CORS配置节点.js到Python后端

Question

我有一个节点后端，当调用它时，需要向Python后端发出单独的请求，以进行图像分类预测。在本地运行这两个服务器时，调用可以完美地工作，但在托管时抛出503错误。你知道吗

节点服务器接收一个多部分/表单数据映像，然后将其重新发送到Python服务器。同样，整个路由调用在本地工作。我还用Postman测试了Python后端，效果很好。你知道吗

两台服务器都托管在Heroku上。节点服务器运行的是v8.1.4，Python服务器运行的是v3.5.6

下面是Python代码：

import os
from flask import Flask, request
from flask_cors import CORS, cross_origin

app = Flask(__name__)
CORS(app)

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

# prediction route
@app.route('/predict', methods=['POST', 'OPTIONS'])
@cross_origin()
def predict():
    req_image = request.files['image']
    # do stuff with req_image
    return prediction

#hosted locally for testing
if __name__ == '__main__':
    port = int(os.environ.get('PORT', 3001))
    app.run(host='0.0.0.0', port=port)

以及节点代码：

const config = require('../config/main');
const axios = require('axios');
const FormData = require('form-data');
const express = require('express');
const multer  = require('multer')
const upload = multer()
var predictionRouter = express.Router();

predictionRouter.use(upload.single('image'));
predictionRouter.post('/predict', function(req, res, next) {
  if (!req.file)
    throw new NoDataError('No image provided');

  var formData = new FormData();
  formData.append('image', req.file.buffer, {
    filename: 'image.png'
  });

  return axios.post(`${config.model.api_base_url}/predict`, formData, {
    headers: formData.getHeaders()
  })
  .then(results => res.status(200).send({ prediction: results.data }))
  .catch(err => {
    console.log(err)
    next(err)
  });
});

下面是Python错误：

2018-09-19T19:03:14.520797+00:00 heroku[router]: sock=backend at=error code=H18 desc="Server Request Interrupted" method=POST path="/predict" host=python-backend.herokuapp.com request_id=2dbaa4f2-3d58-4f84-ba60-83cf721fd803 fwd="130.15.59.3" dyno=web.1 connect=0ms service=103ms status=503 bytes=379 protocol=https
2018-09-19T19:03:14.434838+00:00 app[web.1]: 10.157.202.232 - - [19/Sep/2018:19:03:14 +0000] "POST /predict HTTP/1.1" 400 192 "-" "axios/0.18.0"

