> 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-memory-hog.md).

# Pod memory hog

Pod memory hog is a Kubernetes pod-level chaos fault that allocates a configurable amount of memory inside a target container for a configurable duration. The allocation is contained inside the selected container, so the kernel enforces any `resources.limits.memory` you have configured. If the allocation pushes the container past its limit, the OOM killer terminates a process inside the container — usually the application itself. Sibling containers and other pods on the node are not directly affected unless the node itself runs out of memory.

Use this fault to test how a service responds when one or more replicas suddenly consume far more memory than expected: a memory leak, a runaway cache, an unexpectedly large request payload, or a JVM heap surge.

{% 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:

* **OOM behavior:** When the container exceeds its memory limit, does the kernel `OOMKill` it cleanly? Does Kubernetes restart it with the correct backoff? Does the workload converge or enter a crash loop?
* **Memory-based autoscaling:** Does the HorizontalPodAutoscaler scale out within your window when memory utilization crosses the target threshold, and does it scale back in once the fault ends?
* **Eviction order on the node:** When the node experiences memory pressure (because a `Burstable` pod blew through its request), does the kubelet evict `BestEffort` and over-quota pods first, leaving `Guaranteed` pods running?
* **Request handling under pressure:** Do callers degrade gracefully, retry effectively, or amplify the failure when a replica becomes memory-bound?
* **JVM and runtime tuning:** Does the JVM's `-Xmx` (or Go's `GOGC`, or Node's `--max-old-space-size`) match the container's memory limit? An over-provisioned heap forces OOM kills before the GC reclaims memory.

***

### 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 pods are Running:** The application pods you intend to target are in the `Running` state before the fault is launched.
* **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.
* **Workload selector defined:** The chaos experiment knows the target workload (`Deployment`, `StatefulSet`, `DaemonSet`, `Rollout`, etc.) by kind, namespace, and either names or labels.

***

### 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 memory hog to an experiment in Chaos Studio. Defaults are shown for reference.

**Chaos parameters**

| Tunable                | Description                                                                                           | Default |
| ---------------------- | ----------------------------------------------------------------------------------------------------- | ------- |
| `MEMORY_CONSUMPTION`   | Amount of memory to allocate inside the target container, in megabytes (1 MB = 10<sup>6</sup> bytes). | `500`   |
| `NUMBER_OF_WORKERS`    | Number of memory worker threads used to perform the allocation. Increase for faster ramp-up.          | `1`     |
| `TOTAL_CHAOS_DURATION` | Duration of the fault in seconds.                                                                     | `30`    |

**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 to stress. 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`                               |

Tunables that apply to every chaos 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="warning" %}
**PICK MEMORY\_CONSUMPTION CAREFULLY**

If `MEMORY_CONSUMPTION` plus the container's normal working set exceeds the container's `resources.limits.memory`, the kernel `OOMKill`s the container. Whether this is desired depends on what you are testing. To raise pressure without triggering OOM, set `MEMORY_CONSUMPTION` to roughly `(limit - baseline) * 0.8`.
{% 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>

Allocates a specified amount of memory inside the target container for the configured duration, with the allocation bounded by any `resources.limits.memory` set on the container; if the limit is breached, the kernel OOM-kills a process inside the container.

***

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

* The container's memory usage rises rapidly to the configured `MEMORY_CONSUMPTION` plus baseline.
* If the container has no memory limit and the node has free memory, the allocation succeeds and the workload may continue normally.
* If the container has a memory limit and the allocation exceeds it, the kernel triggers an OOM kill inside the cgroup. The container restarts with `Last State: OOMKilled`.
* If multiple replicas are targeted and the node is small, the node itself can enter `MemoryPressure`. The kubelet starts evicting `BestEffort` and over-request pods.
* HPA controllers configured on memory metrics scale out, with the usual sync and stabilization delays.
* Liveness probes that allocate memory themselves may fail under pressure, accelerating restart.

