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Message

Traffic was successfully tunneled to the ngrok agent, but the agent failed to establish a connection to the upstream web service at ADDR.

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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.

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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.
    • Confirm you can access it directly (e.g., 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.

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General Troubleshooting Steps

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

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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
  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

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Further help

If you’re having trouble resolving this error, please reach out to support@ngrok.com