在Colab中使用flask_ngrok出现ConnectionRefusedError错误求助

我尝试在Google Colab中运行Flask应用，使用的代码如下：

from flask import Flask
!pip install flask_ngrok
from flask_ngrok import run_with_ngrok

app = Flask(__name__)
run_with_ngrok(app) 

@app.route("/")
def hello():
    return "Hello World!"

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

该代码来自官方示例文档（注：示例笔记本本身存在其他模块错误），但运行后持续出现以下错误：

Exception in thread Thread-11:
Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 174, in _new_conn
    conn = connection.create_connection(
  File "/usr/local/lib/python3.10/dist-packages/urllib3/util/connection.py", line 95, in create_connection
    raise err
  File "/usr/local/lib/python3.10/dist-packages/urllib3/util/connection.py", line 85, in create_connection
    sock.connect(sa)
ConnectionRefusedError: [Errno 111] Connection refused

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/urllib3/connectionpool.py", line 703, in urlopen
    httplib_response = self._make_request(
  File "/usr/local/lib/python3.10/dist-packages/urllib3/connectionpool.py", line 398, in _make_request
    conn.request(method, url, **httplib_request_kw)
  File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 244, in request
    super(HTTPConnection, self).request(method, url, body=body, headers=headers)
  File "/usr/lib/python3.10/http/client.py", line 1283, in request
    self._send_request(method, url, body, headers, encode_chunked)
  File "/usr/lib/python3.10/http/client.py", line 1329, in _send_request
    self.endheaders(body, encode_chunked=encode_chunked)
  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 205, in connect
    conn = self._new_conn()
  File "/usr/local/lib/python3.10/dist-packages/urllib3/connection.py", line 186, in _new_conn
    raise NewConnectionError(
urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPConnection object at 0x7f0594e70ca0>: 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/local/lib/python3.10/dist-packages/requests/adapters.py", line 440, in send
    resp = conn.urlopen(
  File "/usr/local/lib/python3.10/dist-packages/urllib3/connectionpool.py", line 787, in urlopen
    retries = retries.increment(
  File "/usr/local/lib/python3.10/dist-packages/urllib3/util/retry.py", line 592, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='localhost', port=4040): Max retries exceeded with url: /api/tunnels (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f0594e70ca0>: 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 75, in get
    return request('get', url, params=params, **kwargs)
  File "/usr/local/lib/python3.10/dist-packages/requests/api.py", line 61, in request
    return session.request(method=method, url=url, **kwargs)
  File "/usr/local/lib/python3.10/dist-packages/requests/sessions.py", line 529, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/local/lib/python3.10/dist-packages/requests/sessions.py", line 645, 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 0x7f0594e70ca0>: Failed to establish a new connection: [Errno 111] Connection refused'))

按照教程操作但每次都出这个错，无法获取ngrok公网链接，问题出在哪里？

问题原因及解决办法 #

核心原因 #

错误指向无法连接localhost:4040——这是flask-ngrok默认获取ngrok隧道信息的端口，本质是ngrok未成功启动，具体诱因包括：

• 旧版flask-ngrok依赖的ngrok版本已不兼容Colab最新环境，无法自动下载或运行ngrok二进制文件；
• ngrok v2及以上版本强制要求使用认证令牌才能创建隧道，旧版flask-ngrok未处理该逻辑，导致启动失败；
• Colab网络策略拦截了未认证的ngrok请求，无法建立隧道连接。

解决步骤 #

方法1：升级并配置ngrok认证令牌（推荐）

1. 注册ngrok账号，获取个人认证令牌（在ngrok控制台的"Your Authtoken"页面）；
2. 在Colab中运行以下代码：

!pip install flask pyngrok --upgrade
from flask import Flask
from pyngrok import ngrok, conf

# 替换为你的ngrok认证令牌
conf.get_default().auth_token = "你的ngrok认证令牌"

app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

# 启动ngrok隧道，映射Flask默认端口5000
public_url = ngrok.connect(5000).public_url
print(f"Flask应用公网链接：{public_url}")

app.run()

方法2：手动安装ngrok

若自动安装失败，手动下载并配置ngrok：

!wget https://bin.equinox.io/c/bNyj1mQVY4c/ngrok-v3-stable-linux-amd64.tgz
!tar -xvzf ngrok-v3-stable-linux-amd64.tgz
!./ngrok config add-authtoken 你的ngrok认证令牌

之后再运行方法1中的Flask+pyngrok代码即可。

方法3：使用Colab自带本地隧道（无需ngrok）

如果不想依赖ngrok，可使用Colab原生工具：

!pip install flask portpicker
from flask import Flask
import portpicker
from google.colab.output import serve_kernel_port_as_http

app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

port = portpicker.pick_unused_port()
serve_kernel_port_as_http(port)
print(f"访问链接：http://localhost:{port}")

app.run(port=port)

内容的提问来源于stack exchange，提问作者DDDyylan