Hey there! That tunnel error is super common lately because ngrok changed their requirements for free users. Let's walk through the fixes step by step:

1. The #1 Fix: Add Your ngrok Auth Token #

ngrok now requires a free account and auth token to create tunnels—older tutorials probably didn't mention this because it wasn't needed before. Here's how to set it up:

• Head to the ngrok website, sign up for a free account, and grab your unique Auth Token from the dashboard.
• In your Colab notebook, add this line before running your Flask code:

  !ngrok config add-authtoken YOUR_AUTH_TOKEN_HERE
  

  Replace YOUR_AUTH_TOKEN_HERE with the token you copied.

2. Update or Replace flask-ngrok #

The flask-ngrok library isn't actively maintained anymore, which can cause compatibility issues with newer Colab or ngrok versions. Try this more reliable alternative using pyngrok:

• First, uninstall the old package and install pyngrok:

  !pip uninstall flask-ngrok -y
  !pip install pyngrok
  

• Then use this updated code instead of your original:

  from flask import Flask
  from pyngrok import ngrok
  
  # Set your ngrok auth token
  ngrok.set_auth_token("YOUR_AUTH_TOKEN_HERE")
  
  app = Flask(__name__)
  
  @app.route("/")
  def hello_world():
      return 'Hello, World!'
  
  # Run Flask in a background thread so we can start ngrok
  import threading
  threading.Thread(target=app.run, kwargs={"use_reloader": False}).start()
  
  # Create the ngrok tunnel
  public_url = ngrok.connect(5000)
  print(f"Access your app here: {public_url}")
  

3. Check for Port Conflicts #

If the above fixes don't work, try using a different port (sometimes Colab has other processes using port 5000):

• Change app.run(port=5000) to app.run(port=5001)
• Update the ngrok connect line to ngrok.connect(5001)

Give these steps a shot—most folks fix the tunnel error by adding the auth token first. Let me know if you run into any other issues!

内容的提问来源于stack exchange，提问作者Olive Yew