【Azure 应用服务】App Service for Linux 中实现 WebSocket 功能 (Python SocketIO)

问题描述

使用 python websockets 模块作为Socket的服务端，发布到App Service for Linux环境后，发现Docker Container无法启动。错误消息为：

2021-10-28T02:39:51.812Z INFO  - docker run -d -p 1764:8000 --name test_0_c348bc62 -e WEBSITE_SITE_NAME=sockettest -e WEBSITE_AUTH_ENABLED=False -e WEBSITE_ROLE_INSTANCE_ID=0 -e WEBSITE_HOSTNAME=sockettest.chinacloudsites.cn -e WEBSITE_INSTANCE_ID=08307498aa991c84523184617d17f074bad5139bd2c0710fdf2b1a0ad3d3a9b7 -e HTTP_LOGGING_ENABLED=1 appsvc/python:3.8_20210709.2 python socket_server.py

2021-10-28T02:39:55.922Z INFO  - Initiating warmup request to container test_0_c348bc62 for site sockettest
2021-10-28T02:40:11.177Z INFO  - Waiting for response to warmup request for container test_0_c348bc62. Elapsed time = 15.2556084 sec
...
2021-10-28T02:43:33.439Z INFO  - Waiting for response to warmup request for container test_0_c348bc62. Elapsed time = 217.5175373 sec
2021-10-28T02:43:46.644Z ERROR - Container test_0_c348bc62 for site sockettest did not start within expected time limit. Elapsed time = 230.7221775 sec
2021-10-28T02:43:46.645Z ERROR - Container test_0_c348bc62 didn't respond to HTTP pings on port: 8000, failing site start. See container logs for debugging.
2021-10-28T02:43:46.672Z INFO  - Stopping site sockettest because it failed during startup.

PS:应用上云的需求。

问题解决

这是因为App Service Linux使用Container的启动需要Python代码中对HTTP进行正确的响应，否则Site无法启动。而这次的Python代码并不包含对HTTP请求的响应（需要Web框架），所以无法正确启动。

在Azure App Service for Linux - Python的文档中，主要介绍的两种Web框架为 Flask 和 Django。接下来，就通过Flask 和SocketIO来实现WebSocket功能。

实现 Python ad8 SocketIO 代码及步骤

1）创建 app.py 文件，并复制以下内容，作为Socket的服务端及Flask应用的启动

from flask import Flask, render_template, session, copy_current_request_context
from flask_socketio import SocketIO, emit, disconnect
from threading import Lock
import os

async_mode = None
app = Flask(__name__)

app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app, async_mode=async_mode)
thread = None
thread_lock = Lock()

## Used by App Service For linux
PORT = os.environ["PORT"]
serverIP = "0.0.0.0"

# # Used by Local debug.
# PORT = 5000
# serverIP = "127.0.0.1"

@app.route('/')
def index():
return render_template('index.html', async_mode=socketio.async_mode)

@socketio.on('my_event', namespace='/test')
def test_message(message):
print('receive message:' + message['data'],)
session['receive_count'] = session.get('receive_count', 0) + 1
emit('my_response',
{'data': message['data'], 'count': session['receive_count']})

@socketio.on('my_broadcast_event', namespace='/test')
def test_broadcast_message(message):
print('broadcast message:' + message['data'],)
session['receive_count'] = session.get('receive_count', 0) + 1
emit('my_response',
{'data': message['data'], 'count': session['receive_count']},
broadcast=True)

@socketio.on('disconnect_request', namespace='/test')
def disconnect_request():
@copy_current_request_context
def can_disconnect():
disconnect()

session['receive_count'] = session.get('receive_count', 0) + 1
emit('my_response',
{'data': 'Disconnected!', 'count': session['receive_count']},
callback=can_disconnect)

if __name__ == '__main__':
socketio.run(app,port=PORT, host=serverIP, debug=True)
print('socket io start')

