Steps to reproduce:

1. Install a brand new server or VM using CentOS 7 18.10, "Minimal install" option
2. Install Zabbix 4.0.3 for CentOS 7 + PostgreSQL, using the official docs:
   https://www.zabbix.com/download?zabbix=4.0&os_distribution=centos&os_version=7&db=PostgreSQL
3. The problem occurs here, as the user won't really be able to access the front end, nor will the server be working on the backend, as the docs don't include critical information needed for Zabbix to function.

Result:
1. Zabbix isn't accessible to the end user as no port(s) have been opened on the firewall by the instructions.
`# firewall-cmd --zone=public --add-port=80/tcp` will fix that

2. The Zabbix server isn't able to communicate with the various daemons and services it needs, due to missing SELinux settings

• So far (still working through the process now), these are helping:
  `# setsebool -P httpd_can_network_connect 1`
  `# setsebool -P daemons_enable_cluster_mode 1`

As a first thought, these should probably either be added to some rpm scripting that runs automatically during install, or at least mentioned in the install instructions before the final step where things are started "f. Start Zabbix server and agent processes".

Mostly surprised this isn't already in place, as the above is kind of mandatory to have for the server to even run.  Unless people commonly disable SELinux, which isn't generally a good idea.