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 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="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" value="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
