> 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/aws/ec2-http-reset-peer.md).

# EC2 HTTP reset peer

EC2 HTTP reset peer is an AWS chaos fault that resets inbound TCP connections to an HTTP service on a specified port of a target EC2 instance for a configurable duration. The fault interposes a transparent HTTP proxy on the instance, scoped to `TARGET_SERVICE_PORT` and `NETWORK_INTERFACE`, and dispatches the proxy via AWS Systems Manager Run Command. The proxy answers incoming requests by sending a TCP RST instead of an HTTP response, simulating an unclean peer reset.

Use this fault to test how clients react when the server tears down connections mid-flight: do they retry safely, do they distinguish a reset from a clean failure, do they tear down keep-alive pools cleanly, does the load balancer detach the misbehaving instance?

{% 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:

* **Client retry safety:** When a connection is reset before the response arrives, does the client retry only idempotent requests, or does it retry POSTs and risk duplicate side effects?
* **Connection-pool churn:** Does the client's HTTP pool recover after every connection in it is reset within seconds?
* **Load-balancer behaviour:** Does the LB detach the instance because of failed health-check responses?
* **Observability:** Do TCP-level metrics (`tcp_reset_received`) and HTTP-level metrics (5xx rate) both show the failure?
* **Upstream propagation:** Does the reset surface to the end user as a clean error, or does it cause a cryptic upstream-level message?

***

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

* **Kubernetes version:** 1.21 or later for the chaos infrastructure cluster.
* **Target instance is reachable via SSM:** The instance has the SSM Agent running and an instance profile with `AmazonSSMManagedInstanceCore`.
* **Selector provided:** Either `EC2_INSTANCE_ID` or `EC2_INSTANCE_TAG` is set.
* **HTTP service runs on TARGET\_SERVICE\_PORT:** A plaintext HTTP service is listening on `TARGET_SERVICE_PORT`.
* **AWS credentials available:** Either an AWS credentials file uploaded as a **File Secret in Harness Secret Manager** (see Authentication below) or IRSA on the chaos infrastructure service account.

***

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

| Platform                                    | Support status                                           |
| ------------------------------------------- | -------------------------------------------------------- |
| Amazon EC2 (Linux instances with SSM Agent) | Supported                                                |
| Amazon EKS managed worker nodes             | Supported (if SSM Agent is installed)                    |
| Amazon EKS self-managed worker nodes        | Supported (if SSM Agent is installed)                    |
| Targeting by tag                            | Supported via `EC2_INSTANCE_TAG`                         |
| Targeting by ID                             | Supported via `EC2_INSTANCE_ID`                          |
| HTTPS traffic (TLS-encrypted)               | Not supported on the target port; terminate TLS upstream |
| Windows instances                           | Not supported (Linux-only proxy)                         |

***

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

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "ec2:DescribeInstances",
        "ec2:DescribeInstanceStatus"
      ],
      "Resource": "*"
    },
    {
      "Effect": "Allow",
      "Action": [
        "ssm:SendCommand",
        "ssm:CancelCommand",
        "ssm:GetCommandInvocation",
        "ssm:DescribeInstanceInformation",
        "ssm:GetDocument",
        "ssm:DescribeDocument"
      ],
      "Resource": "*"
    }
  ]
}
```

Go to [common policy for all AWS faults](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/security-configurations/policy-for-all-aws-faults.md) to use a single superset IAM policy.

***

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

The fault supports three credential delivery models. Pick one based on how your chaos infrastructure is deployed.

| Method                                | When to use it                                                                 | How to configure                                                                                                                                                                                                                    |
| ------------------------------------- | ------------------------------------------------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Harness Secret Manager file secret    | Chaos infrastructure runs outside EKS, or you want explicit static credentials | Upload the AWS credentials file as a **File Secret** in Harness Secret Manager and reference its identifier via `AWS_AUTHENTICATION_SECRET`                                                                                         |
| IAM Roles for Service Accounts (IRSA) | Chaos infrastructure runs in EKS and uses an OIDC-bound service account        | No tunable changes; the chaos pod inherits the role automatically. Go to [AWS IAM integration](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/security-configurations/aws-iam-integration.md) to set it up |
| Assume role                           | The fault needs to act in a different account or with elevated permissions     | Set `ASSUME_ROLE_ARN` to the role ARN; the chaos pod assumes the role on top of its base credentials                                                                                                                                |

When using the Harness Secret Manager method, the File Secret should contain an AWS credentials file in the standard `~/.aws/credentials` format:

```ini
[default]
aws_access_key_id = REPLACE_WITH_ACCESS_KEY_ID
aws_secret_access_key = REPLACE_WITH_SECRET_ACCESS_KEY
```

Upload this file as a **File Secret** in Harness Secret Manager (Project Setup → Secrets → New File Secret), and pass the secret identifier in `AWS_AUTHENTICATION_SECRET`.

***

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

**Required parameters**

| Tunable                                   | Description                                                | Default    |
| ----------------------------------------- | ---------------------------------------------------------- | ---------- |
| `REGION`                                  | AWS region that hosts the target instance.                 | (required) |
| `EC2_INSTANCE_ID` *or* `EC2_INSTANCE_TAG` | One of these must be set to select the target instance(s). | `""`       |
| `TARGET_SERVICE_PORT`                     | Port the target HTTP service listens on.                   | `80`       |

**Chaos parameters**

| Tunable                  | Description                                                                                          | Default    |
| ------------------------ | ---------------------------------------------------------------------------------------------------- | ---------- |
| `NETWORK_INTERFACE`      | Network interface where the HTTP proxy intercepts traffic.                                           | `eth0`     |
| `TOTAL_CHAOS_DURATION`   | Duration of the fault in seconds.                                                                    | `30`       |
| `INSTANCE_AFFECTED_PERC` | Percentage of matching instances to target (only with `EC2_INSTANCE_TAG`). `0` targets one instance. | `0`        |
| `INSTALL_DEPENDENCIES`   | Install the in-instance HTTP proxy if missing. Set to `False` to skip.                               | `True`     |
| `PROXY`                  | HTTP/HTTPS proxy used by the in-instance installer.                                                  | `""`       |
| `SEQUENCE`               | Order in which multiple instances are processed: `parallel` or `serial`.                             | `parallel` |
| `RAMP_TIME`              | Wait period in seconds before and after the fault.                                                   | `0`        |

**Authentication**

| Tunable                     | Description                                                                                                                       | Default |
| --------------------------- | --------------------------------------------------------------------------------------------------------------------------------- | ------- |
| `ASSUME_ROLE_ARN`           | ARN of an IAM role to assume on top of the base credentials.                                                                      | `""`    |
| `AWS_AUTHENTICATION_SECRET` | Identifier of the **File Secret in Harness Secret Manager** that contains the AWS credentials file. Not required when using IRSA. | `""`    |

***

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

Sends an SSM Run Command to the selected instance(s) in `REGION` that interposes an HTTP proxy on `NETWORK_INTERFACE` for traffic destined to `TARGET_SERVICE_PORT`; the proxy aborts every incoming connection by sending a TCP RST instead of an HTTP response for `TOTAL_CHAOS_DURATION` seconds before being removed.

***

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

* Every new TCP connection to `TARGET_SERVICE_PORT` is reset; clients see "connection reset by peer".
* Long-lived connections established before the fault are torn down by the next request that traverses the proxy.
* Clients that retry blindly may pile additional load on the instance during the fault.
* Load-balancer health checks against the port typically fail; the LB detaches the instance until checks recover.

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

The chaos pod removes the HTTP proxy and redirection rules. New connections succeed normally. Client-side connection pools should reconnect on the next request; some pool implementations need an explicit refresh.
{% endhint %}

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

* **Client connection-reset rate:** Use a Prometheus probe on the client's `tcp_connection_reset` or HTTP `5xx` counter.
* **Load-balancer target health:** Use a Prometheus probe on `aws_applicationelb_unhealthy_host_count`.
* **Application logs:** Use a [command probe](/resilience-testing/chaos-testing/probes/command-probe.md) that tails the application log via SSM and matches on `connection reset` or `EOF`.

***

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

While the experiment is running:

1. **Issue a request and observe the reset.**

   ```bash
   aws ssm send-command \
     --region <region> \
     --instance-ids <id> \
     --document-name AWS-RunShellScript \
     --parameters 'commands=["curl -v http://localhost:<TARGET_SERVICE_PORT>/ 2>&1 | tail -10"]'
   ```

   The output should show `Connection reset by peer` or similar.

***

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

* **End of duration:** The chaos pod stops the HTTP proxy and removes the redirection rules.
* **Abort the experiment:** Stopping the experiment from Chaos Studio cancels the in-flight SSM command and runs cleanup.
* **Manual cleanup:** If the proxy is left running, kill it via SSM Session Manager and remove any installed iptables rules.

***

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

* **HTTP only (no HTTPS):** The proxy operates on plaintext HTTP. Move TLS termination upstream before using this fault.
* **Linux-only payload:** This fault runs on Linux instances.
* **SSM Agent required:** Instances without the SSM Agent online cannot be targeted.
* **All connections affected:** Every connection to the port is reset; there is no per-URL or per-percentage filter.
* **Client-side pool recovery:** Some HTTP clients keep using a poisoned connection pool until they receive a fresh address. After the fault, force-refresh the pool from the client if needed.

***

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

<details>

<summary>EC2 HTTP reset peer experiment fails with InvalidInstanceId in Harness Chaos Engineering</summary>

The SSM Agent is not online for the target instance. Confirm with aws ssm describe-instance-information --filters 'Key=InstanceIds,Values='. If missing, install the SSM Agent and attach an instance profile that includes AmazonSSMManagedInstanceCore.

</details>

<details>

<summary>EC2 HTTP reset peer runs but connections still complete normally</summary>

The most common causes are: TARGET\_SERVICE\_PORT does not host an HTTP server (the proxy cannot interpose); the client connects via a different interface than NETWORK\_INTERFACE; TLS terminates at the port (HTTPS is not supported); or the in-instance proxy failed to install (set INSTALL\_DEPENDENCIES=True). Verify with 'curl -v <http://localhost:/>' via SSM during the fault.

</details>

<details>

<summary>EC2 HTTP reset peer left orphan iptables rules after the experiment</summary>

The fault was killed before cleanup ran. Connect via SSM Session Manager and remove the rules: iptables -t nat -L | grep , then iptables -t nat -D PREROUTING . Kill the orphan proxy with pkill -f .

</details>

***

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

* [EC2 HTTP latency](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/ec2-http-latency.md): Delay responses instead of resetting connections.
* [EC2 HTTP status code](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/ec2-http-status-code.md): Return a specific status code instead of resetting.
* [EC2 HTTP modify body](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/ec2-http-modify-body.md): Rewrite the response body.
* [EC2 HTTP modify header](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/ec2-http-modify-header.md): Rewrite request or response headers.
* [Common AWS fault tunables](/resilience-testing/chaos-engineering/faults/chaos-fault-categories/aws/aws-fault-tunables.md): Shared environment variables for AWS faults.