以及丑陋的节点错误：

{ Error: Request failed with status code 503
    at createError (/project/node_modules/axios/lib/core/createError.js:16:15)
    at settle (/project/node_modules/axios/lib/core/settle.js:18:12)
    at IncomingMessage.handleStreamEnd (/project/node_modules/axios/lib/adapters/http.js:201:11)
    at emitNone (events.js:110:20)
    at IncomingMessage.emit (events.js:207:7)
    at endReadableNT (_stream_readable.js:1047:12)
    at _combinedTickCallback (internal/process/next_tick.js:102:11)
    at process._tickCallback (internal/process/next_tick.js:161:9)
  config:
   { adapter: [Function: httpAdapter],
     transformRequest: { '0': [Function: transformRequest] },
     transformResponse: { '0': [Function: transformResponse] },
     timeout: 0,
     xsrfCookieName: 'XSRF-TOKEN',
     xsrfHeaderName: 'X-XSRF-TOKEN',
     maxContentLength: -1,
     validateStatus: [Function: validateStatus],
     headers:
      { Accept: 'application/json, text/plain, */*',
        'Content-Type': 'multipart/form-data; boundary=--------------------------087672685077373181485002',
        'User-Agent': 'axios/0.18.0' },
     method: 'post',
     url: 'https://python-backend.herokuapp.com/predict',
     data:
      FormData {
        _overheadLength: 151,
        _valueLength: 38528,
        _valuesToMeasure: [],
        writable: false,
        readable: true,
        dataSize: 0,
        maxDataSize: 2097152,
        pauseStreams: true,
        _released: true,
        _streams: [],
        _currentStream: null,
        _boundary: '--------------------------087672685077373181485002',
        _events: {},
        _eventsCount: 0 } },
  request:
   ClientRequest {
     domain: null,
     _events:
      { socket: [Function],
        abort: [Function],
        aborted: [Function],
        error: [Function],
        timeout: [Function],
        prefinish: [Function: requestOnPrefinish] },
     _eventsCount: 6,
     _maxListeners: undefined,
     output: [],
     outputEncodings: [],
     outputCallbacks: [],
     outputSize: 0,
     writable: true,
     _last: true,
     upgrading: false,
     chunkedEncoding: true,
     shouldKeepAlive: false,
     useChunkedEncodingByDefault: true,
     sendDate: false,
     _removedConnection: false,
     _removedContLen: false,
     _removedTE: false,
     _contentLength: null,
     _hasBody: true,
     _trailer: '',
     finished: true,
     _headerSent: true,
     socket:
      TLSSocket {
        _tlsOptions: [Object],
        _secureEstablished: true,
        _securePending: false,
        _newSessionPending: false,
        _controlReleased: true,
        _SNICallback: null,
        servername: null,
        npnProtocol: undefined,
        alpnProtocol: false,
        authorized: true,
        authorizationError: null,
        encrypted: true,
        _events: [Object],
        _eventsCount: 9,
        connecting: false,
        _hadError: false,
        _handle: null,
        _parent: null,
        _host: 'python-backend.herokuapp.com',
        _readableState: [Object],
        readable: false,
        domain: null,
        _maxListeners: undefined,
        _writableState: [Object],
        writable: false,
        allowHalfOpen: false,
        _bytesDispatched: 39047,
        _sockname: null,
        _pendingData: null,
        _pendingEncoding: '',
        server: undefined,
        _server: null,
        ssl: null,
        _requestCert: true,
        _rejectUnauthorized: true,
        parser: null,
        _httpMessage: [Circular],
        read: [Function],
        _consuming: true,
        _idleNext: null,
        _idlePrev: null,
        _idleTimeout: -1,
        [Symbol(asyncId)]: 45,
        [Symbol(bytesRead)]: 710 },
     connection:
      TLSSocket {
        _tlsOptions: [Object],
        _secureEstablished: true,
        _securePending: false,
        _newSessionPending: false,
        _controlReleased: true,
        _SNICallback: null,
        servername: null,
        npnProtocol: undefined,
        alpnProtocol: false,
        authorized: true,
        authorizationError: null,
        encrypted: true,
        _events: [Object],
        _eventsCount: 9,
        connecting: false,
        _hadError: false,
        _handle: null,
        _parent: null,
        _host: 'python-backend.herokuapp.com',
        _readableState: [Object],
        readable: false,
        domain: null,
        _maxListeners: undefined,
        _writableState: [Object],
        writable: false,
        allowHalfOpen: false,
        _bytesDispatched: 39047,
        _sockname: null,
        _pendingData: null,
        _pendingEncoding: '',
        server: undefined,
        _server: null,
        ssl: null,
        _requestCert: true,
        _rejectUnauthorized: true,
        parser: null,
        _httpMessage: [Circular],
        read: [Function],
        _consuming: true,
        _idleNext: null,
        _idlePrev: null,
        _idleTimeout: -1,
        [Symbol(asyncId)]: 45,
        [Symbol(bytesRead)]: 710 },
     _header: 'POST /predict HTTP/1.1\r\nAccept: application/json, text/plain, */*\r\nContent-Type: multipart/form-data; boundary=--------------------------087672685077373181485002\r\nUser-Agent: axios/0.18.0\r\nHost: python-backend.herokuapp.com\r\nConnection: close\r\nTransfer-Encoding: chunked\r\n\r\n',
     _onPendingData: [Function: noopPendingOutput],
     agent:
      Agent {
        domain: null,
        _events: [Object],
        _eventsCount: 1,
        _maxListeners: undefined,