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

After `TOTAL_CHAOS_DURATION`, the allocation is freed and the container's memory usage returns to baseline. If the container was OOM-killed during the run, the new container restarts at baseline.
{% 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:

* **Container memory and OOM kills:** Watch `container_memory_working_set_bytes` and pod restart count. Use a [Prometheus probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/apm-probes.md) to fail when restarts cross a threshold.
* **HPA behavior:** Track `kube_hpa_status_current_replicas` vs `kube_hpa_status_desired_replicas`. Use a [Prometheus probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/apm-probes.md) to fail if scale-out does not happen within your SLO.
* **Application health:** Use an [HTTP probe](/resilience-testing/chaos-engineering/use-chaos-engineering/probes/http-probe.md) for direct endpoint health; latency and error rate signal whether callers degrade or amplify.

***

### 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 that memory pressure is reaching the target container:

1. **Watch memory usage on the target pod.**

   ```bash
   kubectl top pod -n <namespace> <pod-name> --containers
   ```

   The targeted container's memory should rise to `MEMORY_CONSUMPTION` plus its baseline working set.
2. **Look for OOM kill events (if the container hit its limit).**

   ```bash
   kubectl describe pod -n <namespace> <pod-name> | grep -A 3 'Last State'
   ```

   `Reason: OOMKilled` confirms the kernel terminated the container.

***

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

* **End of duration:** The allocation is freed automatically and container memory drops back to baseline within seconds.
* **OOM kill during the run:** The container is restarted by the kubelet. The replacement container starts fresh; no manual cleanup is needed.
* **Abort the experiment:** Stopping the experiment from Chaos Studio triggers the same cleanup path.
* **Persistent restart loop:** If the workload's normal memory footprint exceeds its limit (independently of chaos), the OOM kill recurs and the pod enters `CrashLoopBackOff`. Lower `MEMORY_CONSUMPTION` or raise the container's memory limit.

***

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

This fault is not appropriate in the following scenarios:

* **Serverless Kubernetes (EKS Fargate, ACI virtual nodes):** These platforms do not allow the privileged access this 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 containers only.
* **Containers with a very small memory limit:** A container limited to `64Mi` cannot absorb the default `500` MB allocation; the OOM kill fires immediately and you cannot observe steady-state pressure. Lower `MEMORY_CONSUMPTION` to a value below the limit.
* **Pods using `hostNetwork` or `hostPID`:** These bypass the standard namespace model and the fault may behave unexpectedly.

***

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

<details>

<summary>Pod memory hog 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, insufficient memory on the node, or a PodSecurity admission policy blocking privileged pods. Add the required tolerations to the experiment or run in a namespace with privileged Pod Security level.

</details>

<details>

<summary>Memory usage on the target container does not rise during pod-memory-hog</summary>

The most common causes are: MEMORY\_CONSUMPTION smaller than the container's headroom, so the allocation completes too quickly to observe; NUMBER\_OF\_WORKERS too low so the allocation paces below your monitoring scrape interval; or TARGET\_CONTAINER does not match any container in the pod. Verify with kubectl get pod -o jsonpath='{.spec.containers\[\*].name}' and raise MEMORY\_CONSUMPTION.

</details>

<details>

<summary>Container is OOMKilled immediately for pod-memory-hog in Harness Chaos Engineering</summary>

MEMORY\_CONSUMPTION plus the container's existing working set exceeds its resources.limits.memory. The kernel triggers an OOM kill before the fault can run steady-state. Lower MEMORY\_CONSUMPTION below (limit - baseline), or raise the container memory limit. If the immediate OOM kill is what you wanted to test, that is the expected outcome.

</details>

<details>

<summary>Connection to container runtime fails for pod-memory-hog 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. Confirm the path by SSHing to the node and running ls -l on each candidate socket file.

</details>

***

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

* [Pod CPU hog](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/pod/pod-cpu-hog.md): Apply CPU pressure to a container instead of memory pressure.
* [Node memory hog](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/kubernetes/node/node-memory-hog.md): Apply memory pressure to the entire node rather than a single container.
* [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.