> 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/cloud-foundry/cf-app-network-duplication.md).

# CF app network duplication

CF app network duplication is a Cloud Foundry chaos fault that duplicates `packetDuplicationPercentage` percent of egress packets from one or more instances of `app`. You can restrict the duplication to specific destination hosts, IP ranges, source ports, or destination ports. The fault lasts for `duration` seconds.

Use this fault to validate idempotency assumptions at the application layer (HTTP requests, database writes, message-bus consumers) and to test that the receiver's protocol layer handles duplicates correctly without amplifying the noise.

{% 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 Linux chaos infrastructure and run an experiment end to end.
{% endhint %}

***

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

* **Idempotency check:** Confirm that duplicated requests do not cause double writes, double charges, or double messages.
* **Deduplication logic:** Validate the deduplication keys used by message-bus consumers actually work.
* **Protocol behavior:** Test that the receiver tolerates duplicate TCP segments without performance regression.
* **Observability:** Verify duplicate-request counts surface in metrics with the right tags.

***

### Before you begin <a href="#before-you-begin" id="before-you-begin"></a>

* **Chaos infrastructure:** A Linux chaos infrastructure (LCI) installed in one of the supported deployment models.
* **CF and BOSH credentials:** The LCI host has `CF_*`, `UAA_SERVER_ENDPOINT`, and `BOSH_*` credentials configured.
* **Target identifiers:** You know the `organization`, `space`, `app`, and the `boshDeployment`.
* **Network interface:** You know the interface name inside the container (typically `eth0`).
* **Destinations:** You know the host(s), IP range(s), or port(s) to affect.

***

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

| Platform                                                                  | Support status |
| ------------------------------------------------------------------------- | -------------- |
| Cloud Foundry (TAS, PCF, open-source) running on BOSH-managed Diego cells | Supported      |

***

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

| Action                                                              | Requirement                                                                                                                 |
| ------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------- |
| List apps the CF user can access                                    | `SpaceDeveloper`, `SpaceAuditor`, `OrgManager`, or `OrgAuditor`; scopes `cloud_controller.read` or `cloud_controller.admin` |
| List BOSH deployments                                               | BOSH user with `bosh.read` scope                                                                                            |
| SSH to a Diego cell via BOSH                                        | BOSH UAA token with `bosh.ssh` or `bosh.admin` scope                                                                        |
| Apply traffic-shaping rules inside the target container's namespace | Operator with `sudo` or root on the cell host                                                                               |

***

### Authentication <a href="#authentication" id="authentication"></a>

| Layer                                                | Where to provide                                         | Tunables                                                                                                                                        |
| ---------------------------------------------------- | -------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------- |
| Cloud Foundry API + BOSH director                    | `/etc/linux-chaos-infrastructure/cf.env` on the LCI host | `CF_API_ENDPOINT`, `CF_USERNAME`, `CF_PASSWORD`, `UAA_SERVER_ENDPOINT`, `BOSH_CLIENT`, `BOSH_CLIENT_SECRET`, `BOSH_CA_CERT`, `BOSH_ENVIRONMENT` |
| vSphere (only when `faultInjectorLocation: vSphere`) | `/etc/linux-chaos-infrastructure/vsphere.env`            | `GOVC_URL`, `GOVC_USERNAME`, `GOVC_PASSWORD`, `GOVC_INSECURE`, `VM_NAME`, `VM_USERNAME`, `VM_PASSWORD`                                          |

***

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

**Required parameters**

| Tunable           | Description                                         | Default    |
| ----------------- | --------------------------------------------------- | ---------- |
| `deploymentModel` | LCI placement model. One of `model-1` or `model-2`. | (required) |
| `organization`    | CF organization that owns the app.                  | (required) |
| `space`           | CF space within the organization.                   | (required) |
| `app`             | App whose egress traffic is duplicated.             | (required) |