2）创建 template/index.html，并复制以下内容，作为Socket的客户端，验证WebSocket的正常工作

<!DOCTYPE HTML>
<html>
<head>
<title>Socket-Test</title>
<script src="//code.jquery.com/jquery-1.12.4.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/socket.io/2.2.0/socket.io.js"></script>
<script type="text/javascript" charset="utf-8">
$(document).ready(function() {

namespace = '/test';
var socket = io(namespace);

socket.on('connect', function() {
socket.emit('my_event', {data: 'connected to the SocketServer...'});
});

socket.on('my_response', function(msg, cb) {
$('#log').append('<br>' + $('<div/>').text('logs #' + msg.count + ': ' + msg.data).html());
if (cb)
cb();
});
$('form#emit').submit(function(event) {
socket.emit('my_event', {data: $('#emit_data').val()});
return false;
});
$('form#broadcast').submit(function(event) {
socket.emit('my_broadcast_event', {data: $('#broadcast_data').val()});
return false;
});
$('form#disconnect').submit(function(event) {
socket.emit('disconnect_request');
return false;
});
});
</script>
</head>
<body style="background-color:white;">

<h1 style="background-color:white;">Socket</h1>
<form id="emit" method="POST" action='#'>
<input type="text" name="emit_data" id="emit_data" placeholder="Message">
<input type<
ad8
span style="color: rgba(0, 0, 255, 1)">="submit" value="Send Message">
</form>
<form id="broadcast" method="POST" action='#'>
<input type="text" name="broadcast_data" id="broadcast_data" placeholder="Message">
<input type="submit" value="Send Broadcast Message">
</form>

<form id="disconnect" method="POST" action="#">
<input type="submit" val
ad8
ue="Disconnect Server">
</form>
<h2 style="background-color:white;">Logs</h2>
<div id="log" ></div>
</body>
</html>

3）创建 requirements.txt 文件，并包含以下module及版本，如果版本不适合，可以适当修改。

Flask==1.0.2
Flask-Login==0.4.1
Flask-Session==0.3.1
itsdangerous==1.1.0
Jinja2==2.10
MarkupSafe==1.1.0
six==1.11.0
Werkzeug==0.14.1
Flask-SocketIO==4.3.1
python-engineio==3.13.2
python-socketio==4.6.0
eventlet==0.30.2

以上三个就是整个项目的源文件，VS Code中的文件结构为：

4）在VS Code中使用az webapp up来部署Python Web应用

#设置登录环境为中国区Azure
az cloud set -n AzureChinaCloud
az login

#部署代码，如果pythonlinuxwebsocket01不存在，则自动创建定价层位B1的App Service
az webapp up --sku B1 --name pythonlinuxwebsocket01

效果展示：

5）修改App Service的启动命令

gunicorn --worker-class eventlet -w 1 app:app

注：为了避免 flask-socketIO 服务器部署 400 Bad Request 问题，所以需要使用 eventlet 作为工作进程。详细说明可见：https://blog.csdn.net/weixin_43958804/article/details/109024348

6) 开启WebSocket，启用HTTP, 设置PORT参数

注：修改后，重启App Service。如果重启后使用HTTP请求，但是发生了302跳转到HTTPS的情况，就可以考虑重新部署一次站点。使用第四步方法，az webapp up然container重新生成项目信息。

7）验证Web Socket

使用HTTP访问刚刚部署的App Service URL。

附录一：解决flask-socketIO 服务器部署 400 Bad Request 问题

使用eventlet，设置启动命令：gunicorn --worker-class eventlet -w 1 app:app

附录二：Gunicorn ImportError: cannot import name 'ALREADY_HANDLED' from 'eventlet.wsgi' in docker

Installing older version of eventlet solved the problem:

pip install eventlet==0.30.2

参考资料：

Implement a WebSocket Using Flask and Socket-IO(Python)： https://medium.com/swlh/implement-a-websocket-using-flask-and-socket-io-python-76afa5bbeae1

解决flask-socketIO 服务器部署 400 Bad Request 问题：https://blog.csdn.net/weixin_43958804/article/details/109024348