在Google Colab中创建Flask应用遇连接拒绝错误，如何解决？

我正在Google Colab笔记本中基于sklearn pipeline开发机器学习模型，并尝试将其部署。使用了以下代码：

import tensorflow_datasets as tfds
import tensorflow as tf
from flask import Flask, jsonify, make_response, request
from flask_ngrok import run_with_ngrok

app = Flask(__name__)
run_with_ngrok(app)

padding_size = 1000
model = pipeline

print('Model and Vocabalory loaded.......')

@app.route("/")
def hello():
    return "I am alive!"

if __name__ == '__main__':
    app.run()

运行后遇到如下错误：

Model and Vocabalory loaded.......

Serving Flask app 'main'

Debug mode: off INFO:werkzeug:WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.

Running on http://127.0.0.1:5000 INFO:werkzeug:Press CTRL+C to quit Exception in thread Thread-17: Traceback (most recent call last): File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 203, in _new_conn sock = connection.create_connection( File "/usr/local/lib/python3.10/dist-packages/urllib3/util/connection.py", line 85, in create_connection raise err File "/usr/local/lib/python3.10/dist-packages/urllib3/util/connection.py", line 73, in create_connection sock.connect(sa) ConnectionRefusedError: [Errno 111] Connection refused

The above exception was the direct cause of the following exception:

Traceback (most recent call last): File "/usr/local/lib/python3.10/dist-packages/urllib3/connectionpool.py", line 791, in urlopen response = self._make_request( File "/usr/local/lib/python3.10/dist-packages/urllib3/connectionpool.py", line 497, in _make_request conn.request( File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 395, in request self.endheaders() File "/usr/lib/python3.10/http/client.py", line 1278, in endheaders self._send_output(message_body, encode_chunked=encode_chunked) File "/usr/lib/python3.10/http/client.py", line 1038, in _send_output self.send(msg) File "/usr/lib/python3.10/http/client.py", line 976, in send self.connect() File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 243, in connect self.sock = self._new_conn() File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 218, in _new_conn raise NewConnectionError( urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPConnection object at 0x79d8a4408b80>: Failed to establish a new connection: [Errno 111] Connection refused

The above exception was the direct cause of the following exception:

Traceback (most recent call last): File "/usr/local/lib/python3.10/dist-packages/requests/adapters.py", line 486, in send resp = conn.urlopen( File "/usr/local/lib/python3.10/dist-packages/urllib3/connectionpool.py", line 845, in urlopen retries = retries.increment( File "/usr/local/lib/python3.10/dist-packages/urllib3/util/retry.py", line 515, in increment raise MaxRetryError(_pool, url, reason) from reason  # type: ignore[arg-type] urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='localhost', port=4040): Max retries exceeded with url: /api/tunnels (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x79d8a4408b80>: Failed to establish a new connection: [Errno 111] Connection refused'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last): File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner self.run() File "/usr/lib/python3.10/threading.py", line 1378, in run self.function(*self.args, **self.kwargs) File "/usr/local/lib/python3.10/dist-packages/flask_ngrok.py", line 70, in start_ngrok ngrok_address = _run_ngrok() File "/usr/local/lib/python3.10/dist-packages/flask_ngrok.py", line 35, in _run_ngrok tunnel_url = requests.get(localhost_url).text  # Get the tunnel information File "/usr/local/lib/python3.10/dist-packages/requests/api.py", line 73, in get return request("get", url, params=params, **kwargs) File "/usr/local/lib/python3.10/dist-packages/requests/api.py", line 59, in request return session.request(method=method, url=url, **kwargs) File "/usr/local/lib/python3.10/dist-packages/requests/sessions.py", line 589, in request resp = self.send(prep, **send_kwargs) File "/usr/local/lib/python3.10/dist-packages/requests/sessions.py", line 703, in send r = adapter.send(request, **kwargs) File "/usr/local/lib/python3.10/dist-packages/requests/adapters.py", line 519, in send raise ConnectionError(e, request=request) requests.exceptions.ConnectionError: HTTPConnectionPool(host='localhost', port=4040): Max retries exceeded with url: /api/tunnels (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x79d8a4408b80>: Failed to establish a new connection: [Errno 111] Connection refused'))

解决方法 #

1. 确保Ngrok正确安装并配置Auth Token

flask_ngrok依赖Ngrok服务，但Colab环境默认没有正确初始化Ngrok，需要手动完成以下步骤：

• 安装flask-ngrok（如果未安装）：

  !pip install flask-ngrok
  

• 下载并解压Ngrok二进制文件：

  !wget https://bin.equinox.io/c/bNyj1mQVY4c/ngrok-v3-stable-linux-amd64.tgz
  !tar -xvzf ngrok-v3-stable-linux-amd64.tgz
  

• 设置Ngrok Auth Token（需从Ngrok官网获取免费token）：

  !./ngrok config add-authtoken YOUR_AUTH_TOKEN
  

2. 改用Pyngrok替代Flask-Ngrok（更稳定）

pyngrok是官方维护的Ngrok Python库，兼容性更好，步骤如下：

• 安装pyngrok：

  !pip install pyngrok
  

• 修改部署代码：

  from flask import Flask, jsonify, make_response, request
  from pyngrok import ngrok
  
  app = Flask(__name__)
  
  # 启动Ngrok隧道，指向Flask默认的5000端口
  public_url = ngrok.connect(5000).public_url
  print(f"可访问的公网URL: {public_url}")
  
  padding_size = 1000
  model = pipeline  # 确保此处的pipeline已完成训练和加载
  
  print('Model and Vocabulary loaded.......')
  
  @app.route("/")
  def hello():
      return "I am alive!"
  
  if __name__ == '__main__':
      app.run()
  

3. 检查端口占用（可选）

如果仍有问题，检查5000端口是否被占用：

!lsof -i :5000

若有占用进程，可通过kill命令终止，但Colab环境中这种情况极少出现。

内容的提问来源于stack exchange，提问作者Shalini Raghuram