**Chaos parameters**

| Tunable                       | Description                                                                    | Default |
| ----------------------------- | ------------------------------------------------------------------------------ | ------- |
| `packetDuplicationPercentage` | Percentage of egress packets to duplicate (0-100).                             | `100`   |
| `networkInterface`            | Network interface inside the container.                                        | `eth0`  |
| `destinationHosts`            | Comma-separated list of hostnames to affect. Leave empty to affect all egress. | `""`    |
| `destinationIPs`              | Comma-separated list of destination IPs or CIDRs to affect.                    | `""`    |
| `sourcePorts`                 | Comma-separated list of source ports to affect.                                | `""`    |
| `destinationPorts`            | Comma-separated list of destination ports to affect.                           | `""`    |
| `instanceAffectedPercentage`  | Percentage of instances to target. `0` targets exactly one.                    | `0`     |
| `boshDeployment`              | BOSH deployment name. Required for `deploymentModel: model-2`.                 | `""`    |
| `faultInjectorLocation`       | `local` or `vSphere`. Required for `deploymentModel: model-2`.                 | `local` |
| `faultInjectorPort`           | Local port used by the fault-injector.                                         | `50320` |
| `duration`                    | Total chaos duration.                                                          | `30s`   |
| `skipSSLValidation`           | Skip SSL validation when calling CF APIs.                                      | `false` |
| `rampTime`                    | Wait period in seconds before and after the fault.                             | `0`     |

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).

***

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

Authenticates to Cloud Foundry and BOSH, locates the target app instance(s), and installs a traffic-shaping rule on `networkInterface` inside the container's network namespace that duplicates `packetDuplicationPercentage`% of packets matching the configured destinations/ports. The rule is removed when `duration` elapses.

***

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

* The receiver's TCP stack discards duplicate segments cleanly; throughput on the wire rises.
* For UDP-based protocols, the receiver may observe duplicate datagrams at the application layer.
* After the fault ends, network behavior returns to baseline.

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

* **Application duplicate counts:** Confirm deduplication metrics catch the duplicates without amplification.
* **Throughput on the wire:** Observe inflated egress volume during the experiment.

***

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

* The traffic-shaping rule is removed at the end of `duration`.

***

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

* Operates on the egress side only.
* TCP-based traffic mostly absorbs duplication transparently; effects are most visible on UDP or application-layer protocols.

***

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

<details>

<summary>CF app network duplication: no observable effect in Harness Chaos Engineering</summary>

TCP-based traffic typically absorbs duplication transparently. To validate the fault is active, inspect outbound packet counters on the cell during the experiment; you should see roughly packetDuplicationPercentage% more egress packets.

</details>

***

### Common configurations <a href="#common-configurations" id="common-configurations"></a>

#### Duplicate UDP traffic to a metric collector <a href="#duplicate-udp-traffic-to-a-metric-collector" id="duplicate-udp-traffic-to-a-metric-collector"></a>

```yaml
apiVersion: litmuchaos.io/v1alpha1
kind: LinuxFault
metadata:
  name: cf-app-network-duplication
  labels:
    name: app-network-duplication
spec:
  cfAppNetworkChaos/inputs:
    duration: 60s
    deploymentModel: model-2
    faultInjectorLocation: vSphere
    app: cf-app
    organization: dev-org
    space: dev-space
    boshDeployment: cf
    networkInterface: eth0
    packetDuplicationPercentage: 50
    destinationIPs: 10.0.0.42
    destinationPorts: "8125"
```

***

The following Cloud Foundry secrets reside on the same machine where the chaos infrastructure is executed. These secrets are provided in the `/etc/linux-chaos-infrastructure/cf.env` file in the following format:

```env
CF_API_ENDPOINT=XXXXXXXXXXXXXXXXXXX
CF_USERNAME=XXXXXXXXXXXXXXXXXXXXXXX
CF_PASSWORD=XXXXXXXXXXXXXXXXXXXXXXX
UAA_SERVER_ENDPOINT=XXXXXXXXXXXXXXX
BOSH_CLIENT=XXXXXXXXXXXXXXXXXXXXXXX
BOSH_CLIENT_SECRET=XXXXXXXXXXXXXXXX
BOSH_CA_CERT=XXXXXXXXXXXXXXXXXXXXXX
BOSH_ENVIRONMENT=XXXXXXXXXXXXXXXXXX
```

