CODEWITHSUNDEEP
pythonflaskwsgiserver-sent-eventsevent-stream
Vincent K. Deli
Vincent K. Deli

Reputation: 1

How do I implement proper Flask server that contains Server-Sent-Event API?

[Flask SSE API doesn't work on production]

Hi, i'm facing an issue in my flask application where I have multiple regular APIs and 1 HTTP API that sends SSE to my React app. In my local development env, the app works just fine as expected. However, when I deployed it to CPanel shared hosting, I noticed that the the React app makes proper request of Content-Type text/event-stream, but received text/html response header from the API after 2 minute timeout. Is there anything wrong with how I implemented the server?

main.py

from myapplication import create_app
from flask import stream_with_context
from gevent import monkey; monkey.patch_all()
from gevent.pywsgi import WSGIServer

app = create_app()

if __name__ == '__main__':
  http_server = WSGIServer(("localhost", 5000), app)
  http_server.serve_forever()

myapplication/init.py

from flask import Flask
from flask_cors import CORS
from flask_sqlalchemy import SQLAlchemy
from os import path, environ
from dotenv import load_dotenv

db = SQLAlchemy()
DATABASE_NAME = 'database.db'
load_dotenv()

def get_database_uri():
  host = environ['DB_HOST']
  port = environ['DB_PORT']
  name = environ['DB_NAME']
  username = environ['DB_USER']
  password = environ['DB_PASS']
  return f'postgresql+psycopg2://{username}:{password}@{host}:{port}/{name}'

def create_database(app):
  if not path.exists('myapplication/' + DATABASE_NAME):
    db.create_all(app=app)
    print('Database created.')

def create_app():
  app = Flask(__name__)
  CORS(app)
  cors = CORS(app, resource = {
    r"/*": {
      "origins": "*"
    }
  })
  app.config['SECRET_KEY'] = environ['SECRET_KEY']
  app.config['SQLALCHEMY_DATABASE_URI'] = get_database_uri()

  db.init_app(app)

  from .gallery import gallery
  from .document import document
  from .timer import timer
  from .member import member

  app.register_blueprint(gallery, url_prefix='/gallery')
  app.register_blueprint(document, url_prefix='/document')
  app.register_blueprint(timer, url_prefix='/timer')
  app.register_blueprint(member, url_prefix='/member')

  from .models import Member, Gallery, Document, Timer
  create_database(app)

  return app

timer.py (SSE api)

global_count = '60'
global_refresh_count = '0'

@timer.route('/stream')
def get_current_stream():
  def send_event():
    while True:
      event_payload = '{"count": "%s", "refreshCount": "%s"}'%(global_count, global_refresh_count)
      data_message = f'data: {str(event_payload)}\n\n'
      yield data_message
      time.sleep(1)
  return Response(send_event(), mimetype='text/event-stream')

Local development response: dev response Local development eventstream response: dev event stream response

Production response: prod response

CPanel python app setup: Application startup file: passenger_wsgi.py Application Entry point: application

passenger_wsgi.py

import imp
import os
import sys


sys.path.insert(0, os.path.dirname(__file__))

wsgi = imp.load_source('wsgi', 'main.py')
application = wsgi.app

Please kindly help guide me folks, much appreciated!

Upvotes: 0

Views: 1450

Answers (1)

Collin Ahn
Collin Ahn

Reputation: 11

you have to set certain headers like below

resp = Response(
        send_event(),
        mimetype='text/event-stream'
    )
resp.headers['X-Accel-Buffering'] = 'no'
resp.headers['Cache-Control'] = 'no-cache'
return resp

and configure setting throughout your service

for example in case of nginx:

 location '/' {
        proxy_buffering off;
        proxy_cache off;
        proxy_read_timeout 12h;
        ...
        proxy_pass {your_route};
    }

in case of gunicorn: set timeout param to 0 when you execute it.

/{path_to}/gunicorn --workers {num_workers} --timeout 0 --bind {path} -m 007 {module}:{app_name}

Upvotes: 1

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