Question

我在已部署到Heroku的应用程序中遇到了问题。当我在localhost上开发它时，没有收到此错误，但是一旦部署它，它就会自发地抛出此错误：

Access to fetch at 
'https://frontend.herokuapp.com' from origin 
'https://backend.herokuapp.com' has been blocked 
by CORS policy: No 'Access-Control-Allow-Origin' header is present 
on the requested resource. If an opaque response serves your needs, 
set the request's mode to 'no-cors' to fetch the resource with CORS 
disabled.

Flask服务器的简化版本：

from flask import Flask, request, make_response, jsonify, url_for, 
redirect, render_template
from flask_cors import CORS, cross_origin
import flask
import json

app = Flask(__name__)
CORS(app)

@app.route('/api/action', methods=['GET', 'POST'])
@cross_origin()
def prescription(response={}):

    # POST request
    if request.method == 'POST':
         print('score POST request')
         response = request.get_json()
         data = json.loads(response.get('data'))
         rating = a_super_cool_feature
         return jsonify(rating), 200

     # GET request
    else:
        print('GET request')
        return getScore(response)

@app.route('/api/score', methods=['GET', 'POST'])
@cross_origin()
def scoreHandler(response={}):

    # POST request
    if request.method == 'POST':
         print('Incoming..')
        response = request.get_json()
        parseResponse(response)
        return str(getScore(response)), 200


    # GET request
    else:
        return getScore(response)


@app.route('/test')
def test_page():
    # look inside `templates` and serve `index.html`
    return render_template('index.html')

if __name__ == "__main__":
     app.debug=True
     app.run()

我的前端是一个React应用程序。这两个服务器在单独的Heroku服务器上运行，并且我使用的是免费版本，因此一次只能获得一个dyno（以防可能导致此错误）。

有趣的是：

大约有一半的时间，在已部署的Heroku应用程序上调用这些POST请求时，将引发错误。否则，它没有问题。有解决此问题的想法吗？

Answer 1

您可以使用此代码段在cors应用程序范围内启用

。

def create_base_network():
    """
    Base network to be shared.
    """
    model_input = Input(shape=(224,224,3))

    x = Conv2D(64, (3, 3), activation='relu', padding='same')(model_input)
    x = MaxPooling2D(pool_size=(2,2))(x)
    x = Dropout(0.5)(x)

    x = BatchNormalization()(x)
    x = Conv2D(128, (3, 3), activation='relu', padding='same')(x)
    x = Conv2D(128, (3, 3), activation='relu', padding='same')(x)
    x = MaxPooling2D(pool_size=(2,2))(x)
    x = Dropout(0.5)(x)

    x = BatchNormalization()(x)
    x = Conv2D(256, (3, 3), activation='relu', padding='same')(x)
    x = Conv2D(256, (3, 3), activation='relu', padding='same')(x)
    x = MaxPooling2D(pool_size=(2,2))(x)
    x = Conv2D(256, (3, 3), activation='relu', padding='same')(x)
    x = Conv2D(256, (3, 3), activation='relu', padding='same')(x)
    x = MaxPooling2D(pool_size=(2,2))(x)
    x = Dropout(0.5)(x)

    x = BatchNormalization()(x)
    x = Conv2D(512, (3, 3), activation='relu', padding='same')(x)
    x = Conv2D(512, (3, 3), activation='relu', padding='same')(x)
    x = MaxPooling2D(pool_size=(2,2))(x)
    x = Conv2D(512, (3, 3), activation='relu', padding='same')(x)
    x = Conv2D(512, (3, 3), activation='relu', padding='same')(x)
    x = Conv2D(512, (3, 3), activation='relu', padding='same')(x)
    #x = MaxPooling2D(pool_size=(2,2))(x)
    x = Dropout(0.5)(x)

    #x = Flatten()(x)
    x = Dense(1024, activation='relu')(x)
    x = BatchNormalization()(x)
    x = Dropout(0.7)(x)

    x = Dense(1024, activation='relu')(x)
    x = Dense(1024, activation='relu')(x)
    x = BatchNormalization()(x)
    x = Dropout(0.7)(x)

    x = Dense(4096, activation='relu')(x)
    x = Dense(4096, activation='relu')(x)
    x = BatchNormalization()(x)
    x = Dropout(0.7)(x)
    # This layer is what the features are
    x = Dense(4096, activation='relu')(x)


    model = Model(inputs=model_input, outputs=x)
    return model

Answer 2

真的很奇怪的伪装修复。基本上，在向Flask后端发出POST请求时，大约有40％的时间会给我这个错误，然后我添加了

 app.config['CORS_HEADERS'] = 'Content-Type'

在以下位置：

app = Flask(__name__)
CORS(app)

这并不能完全解决问题。然而;现在，仅在向后端提出请求时，才抛出此错误的时间约为5％。请参阅其他答案以获取实际修复。

Answer 3

好的，现在我已经修复了它。我在Heroku中购买了“ Hobby”测功机，但现在我再也听不到错误。我认为这与我发出请求时另一台服务器无法正常运行有关，因为免费版本一次只能运行一个dyno。因此，它以某种方式超时并给出了该错误。

使用Hobby dyno类型，我的后端始终处于运行状态，因此当我发出请求时，它不再超时并给出该错误。

Flask API部署后出现Heroku“ CORS被阻止”错误

3 个答案: