> ## Documentation Index
> Fetch the complete documentation index at: https://ngrok.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Error 8012

## ERR\_NGROK\_8012

Traffic successfully made it to the ngrok agent, but the agent failed to establish a connection to the upstream web service at `ADDR`.

### Overview

This error occurs when the ngrok agent successfully receives traffic but fails to establish a connection with your local service (the "upstream" service). While the tunnel is created successfully, ngrok cannot forward the traffic to your application. This can happen with a Agent Endpoint or when using a Cloud Endpoint that forwards traffic to an agent.

### Common Issues and Solutions

1. **Local Service Not Running or Inaccessible**

   **Cause:** The web service or application on your local machine is not active or cannot be reached.

   **Resolution:**

   * Start your local service. If you don't have a local service to try with
     ngrok, see our [quickstart](/getting-started#3-start-your-app-or-service),
     for minimal apps in JavaScript, Go, and Python that work on port `8080`.
     * Confirm you can access it directly (for example, `http://localhost:8080`).
   * Restart ngrok with the correct port number.

2. **Incorrect Port Specified**

   **Cause:** The port in your ngrok command doesn't match your local service's port.

   **Resolution:**

   * Verify the port your local service is using.
   * Update your ngrok command to use the correct port.
   * Example: Use `ngrok http 3000` if your service runs on port 3000.

### General Troubleshooting Steps

1. Verify local service accessibility without ngrok.
2. Ensure the latest ngrok version is installed.
3. Restart the ngrok agent.

### Preventing Downtime

1. Use a Cloud Endpoint with a Traffic Policy to provide a better user experience. Instead of showing an error, you can detect the connection failure and serve a custom maintenance page. [Learn more about Cloud Endpoints and Traffic Policy](/gateway/cloud-endpoints/)

2. Use Endpoint Pooling to achieve high availability. By load balancing across multiple agents, traffic is automatically routed away from any agent experiencing this error, preventing any impact on your users. [Learn more about Endpoint Pooling](/gateway/endpoint-pooling/)

## Further help

If you're having trouble resolving this error, please reach out to [support@ngrok.com](mailto:support@ngrok.com?subject=Help%20with%20ERR_NGROK_8012)