I am trying to mount a server ready for production using Nginx, Docker and Supervisor.

The problem I'm facing is, even if it works and I can see index.html in my browser, this error is showing all time:
2016/08/28 12:05:12 [emerg] 12#12: bind() to [::]:80 failed (98: Address in use) nginx: [emerg] bind() to [::]:80 failed (98: Address in use)

The dockerfile:

FROM nginx:stable-alpine

RUN rm -f /etc/nginx/conf.d/* && mkdir -p /var/www/app
COPY config/nginx.conf /etc/nginx/conf.d/
COPY config/supervisord.conf /supervisord.conf
COPY scripts /scripts
RUN chmod -R 700 /scripts

CMD [ "/scripts/start" ]

In /scripts/start I have this:

#!/bin/bash
supervisord -n -c /supervisord.conf

Then in supervisord.conf:

[unix_http_server]
file=/dev/shm/supervisor.sock   ; (the path to the socket file)

[supervisord]
logfile=/tmp/supervisord.log ; (main log file;default $CWD/supervisord.log)
logfile_maxbytes=50MB        ; (max main logfile bytes b4 rotation;default 50MB)
logfile_backups=10           ; (num of main logfile rotation backups;default 10)
loglevel=info                ; (log level;default info; others: debug,warn,trace)
pidfile=/tmp/supervisord.pid ; (supervisord pidfile;default supervisord.pid)
nodaemon=false               ; (start in foreground if true;default false)
minfds=1024                  ; (min. avail startup file descriptors;default 1024)
minprocs=200                 ; (min. avail process descriptors;default 200)
user=root                    ;

[rpcinterface:supervisor]
supervisor.rpcinterface_factory = supervisor.rpcinterface:make_main_rpcinterface

[program:nginx]
command=/usr/sbin/nginx
autostart=true
autorestart=true
priority=10
stdout_events_enabled=true
stderr_events_enabled=true
stdout_logfile=/dev/stdout
stdout_logfile_maxbytes=0
stderr_logfile=/dev/stderr
stderr_logfile_maxbytes=0

And when I run docker (without daemon -d option), I got this terminal output:

2016-08-28 12:05:10,474 CRIT Set uid to user 0
2016-08-28 12:05:10,481 INFO RPC interface 'supervisor' initialized
2016-08-28 12:05:10,481 CRIT Server 'unix_http_server' running without any HTTP authentication checking
2016-08-28 12:05:10,481 INFO supervisord started with pid 6
2016-08-28 12:05:11,484 INFO spawned: 'nginx' with pid 9
2016-08-28 12:05:11,497 INFO exited: nginx (exit status 0; not expected)
2016-08-28 12:05:12,499 INFO spawned: 'nginx' with pid 12
2016/08/28 12:05:12 [emerg] 12#12: bind() to 0.0.0.0:80 failed (98: Address in use)
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address in use)
2016/08/28 12:05:12 [emerg] 12#12: bind() to [::]:80 failed (98: Address in use)
nginx: [emerg] bind() to [::]:80 failed (98: Address in use)
........

It seems like it spawned 2 nginx processes instead of one because first said it died by no reason, but in fact it wasn't dead.