> For the complete documentation index, see [llms.txt](https://developer.harness.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.harness.io/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-jvm-kafka-latency.md).

# Pod JVM Kafka latency

Pod JVM Kafka latency is a Kubernetes pod-level chaos fault that adds a configurable delay to Kafka client calls from a JVM running in a target container, scoped to a chosen topic and client mode, for a configurable duration. Only matched calls are slowed; other Kafka traffic and other code paths run at normal speed. When the fault ends, Kafka calls return to baseline latency immediately.

Use this fault to test how a Java service behaves when Kafka becomes slow on a specific code path: a partition leader that takes longer to ack produces, a consumer side processing messages slowly, or a degraded cluster on one topic.

{% hint style="info" %}
**RUN YOUR FIRST EXPERIMENT**

If you have not configured the chaos infrastructure yet, go to [Quickstart](/resilience-testing/chaos-engineering/new-to-chaos-engineering/quickstart.md) to install the chaos infrastructure and run an experiment end to end.
{% endhint %}

***

### Use cases <a href="#use-cases" id="use-cases"></a>

Run this fault when you want to answer concrete questions like:

* **Producer timeout sensitivity:** When `send().get()` takes 2 seconds instead of 50 ms, does the application respect `request.timeout.ms` and shed load, or does it block?
* **Consumer lag growth:** Slow consumer-side processing and verify whether the application catches up after the fault or rebalances.
* **In-flight buffer pressure:** Slow producer ack and see whether `buffer.memory` fills up and triggers application-level back-pressure.
* **End-to-end SLO impact:** Does the added Kafka latency push request p99 over your SLO, or does the design absorb it?
* **Circuit breaker behavior:** Does a circuit breaker around the slow operation trip and recover correctly when the fault ends?

***

### Prerequisites <a href="#prerequisites" id="prerequisites"></a>

* **Kubernetes version:** 1.21 or later. Go to [What's supported](/resilience-testing/chaos-engineering/new-to-chaos-engineering/whats-supported.md) to confirm distribution support.
* **Target pod is Running:** The Java application pod is in the `Running` state.
* **Java agent attach available:** The Java process allows agent attach. Utilities such as `ps`, `pgrep`, and `bash` are present in the container, and the JVM is not built with a restricted runtime that strips attach modules.
* **Kafka client in classpath:** The target JVM uses the Apache Kafka Java client and produces to or consumes from the configured `KAFKA_TOPIC` in the configured `KAFKA_MODE`.
* **Privileged pods allowed:** The cluster lets you schedule privileged pods in the chaos namespace. GKE Autopilot supports this fault but requires the one-time setup in [Chaos on GKE Autopilot](/resilience-testing/chaos-engineering/use-chaos-engineering/gke-autopilot.md); other locked-down distributions may need similar exemptions.
* **Container runtime access:** The chaos pod can reach the container runtime socket on the target node (`/run/containerd/containerd.sock`, `/var/run/docker.sock`, or `/var/run/crio/crio.sock`).
* **Workload selector defined:** The chaos experiment knows the target workload by kind, namespace, and either names or labels.

{% hint style="info" %}
**JVM CHAOS USES THE BYTEMAN AGENT**

This fault attaches a [Byteman](https://byteman.jboss.org/) agent to the target JVM over `BYTEMAN_PORT`. The port must be reachable from the chaos pod and must not be in use by the application.
{% endhint %}

***

### Supported environments <a href="#supported-environments" id="supported-environments"></a>

| Platform                                 | Support status                                                                                                 |
| ---------------------------------------- | -------------------------------------------------------------------------------------------------------------- |
| Amazon EKS                               | Supported                                                                                                      |
| Azure AKS                                | Supported                                                                                                      |
| Google GKE                               | Supported                                                                                                      |
| Red Hat OpenShift                        | Supported                                                                                                      |
| Rancher                                  | Supported                                                                                                      |
| VMware Tanzu                             | Supported                                                                                                      |
| Self-managed Kubernetes (CNCF-certified) | Supported                                                                                                      |
| GKE Autopilot                            | Supported with [Autopilot setup](/resilience-testing/chaos-engineering/use-chaos-engineering/gke-autopilot.md) |
| EKS Fargate, ACI virtual nodes           | Not supported (no access to container runtime sockets)                                                         |

***

### Permissions required <a href="#permissions-required" id="permissions-required"></a>

The fault runs under the chaos infrastructure's service account.

| Resource (`apiGroup`)                                               | Verbs                                                                    | Why it is needed                                            |
| ------------------------------------------------------------------- | ------------------------------------------------------------------------ | ----------------------------------------------------------- |
| `pods` (`""`)                                                       | `get`, `list`, `create`, `delete`, `deletecollection`, `patch`, `update` | Discover target pods and run the chaos pod on the same node |
| `pods/log` (`""`)                                                   | `get`, `list`, `watch`                                                   | Stream chaos pod logs for status and debugging              |
| `deployments`, `statefulsets`, `replicasets`, `daemonsets` (`apps`) | `get`, `list`                                                            | Resolve the target workload to the pods it owns             |
| `events` (`""`)                                                     | `get`, `list`, `create`, `patch`, `update`                               | Record fault progress as Kubernetes events                  |
| `jobs` (`batch`)                                                    | `get`, `list`, `create`, `delete`, `deletecollection`                    | Run the chaos job that drives the fault                     |

The default Harness chaos infrastructure service account already includes these permissions.