        defaultPort: 443,
        protocol: 'https:',
        options: [Object],
        requests: {},
        sockets: [Object],
        freeSockets: {},
        keepAliveMsecs: 1000,
        keepAlive: false,
        maxSockets: Infinity,
        maxFreeSockets: 256,
        maxCachedSessions: 100,
        _sessionCache: [Object] },
     socketPath: undefined,
     timeout: undefined,
     method: 'POST',
     path: '/predict',
     _ended: true,
     res:
      IncomingMessage {
        _readableState: [Object],
        readable: false,
        domain: null,
        _events: [Object],
        _eventsCount: 3,
        _maxListeners: undefined,
        socket: [Object],
        connection: [Object],
        httpVersionMajor: 1,
        httpVersionMinor: 1,
        httpVersion: '1.1',
        complete: true,
        headers: [Object],
        rawHeaders: [Array],
        trailers: {},
        rawTrailers: [],
        upgrade: false,
        url: '',
        method: null,
        statusCode: 503,
        statusMessage: 'Service Unavailable',
        client: [Object],
        _consuming: true,
        _dumped: false,
        req: [Circular],
        responseUrl: 'https://python-backend.herokuapp.com/predict',
        redirects: [],
        read: [Function] },
     aborted: undefined,
     timeoutCb: null,
     upgradeOrConnect: false,
     parser: null,
     maxHeadersCount: null,
     _redirectable:
      Writable {
        _writableState: [Object],
        writable: true,
        domain: null,
        _events: [Object],
        _eventsCount: 2,
        _maxListeners: undefined,
        _options: [Object],
        _redirectCount: 0,
        _redirects: [],
        _requestBodyLength: 38735,
        _requestBodyBuffers: [],
        _onNativeResponse: [Function],
        _currentRequest: [Circular],
        _currentUrl: 'https://python-backend.herokuapp.com/predict' },
     [Symbol(outHeadersKey)]:
      { accept: [Array],
        'content-type': [Array],
        'user-agent': [Array],
        host: [Array] } },
  response:
   { status: 503,
     statusText: 'Service Unavailable',
     headers:
      { connection: 'close',
        server: 'Cowboy',
        date: 'Wed, 19 Sep 2018 19:03:14 GMT',
        'content-length': '506',
        'content-type': 'text/html; charset=utf-8',
        'cache-control': 'no-cache, no-store' },
     config:
      { adapter: [Function: httpAdapter],
        transformRequest: [Object],
        transformResponse: [Object],
        timeout: 0,
        xsrfCookieName: 'XSRF-TOKEN',
        xsrfHeaderName: 'X-XSRF-TOKEN',
        maxContentLength: -1,
        validateStatus: [Function: validateStatus],
        headers: [Object],
        method: 'post',
        url: 'https://python-backend.herokuapp.com/predict',
        data: [Object] },
     request:
      ClientRequest {
        domain: null,
        _events: [Object],
        _eventsCount: 6,
        _maxListeners: undefined,
        output: [],
        outputEncodings: [],
        outputCallbacks: [],
        outputSize: 0,
        writable: true,
        _last: true,
        upgrading: false,
        chunkedEncoding: true,
        shouldKeepAlive: false,
        useChunkedEncodingByDefault: true,
        sendDate: false,
        _removedConnection: false,
        _removedContLen: false,
        _removedTE: false,
        _contentLength: null,
        _hasBody: true,
        _trailer: '',
        finished: true,
        _headerSent: true,
        socket: [Object],
        connection: [Object],
        _header: 'POST /predict HTTP/1.1\r\nAccept: application/json, text/plain, */*\r\nContent-Type: multipart/form-data; boundary=--------------------------087672685077373181485002\r\nUser-Agent: axios/0.18.0\r\nHost: python-backend.herokuapp.com\r\nConnection: close\r\nTransfer-Encoding: chunked\r\n\r\n',
        _onPendingData: [Function: noopPendingOutput],
        agent: [Object],
        socketPath: undefined,
        timeout: undefined,
        method: 'POST',
        path: '/predict',
        _ended: true,
        res: [Object],
        aborted: undefined,
        timeoutCb: null,
        upgradeOrConnect: false,
        parser: null,
        maxHeadersCount: null,
        _redirectable: [Object],
        [Symbol(outHeadersKey)]: [Object] },
     data: '<!DOCTYPE html>\n\t<html>\n\t  <head>\n\t\t<meta name="viewport" content="width=device-width, initial-scale=1">\n\t\t<meta charset="utf-8">\n\t\t<title>Application Error</title>\n\t\t<style media="screen">\n\t\t  html,body,iframe {\n\t\t\tmargin: 0;\n\t\t\tpadding: 0;\n\t\t  }\n\t\t  html,body {\n\t\t\theight: 100%;\n\t\t\toverflow: hidden;\n\t\t  }\n\t\t  iframe {\n\t\t\twidth: 100%;\n\t\t\theight: 100%;\n\t\t\tborder: 0;\n\t\t  }\n\t\t</style>\n\t  </head>\n\t  <body>\n\t\t<iframe src="//www.herokucdn.com/error-pages/application-error.html"></iframe>\n\t  </body>\n\t</html>' } }
Error: Request failed with status code 503
    at createError (/project/node_modules/axios/lib/core/createError.js:16:15)
    at settle (/project/node_modules/axios/lib/core/settle.js:18:12)
    at IncomingMessage.handleStreamEnd (/project/node_modules/axios/lib/adapters/http.js:201:11)
    at emitNone (events.js:110:20)
    at IncomingMessage.emit (events.js:207:7)
    at endReadableNT (_stream_readable.js:1047:12)
    at _combinedTickCallback (internal/process/next_tick.js:102:11)
    at process._tickCallback (internal/process/next_tick.js:161:9)
POST /api/predictions/predict 500 443.837 ms - 74