id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
2014	nginx dynamic configuration reload is jittery	udaysha01@…		"I am trying to use nginx as a reverse proxy, listening on a port and forwarding all incoming requests to a service running on another port. I want to change the configuration and update which service nginx is passing the incoming traffic to, but when I update the configuration, nginx doesn't switch cleanly from the old service to the new service. It switches back and forth a number of times before eventually settling on the new service.

Steps to reproduce: First create the following files.

Just a simple nginx config file.
nginx.conf:
{{{
events {}

http {
  server {
    listen 1970;
    location / {
      proxy_pass http://127.0.0.1:3000;
    }
  }
}
}}}

A dummy service which listens and logs the path of each http request. Also generates a UUID which it sends back along with every response.
listen.py:
{{{
#!/usr/bin/env python3

import http.server as SimpleHTTPServer
import socketserver as SocketServer
import logging
import sys
import os
import uuid

#PORT = int(sys.argv[1])
PORT = int(sys.argv[1])
me = str(uuid.uuid4())

class GetHandler(
        SimpleHTTPServer.SimpleHTTPRequestHandler
        ):

    def log_message(self, format, *args):
        pass

    def do_GET(self):
        print(me + "": "" + self.path)
        self.send_response(200)
        self.end_headers()
        self.wfile.write(bytes(""ok "" + me + ""\n"", ""utf-8""))

Handler = GetHandler
httpd = SocketServer.TCPServer(("""", PORT), Handler)
try:
    httpd.serve_forever()
except KeyboardInterrupt:
    pass

httpd.server_close()
}}}

A script which sends requests one after the other to nginx. It looks at the UUID reported in the response to figure out which service responded to the request, and logs whenever the responding service changes.
spammer.py:
{{{
#!/usr/bin/python3

import requests
from time import sleep
PORT= ""1970""
i = 0
pid = 0
while True:
    URL = ""http://localhost:"" + PORT + ""/"" + str(i)
    r = requests.get(url = URL)
    if r.content[:2] != b""ok"":
        print(""Failed at %d"" % i)
        break
    if r.content[2:-1] != pid:
        pid = r.content[2:-1]
        print(""New responder: %s at %d"" % (pid, i))
    i += 1
}}}

1. Run nginx via: nginx -c $(pwd)/nginx.conf -g ""pid $(pwd)/nginx.pid; daemon off;""
2. Start two copies of listen.py with: python listen.py 3000 && python listen.py 3001
3. Start a copy of spammer.py with: python spammer.py
4. Edit the port number in nginx.conf - change it from 3000 to 3001
5. Tell nginx to reload configuration via: kill -HUP $(cat nginx.pid)
6. Observe the ""jitter"" by looking at the output of spammer.py. Actual output is something like
{{{
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 0
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21948
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 21951
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21952
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 21953
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21955
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 21956
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21965
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 21966
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21967
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 21974
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21977
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 21993
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21997
}}}
while the expected output would be more like
{{{
New responder: b' affe8cf0-0ae5-4565-8e20-a237367f5e83' at 0
New responder: b' 7553a5ad-6875-4903-9b15-533bd4faf53f' at 21948
}}}"	defect	closed	minor		nginx-core	1.18.x	invalid			Linux uday-arch 5.6.8-arch1-1 #1 SMP PREEMPT Wed, 29 Apr 2020 16:22:56 +0000 x86_64 GNU/Linux	"nginx version: nginx/1.18.0
built with OpenSSL 1.1.1g  21 Apr 2020
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --conf-path=/etc/nginx/nginx.conf --sbin-path=/usr/bin/nginx --pid-path=/run/nginx.pid --lock-path=/run/lock/nginx.lock --user=http --group=http --http-log-path=/var/log/nginx/access.log --error-log-path=stderr --http-client-body-temp-path=/var/lib/nginx/client-body --http-proxy-temp-path=/var/lib/nginx/proxy --http-fastcgi-temp-path=/var/lib/nginx/fastcgi --http-scgi-temp-path=/var/lib/nginx/scgi --http-uwsgi-temp-path=/var/lib/nginx/uwsgi --with-cc-opt='-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -D_FORTIFY_SOURCE=2' --with-ld-opt=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now --with-compat --with-debug --with-file-aio --with-http_addition_module --with-http_auth_request_module --with-http_dav_module --with-http_degradation_module --with-http_flv_module --with-http_geoip_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_mp4_module --with-http_realip_module --with-http_secure_link_module --with-http_slice_module --with-http_ssl_module --with-http_stub_status_module --with-http_sub_module --with-http_v2_module --with-mail --with-mail_ssl_module --with-pcre-jit --with-stream --with-stream_geoip_module --with-stream_realip_module --with-stream_ssl_module --with-stream_ssl_preread_module --with-threads"