***

### Fault tunables <a href="#fault-tunables" id="fault-tunables"></a>

Configure the following fault parameters when you add Pod JVM Kafka latency to an experiment in Chaos Studio. Defaults are shown for reference.

**Kafka filters**

| Tunable                  | Description                                                                                                        | Default      |
| ------------------------ | ------------------------------------------------------------------------------------------------------------------ | ------------ |
| `KAFKA_MODE`             | Client mode to target. One of `producer` (publish-side) or `consumer` (subscribe-side).                            | `"producer"` |
| `KAFKA_TOPIC`            | Target Kafka topic name. Empty matches all topics for the configured mode.                                         | `""`         |
| `TRANSACTION_PERCENTAGE` | Percentage of matched Kafka operations to delay, between `0` and `100`. `0` delays none; `100` delays every match. | `0`          |

**Chaos parameters**

| Tunable                | Description                                              | Default |
| ---------------------- | -------------------------------------------------------- | ------- |
| `LATENCY`              | Delay to add to each matched operation, in milliseconds. | `2000`  |
| `TOTAL_CHAOS_DURATION` | Duration of the fault in seconds.                        | `60`    |

**JVM**

| Tunable        | Description                                                                                                   | Default |
| -------------- | ------------------------------------------------------------------------------------------------------------- | ------- |
| `BYTEMAN_PORT` | Port on which the Byteman agent listens inside the container. Must not conflict with any port already in use. | `9091`  |
| `JAVA_HOME`    | Absolute path to the Java installation inside the container. Empty auto-detects from `PATH`.                  | `""`    |

**Targeting**

| Tunable                   | Description                                                                                                          | Default    |
| ------------------------- | -------------------------------------------------------------------------------------------------------------------- | ---------- |
| `TARGET_PODS`             | Comma-separated list of pod names to target. Empty selects from the workload's pods using `POD_AFFECTED_PERCENTAGE`. | `""`       |
| `TARGET_CONTAINER`        | Container in the pod running the JVM. Empty targets the first container in the pod spec.                             | `""`       |
| `NODE_LABEL`              | Label selector to filter target pods by the node they run on. Empty disables node-based filtering.                   | `""`       |
| `POD_AFFECTED_PERCENTAGE` | Percentage of the workload's pods to target. `0` means one pod.                                                      | `0`        |
| `SEQUENCE`                | When multiple pods are targeted, inject `parallel` (all at once) or `serial` (one after another).                    | `parallel` |

**Runtime and helper**

| Tunable             | Description                                                                                                                                                                                                      | Default                           |
| ------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------- |
| `CONTAINER_RUNTIME` | Container runtime on the target nodes. One of `containerd`, `docker`, `crio`.                                                                                                                                    | `containerd`                      |
| `SOCKET_PATH`       | Path to the container runtime socket on the target node. Set to match `CONTAINER_RUNTIME`.                                                                                                                       | `/run/containerd/containerd.sock` |
| `RAMP_TIME`         | Wait period in seconds before and after the fault. Go to [ramp time](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/common-tunables-for-all-faults.md#ramp-time) to read how it is applied. | `0`                               |

Common pod selection tunables (`TARGET_WORKLOAD_KIND`, `TARGET_WORKLOAD_NAMESPACE`, `TARGET_WORKLOAD_NAMES`, `TARGET_WORKLOAD_LABELS`) are documented in [common pod fault tunables](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/common-tunables-for-pod-faults.md). Tunables that apply to every fault are documented in [common tunables for all faults](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/common-tunables-for-all-faults.md).

{% hint style="info" %}
**MATCH MODE TO SCENARIO**

Producer-side latency surfaces as slow `send().get()` and increased in-flight buffer use. Consumer-side latency surfaces as slow `poll()` returns and growing lag. Target the mode that matches the failure you want to validate.
{% endhint %}

#### Configure for your container runtime <a href="#configure-for-your-container-runtime" id="configure-for-your-container-runtime"></a>

Set `CONTAINER_RUNTIME` and `SOCKET_PATH` to match the runtime on the target node:

| `CONTAINER_RUNTIME`    | `SOCKET_PATH`                     |
| ---------------------- | --------------------------------- |
| `containerd` (default) | `/run/containerd/containerd.sock` |
| `docker`               | `/var/run/docker.sock`            |
| `crio`                 | `/var/run/crio/crio.sock`         |

***

### Fault execution in brief <a href="#fault-execution-in-brief" id="fault-execution-in-brief"></a>

Attaches a Java agent to the target JVM and intercepts Kafka client operations matching `KAFKA_MODE` and `KAFKA_TOPIC` to add `LATENCY` milliseconds to each matched call on the configured percentage, for `TOTAL_CHAOS_DURATION` seconds.