{% hint style="info" %}
If the secrets file is not provided, the secrets are attempted to be derived from environment variables and the config file by the fault-injector.
{% endhint %}

| ENV name              | Description                                                   | Example                           |
| --------------------- | ------------------------------------------------------------- | --------------------------------- |
| CF\_API\_ENDPOINT     | API endpoint for the CF setup                                 | `https://api.system.cf-setup.com` |
| CF\_USERNAME          | Username for the CF user                                      | `username`                        |
| CF\_PASSWORD          | Password for the CF user                                      | `password`                        |
| UAA\_SERVER\_ENDPOINT | API endpoint for the UAA server for the CF setup              | `https://uaa.system.cf-setup.com` |
| BOSH\_CLIENT          | Used by the `bosh` CLI, the BOSH client                       | `admin`                           |
| BOSH\_CLIENT\_SECRET  | Used by the `bosh` CLI, the BOSH client secret                | `UBu9Fu3oW35sO6fw12auPH76gsRTy7`  |
| BOSH\_CA\_CERT        | Used by the `bosh` CLI, the file path for BOSH CA certificate | `/root/root_ca_certificate`       |
| BOSH\_ENVIRONMENT     | Used by the `bosh` CLI, the BOSH environment                  | `bosh.corp.local`                 |

## Fault injector ENVs and config file <a href="#fault-injector-envs-and-config-file" id="fault-injector-envs-and-config-file"></a>

If `/etc/linux-chaos-infrastructure/cf.env` file is not provided, fault-injector attempts to derive the secrets from environment variables or a configuration file. Any secret that is re-declared will be overridden in the following order of decreasing precedence:

1. `/etc/linux-chaos-infrastructure/cf.env` file
2. Environment variables
3. Configuration file

The configuration file should be provided at `/etc/linux-chaos-infrastructure/cf-fault-injector.yaml`:

```yaml
cf-api-endpoint: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
username: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
password: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
uaa-server-endpoint: XXXXXXXXXXXXXXXXXXXXXXXXXX
bosh-client: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
bosh-client-secret: XXXXXXXXXXXXXXXXXXXXXXXXXXX
bosh-ca-cert: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
bosh-environment: XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
```

A mapping between all the three formats for providing the secrets is as follows:

| cf.env                | ENV                   | cf-fault-injector.yaml |
| --------------------- | --------------------- | ---------------------- |
| CF\_API\_ENDPOINT     | CF\_API\_ENDPOINT     | cf-api-endpoint        |
| CF\_USERNAME          | USERNAME              | username               |
| CF\_PASSWORD          | PASSWORD              | password               |
| UAA\_SERVER\_ENDPOINT | UAA\_SERVER\_ENDPOINT | uaa-server-endpoint    |
| BOSH\_CLIENT          | BOSH\_CLIENT          | bosh-client            |
| BOSH\_CLIENT\_SECRET  | BOSH\_CLIENT\_SECRET  | bosh-client-secret     |
| BOSH\_CA\_CERT        | BOSH\_CA\_CERT        | bosh-ca-cert           |
| BOSH\_ENVIRONMENT     | BOSH\_ENVIRONMENT     | bosh-environment       |

These secrets are provided only if vSphere is used as the deployment platform for CF.

The following vSphere secrets reside on the same machine where the chaos infrastructure is executed. These secrets are provided in the `/etc/linux-chaos-infrastructure/vsphere.env` file in the following format:

```env
GOVC_URL=XXXXXXXXXXXXXXXXXXXXXX
GOVC_USERNAME=XXXXXXXXXXXXXXXXX
GOVC_PASSWORD=XXXXXXXXXXXXXXXXX
GOVC_INSECURE=XXXXXXXXXXXXXXXXX
VM_NAME=XXXXXXXXXXXXXXXXXXXXXXX
VM_USERNAME=XXXXXXXXXXXXXXXXXXX
VM_PASSWORD=XXXXXXXXXXXXXXXXXXX
```

| ENV Name       | Description                                                          | Notes                          |
| -------------- | -------------------------------------------------------------------- | ------------------------------ |
| GOVC\_URL      | Endpoint for vSphere                                                 | For example, `192.168.214.244` |
| GOVC\_USERNAME | Username for the vSphere user                                        | For example, `username`        |
| GOVC\_PASSWORD | Password for the vSphere user                                        | For example, `password`        |
| GOVC\_INSECURE | Skip SSL validation for govc commands                                | For example, `true`            |
| VM\_NAME       | Name of the vSphere VM where the fault-injector utility is installed | For example, `cf-vm`           |
| VM\_USERNAME   | Username for the VM guest user                                       | For example, `root`            |
| VM\_PASSWORD   | Password for the VM guest user                                       | For example, `password`        |

***

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

* [CF app network corruption](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/cloud-foundry/cf-app-network-corruption.md): Corrupt packets to test parser robustness.
* [CF app network loss](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/cloud-foundry/cf-app-network-loss.md): Drop packets to test retransmission and retry behavior.