問題描述

在成功的部署Python flask應用到App Service (Windows)後，如果需要把當前專案（如：hiflask）作為一個子專案(子站點），把web.config檔案從wwwroot中移動到專案資料夾中。訪問時，確遇見了404 Not Found的錯誤。

檢視flask專案的啟動日誌，可以看見專案啟動已經成功。但是為什麼請求一直都是404的問題呢？

2021-09-10 05:29:58.224796: wfastcgi.py will restart when files in D:\home\site\wwwroot\hiflask\ are changed: .*((\.py)|(\.config))$

2021-09-10 05:29:58.240445: wfastcgi.py 3.0.0 initialized

問題解決

在搜尋 flask return 404問題後，發現是因為 URL字首（prefixed ）的問題。因為當前的flask應用訪問路徑不再是根目錄（/），而是(/hiflask)。 所以需要 flask專案中使用 中介軟體 來處理 url字首的問題。

原文內容為：https://stackoverflow.com/questions/18967441/add-a-prefix-to-all-flask-routes/36033627#36033627

ll you have to do is to write a middleware to make the following changes:

  1. modify PATH_INFO to handle the prefixed url.
  2. modify SCRIPT_NAME to generate the prefixed url.

Like this:

class PrefixMiddleware(object):

    def __init__(self, app, prefix=''):

        self.app = app

        self.prefix = prefix

    def __call__(self, environ, start_response):

        if environ['PATH_INFO'].startswith(self.prefix):

            environ['PATH_INFO'] = environ['PATH_INFO'][len(self.prefix):]

            environ['SCRIPT_NAME'] = self.prefix

            return self.app(environ, start_response)

        else:

            start_response('404', [('Content-Type', 'text/plain')])

            return ["This url does not belong to the app.".encode()]

Wrap your app with the middleware, like this:

from flask import Flask, url_for

app = Flask(__name__)

app.debug = True

app.wsgi_app = PrefixMiddleware(app.wsgi_app, prefix='/foo')

@app.route('/bar')

def bar():

    return "The URL for this page is {}".format(url_for('bar'))

if __name__ == '__main__':

    app.run('0.0.0.0', 9010)

Visit http://localhost:9010/foo/bar,

You will get the right result: The URL for this page is /foo/bar

而在App Service中的解決方式就是添加了 PrefixMiddleware，並指定prefix為 /hiflask 。 附上完成的hiflask/app.py 程式碼和web.config內容。

hiflask/app.py

from flask import Flask

from datetime import datetime

from flask import render_template

import re

class PrefixMiddleware(object):

    def __init__(self, app, prefix=''):

        self.app = app

        self.prefix = prefix

    def __call__(self, environ, start_response):

        if environ['PATH_INFO'].startswith(self.prefix):

            environ['PATH_INFO'] = environ['PATH_INFO'][len(self.prefix):]

            environ['SCRIPT_NAME'] = self.prefix

            return self.app(environ, start_response)

        else:

            start_response('404', [('Content-Type', 'text/plain')])

            return ["This url does not belong to the app.".encode()]

#if __name__ =="__name__"

app = Flask(__name__)

app.debug = True

app.wsgi_app = PrefixMiddleware(app.wsgi_app, prefix='/hiflask')

# @app.route("/")

# def home():

#     return "Hello, Flask!"

print("flask applicaiton started and running..." +datetime.now().strftime("%m/%d/%Y, %H:%M:%S"))

# Replace the existing home function with the one below

@app.route("/")

def home():

    return render_template("home.html")

# New functions

@app.route("/about/")

def about():

    return render_template("about.html")

@app.route("/contact/")

def contact():

    return render_template("contact.html")

@app.route("/hello/")

@app.route("/hello/<name>")

def hello_there(name = None):

    return render_template(

        "hello_there.html",

        name=name,

        date=datetime.now()

    )

@app.route("/api/data")

def get_data():

    return app.send_static_file("data.json")

if __name__ == '__main__':

    app.run(debug=True)

hiflask/web.config

<?xml version="1.0" encoding="utf-8"?>

<configuration>

  <appSettings>

    <add key="WSGI_HANDLER" value="app.app"/>

    <add key="PYTHONPATH" value="D:\home\site\wwwroot\hiflask"/>

    <add key="WSGI_LOG" value="D:\home\site\wwwroot\hiflask\hiflasklogs.log"/>

  </appSettings>

  <system.webServer>

    <handlers>

    <add name="PythonHandler" path="*" verb="*" modules="FastCgiModule" scriptProcessor="D:\home\python364x64\python.exe|D:\home\python364x64\wfastcgi.py" resourceType="Unspecified" requireAccess="Script"/>

    </handlers>

  </system.webServer>

</configuration>

最終效果(作為子專案部署完成成功，所以一個app service就可以部署多個站點)

提醒一點：App Service中如果要部署多站點，需要在Configration 中配置 Virtual Applications。

參考資料：

https://stackoverflow.com/questions/18967441/add-a-prefix-to-all-flask-routes/36033627#36033627

https://www.cnblogs.com/lulight/p/15220297.html

https://www.cnblogs.com/lulight/p/15227028.html