      partition: source
```

## Configuration keys

Each prefix is prepended to the metrics emitted by one Kafka client or subsystem. **Defaults differ per application** — the offset mapper ships its own set, so the same key resolves differently depending on which application reads the pipeline.

| Key                               | Description                                   | Required | Replicator default      | Offset mapper default                 |
| --------------------------------- | --------------------------------------------- | -------- | ----------------------- | ------------------------------------- |
| `metrics.prefix.sourceConsumer`   | Metric prefix for the source consumer         | No       | `k2k.consumer.source.`  | (not used)                            |
| `metrics.prefix.targetConsumer`   | Metric prefix for the target control consumer | No       | `k2k.consumer.control.` | `k2k.offsetmapping.consumer.control.` |
| `metrics.prefix.targetProducer`   | Metric prefix for the target producer         | No       | `k2k.producer.`         | `k2k.offsetmapping.producer.`         |
| `metrics.prefix.assignment`       | Metric prefix for assignment metrics          | No       | `k2k.`                  | (not used)                            |
| `metrics.prefix.offsetMappingApp` | Metric prefix for offset mapper metrics       | No       | (not used)              | `k2k.offsetmapping.`                  |

When building dashboards or alerts across both applications, query the offset mapper under its `k2k.offsetmapping.` prefixes rather than the replicator defaults.

## Metric names

### K2K metrics

K2K emits these replication metrics under the `metrics.prefix.assignment` prefix (default `k2k.`, so the full name of the first is `k2k.topics-assigned`):

| Metric                | Meaning                                                 |
| --------------------- | ------------------------------------------------------- |
| `topics-assigned`     | Source topics currently assigned to this instance       |
| `partitions-assigned` | Source partitions currently assigned to this instance   |
| `offset-commit`       | Replication progress commits recorded in control topics |

Use `partitions-assigned` to confirm work is spread across instances — see [Horizontal scaling](/latest/k2k/configuration-reference/horizontal-scaling.md).

### Tags

K2K metrics carry these tags:

| Tag                | Meaning                                      |
| ------------------ | -------------------------------------------- |
| `source_topic`     | Topic name on the source Kafka cluster       |
| `source_partition` | Partition number on the source Kafka cluster |
| `target_topic`     | Topic name on the target Kafka cluster       |
| `target_partition` | Partition number on the target Kafka cluster |

Kafka client metrics passed through from the consumer, producer, and admin clients keep their standard Kafka names (`records-lag`, `records-consumed-rate`, `record-send-rate`, and so on) under the matching prefix, tagged with `topic` and `partition`. For their meaning, see the [Apache Kafka monitoring reference](https://kafka.apache.org/documentation/#monitoring).

JVM and runtime metrics are exported by the OpenTelemetry runtime instrumentation under their standard names.

## Advanced

### Kafka metrics topic

When using the Kafka metrics exporter with Lenses HQ, metrics are written to a control topic on the target Kafka cluster.

| Key                   | Description                    | Required | Default         | Used by    |
| --------------------- | ------------------------------ | -------- | --------------- | ---------- |
| `metrics.kafka.topic` | Topic for Kafka metrics export | No       | `__k2k_metrics` | Replicator |

For auto creating this topic with custom settings, see [Topic creation](/latest/k2k/configuration-reference/topic-creation.md).


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