scale up Flask apps with gevent asynchronous I/O

Gevent is the use of simple, sequential programming in python to achieve scalability provided by asynchronous IO and lightweight multi-threading (as opposed to the callback-style of programming using Twisted’s Deferred).
It is built on top of libevent/libev (for asynchronous I/O) and greenlets (lightweight cooperative multi-threading).
we can use pip install gevent to install it.
Here is the sample.py:

from gevent import monkey
monkey.patch_all()
from flask import Flask
from gevent import pywsgi
app = Flask(__name__)
@app.route('/')
def hello():
    return "Hello World!"
if __name__ == '__main__':
    #app.run()
    server = pywsgi.WSGIServer(("0.0.0.0", 8080), app)
    server.serve_forever()                            

you can run it in background:
nohup python3 sample.py &
then you can open the sample app on http://your_server_ip:8080

Use ApacheBench To Do Load Testing:
1. apt-get install apache2-utils
2. ab -r -n 2000 -c 200 http://127.0.0.1:8080/?delay=1

Concurrency Level:      200
Time taken for tests:   2.470 seconds
Complete requests:      2000
Failed requests:        0
Total transferred:      294000 bytes
HTML transferred:       24000 bytes
Requests per second:    809.60 [#/sec] (mean)
Time per request:       247.035 [ms] (mean)
Time per request:       1.235 [ms] (mean, across all concurrent requests)
Transfer rate:          116.22 [Kbytes/sec] received

compare it with sample_old.py without gevent:

from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello():
    return "Hello World!"
if __name__ == '__main__':
    app.run(port=8080)

run same ab command, you will get:

Concurrency Level:      200
Time taken for tests:   4.493 seconds
Complete requests:      2000
Failed requests:        0
Total transferred:      330000 bytes
HTML transferred:       24000 bytes
Requests per second:    445.10 [#/sec] (mean)
Time per request:       449.340 [ms] (mean)
Time per request:       2.247 [ms] (mean, across all concurrent requests)
Transfer rate:          71.72 [Kbytes/sec] received

Time per request reduced from 449ms to 247ms!
ref: https://iximiuz.com/en/posts/flask-gevent-tutorial/