Setup nginx + flask load balancer

nginx config

…
upstream backend{
server 127.0.0.1:90;
server 127.0.0.1:91;
}
…
server {
listen 81 default_server;
listen [::]:81 default_server;
location / {
proxy_pass http://backend;
}
}
…

flask sample server to test

s1.py (simulate server 1)

from flask import Flask
app = Flask(__name__)
@app.route('/')
def helloIndex():
    return 'Hello World from server1'
app.run(host='0.0.0.0', port=90)

s2.py (simulate server 2)

from flask import Flask
app = Flask(__name__)
@app.route('/')
def helloIndex():
    return 'Hello World from server2'
app.run(host='0.0.0.0', port=91)

The fix of issue : connect() to 127.0.0.1:90 failed (13: Permission denied) while connecting to upstream :

> setsebool httpd_can_network_connect on

result :

default balance strategy is using weight, and each server weight=1 . so half request will be routed to server1 and another half to server2 .

so if change nginx config as below .

upstream backend{
server 127.0.0.1:90 weight=2;
server 127.0.0.1:91 weight=1;
}

2/3 request will be routed to port 90 and 1/3 to port 91. results like blow

other balancing stategies

least_conn: As the name tells, directs the requests to the server with the least active connections at that time.

ip_hash: IP hashing uses the visitors IP address as a key to determine which host should be selected to service the request. This allows the visitors to be each time directed to the same server(unless it is down)

That’s all .

Thanks for reading !