==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.3.1 MARIADB edition.
- Deployed with iRedMail Easy or the downloadable installer? downloadable installer
- Linux/BSD distribution name and version: Centos 8.2
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MARIADB
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? no
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

While installing the iRedmail steps are missing in installation document.
> Web server only shows nginx or no web server option (step missing on document)
>MySQL is replaced by mariyadb (document shows MySQL)
> below are extra step where I have choose yes (step missing on document)
[ INFO ] Disable SELinux in /etc/selinux/config.
< Question > Would you like to use firewall rules provided by iRedMail?
< Question > File: /etc/firewalld/zones/iredmail.xml, with SSHD ports: 22. [Y|nY
[ INFO ] Copy firewall sample rules.
< Question > Restart firewall now (with ssh ports: 22)? [y|N]Y
[ INFO ] Restarting firewall ...
< Question > Would you like to use MySQL configuration file shipped within iRedMail now?
< Question > File: /etc/my.cnf. [Y|n]Y

while installation got below error
[ INFO ] Installing required Python-2 modules with pip2: web.py>=0.51 more-itert                                                                             ools==5.0.0 web.py>=0.51 more-itertools==5.0.0 uwsgi>=2.0.18 pycurl>=7.43.0.5 Py                                                                             MySQL>=0.9.3
WARNING: Running pip install with root privileges is generally not a good idea.                                                                              Try `pip2 install --user` instead.
Collecting web.py>=0.51
  Using cached https://files.pythonhosted.org/packages … 80157e5463                                                                             07f8884009db614f50d9fe01eab70d080944bbe2b/web.py-0.60.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-rblEki/web.py/setup.py", line 7, in <module>
        from web import __version__
      File "web/__init__.py", line 4, in <module>
        from . import (  # noqa: F401
      File "web/db.py", line 771
        print("ERR:", str(sql_query), file=debug)
                                          ^
    SyntaxError: invalid syntax

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-rb                                                                             lEki/web.py/

my old iredmail is on MySQL. How we can migrate the data to mariadb or there is an option to install MySQL.

Does Centos 8 is compatible with iredmail and no issue later when in production as I was reading in this form that Centos 8 has issues with iredmail. 

accessing iredadmin shows 502 Bad Gateway error and log shows below error

[error] 953#0: *909 connect() failed (111: Connection refused) while connecting to upstream, client: IP, server: _, request: "GET /iredadmin/ HTTP/1.1", upstream: "uwsgi://127.0.0.1:7791", host: "IP"