***

### Expected behavior during fault execution <a href="#expected-behavior-during-fault-execution" id="expected-behavior-during-fault-execution"></a>

* Matched Kafka operations take longer by approximately `LATENCY` ms. Other topics and the unmatched mode run normally.
* Caller-side metrics (request latency, in-flight buffer use, consumer lag) rise to reflect the added delay.
* Clients with timeouts shorter than `LATENCY` cancel the call and may retry.
* Consumer applications may see growing lag if `LATENCY` per poll exceeds the processing budget.
* Tracing systems show the matched Kafka span growing by `LATENCY` ms.

{% hint style="info" %}
**WHEN THE FAULT ENDS**

Kafka calls return to baseline latency immediately. Calls in flight finish at the delayed time and then the system returns to normal.
{% endhint %}

#### Signals to watch <a href="#signals-to-watch" id="signals-to-watch"></a>

Attach [resilience probes](/resilience-testing/chaos-engineering/use-chaos-engineering/probes.md) to assert each layer:

* **Producer latency:** Use a [Prometheus probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/apm-probes.md) on `kafka_producer_request_latency_avg`.
* **Consumer lag:** Use a Prometheus probe on `kafka_consumer_lag` or your dashboard's lag metric.
* **End-to-end latency:** Use an [HTTP probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/http-probe.md) against an endpoint that triggers a produce or consume.

***

### Verify the fault execution effect <a href="#verify-the-fault-execution-effect" id="verify-the-fault-execution-effect"></a>

While the experiment is running, confirm operations are slower:

1. **Time a request that triggers the matched operation.**

   ```bash
   kubectl run -n <namespace> tester --image=nicolaka/netshoot --rm -it -- \
     curl -w "time=%{time_total}\n" -o /dev/null -s http://<service>:<port>/<endpoint>
   ```
2. **Confirm in tracing.**

   The Kafka span for the matched operation should be approximately `LATENCY` ms longer than its baseline.

***

### Recovery and cleanup <a href="#recovery-and-cleanup" id="recovery-and-cleanup"></a>

* **End of duration:** Kafka calls return to baseline latency automatically.
* **Abort the experiment:** Stopping the experiment from Chaos Studio triggers the same cleanup path.
* **Lag drainage:** Consumer lag built up during the fault may take time to drain. Allow normal processing to catch up, or scale consumers temporarily if needed.

***

### Limitations <a href="#limitations" id="limitations"></a>

* **Serverless Kubernetes (EKS Fargate, ACI virtual nodes):** These platforms do not expose container runtime sockets and reject the privileged access the fault needs. GKE Autopilot is supported once the one-time setup in [Chaos on GKE Autopilot](/resilience-testing/chaos-engineering/use-chaos-engineering/gke-autopilot.md) is in place.
* **Windows containers:** This fault is supported on Linux pods only.
* **Non-JVM and non-Kafka workloads:** This fault targets the Apache Kafka Java client inside a JVM.
* **Streams API:** Applications using Kafka Streams may attribute latency to internal operators rather than client calls; behavior depends on the topology.

***

### Troubleshooting <a href="#troubleshooting" id="troubleshooting"></a>

<details>

<summary>Pod JVM Kafka latency experiment stays Pending or never starts in Harness Chaos Engineering</summary>

Inspect the chaos pods in the experiment namespace with kubectl describe pod -n . The most common causes are taints on the target node that the chaos pods do not tolerate, insufficient resources, or a PodSecurity admission policy blocking privileged pods. Add the required tolerations or run in a namespace with privileged Pod Security level.

</details>

<details>

<summary>No latency observed during pod-jvm-kafka-latency</summary>

The most common causes are: KAFKA\_MODE does not match what the application uses (producer vs consumer); KAFKA\_TOPIC does not match the topic the application produces/consumes; TRANSACTION\_PERCENTAGE is 0 (default); or the path uses Kafka Streams. Re-run with TRANSACTION\_PERCENTAGE=100, empty KAFKA\_TOPIC, and a larger LATENCY to confirm.

</details>

<details>

<summary>Connection to container runtime fails for pod-jvm-kafka-latency in Harness Chaos Engineering</summary>

The default SOCKET\_PATH is /run/containerd/containerd.sock. For Docker, set CONTAINER\_RUNTIME=docker and SOCKET\_PATH=/var/run/docker.sock. For CRI-O, set CONTAINER\_RUNTIME=crio and SOCKET\_PATH=/var/run/crio/crio.sock.

</details>

***

### Related faults <a href="#related-faults" id="related-faults"></a>

* [Pod JVM Kafka exception](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-jvm-kafka-exception.md): Throw an exception from Kafka client calls instead of slowing them.
* [Pod JVM Solace latency](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-jvm-solace-latency.md): Solace equivalent for the Solace Java client.
* [Pod JVM method latency](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-jvm-method-latency.md): Generic Java method-level latency injection.
* [Common pod fault tunables](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/common-tunables-for-pod-faults.md): Shared environment variables for selecting target pods and workloads.