> 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-method-exception.md).

# Pod JVM method exception

Pod JVM method exception is a Kubernetes pod-level chaos fault that causes a specific Java method in a JVM running in a target container to throw a configurable exception on every invocation for a configurable duration. Only the named method is affected; all other code paths run normally. When the fault ends, the method returns to its normal behavior immediately.

Use this fault to test how callers and dependents react when a specific method starts throwing: a database wrapper that raises a connection error, a third-party SDK call that fails, or a business-logic method that hits an invariant.

{% 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:

* **Caller exception handling:** Does the calling code catch the exception, propagate it, or crash the thread?
* **Retry semantics:** Does the caller honor a retry budget, or do retries amplify load on the rest of the system?
* **Circuit breaker tripping:** Does a circuit breaker around the failing method open after the configured failure threshold and short-circuit subsequent calls?
* **Trace and log coverage:** Does the failure surface in tracing and logs with enough context to be diagnosable in production?
* **Compensating transactions:** For multi-step business operations, do rollback paths complete cleanly when one step fails?

***

### 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.
* **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 method exception to an experiment in Chaos Studio. Defaults are shown for reference.

**Required parameters**

| Tunable     | Description                                                                                                  | Default    |
| ----------- | ------------------------------------------------------------------------------------------------------------ | ---------- |
| `CLASS`     | Fully qualified class name containing the target method (for example `com.example.payments.PaymentService`). | (required) |
| `METHOD`    | Name of the method to throw the exception from.                                                              | (required) |
| `EXCEPTION` | Fully qualified exception class to throw (for example `java.lang.IllegalStateException`).                    | (required) |

**Chaos parameters**

| Tunable                | Description                       | Default |
| ---------------------- | --------------------------------- | ------- |
| `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" %}
**PICK THE RIGHT EXCEPTION TYPE**

Choose an exception that the caller can plausibly receive in production (for example `java.sql.SQLException` for a database wrapper, `java.io.IOException` for a network helper). Picking an unrelated exception type often surfaces uncaught-exception bugs that would not happen in real failures.
{% 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 instruments `CLASS.METHOD` so that each invocation throws an instance of `EXCEPTION` for `TOTAL_CHAOS_DURATION` seconds.

***

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

* Every call to the named method raises the configured exception. Other methods run normally.
* Direct callers surface the failure as caught exceptions, error responses, or queued retries depending on the framework.
* Tracing systems show the method span ending in error; downstream calls that depended on the method's return value do not happen for failed invocations.
* Error dashboards see a spike in the configured exception type.

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

The method returns to its normal behavior immediately. Cached state (open circuits, exhausted retry budgets) in callers may take additional time to reset.
{% 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:

* **Method-level error rate:** Use a [Prometheus probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/apm-probes.md) on the method's error counter to confirm the injection took effect.
* **Caller error rate:** Use an [HTTP probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/http-probe.md) against endpoints that exercise the method to detect 5xx spikes.
* **Application logs:** Use a [command probe](/resilience-testing/chaos-testing/probes/command-probe.md) to grep container logs for the injected exception's class name.

***

### 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 the method is throwing:

1. **Exercise the method from a client.**

   ```bash
   kubectl run -n <namespace> tester --image=nicolaka/netshoot --rm -it -- \
     curl -s http://<service>:<port>/<endpoint-that-calls-the-method>
   ```

   The response should reflect the failure.
2. **Confirm the exception in logs.**

   ```bash
   kubectl logs -n <namespace> <target-pod> --tail=200 | grep <EXCEPTION>
   ```

   The configured exception class should appear in stack traces.

***

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

* **End of duration:** The method returns to its normal behavior automatically.
* **Abort the experiment:** Stopping the experiment from Chaos Studio triggers the same cleanup path.
* **Stuck state:** If a downstream circuit breaker stays open or a retry budget is exhausted, follow the application's recovery procedure or restart the pod.

***

### 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 processes:** This fault targets a Java process.
* **Inlined or intrinsified methods:** Methods that the JIT compiler has inlined may not be interceptable; consider running with `-XX:-Inline` for verification.
* **Method overloads:** Only the method name is matched. If multiple overloads share a name, all are affected for the duration.

***

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

<details>

<summary>Pod JVM method exception 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 exception observed during pod-jvm-method-exception</summary>

The most common causes are: CLASS or METHOD does not match (verify the fully qualified class name and case-sensitive method name); the method is JIT-inlined and not interceptable; the wrong container is targeted (set TARGET\_CONTAINER explicitly); or JAVA\_HOME is not detectable. Re-run with EXCEPTION set to a common type like java.lang.IllegalStateException to confirm the path is working.

</details>

<details>

<summary>Connection to container runtime fails for pod-jvm-method-exception 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 method latency](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-jvm-method-latency.md): Add latency to a Java method instead of throwing.
* [Pod JVM modify return](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-jvm-modify-return.md): Modify the return value of a Java method.
* [Pod application function error](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-application-function-error.md): Language-agnostic function-level error for instrumented applications.
* [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.