Cannot access Updates & Upgrades page: ERR_CONNECTION_TIMED_OUT

Symptoms

• Cannot open the Updates & Upgrades page:

  CONFIG_TEXT: This site can’t be reached
  ERR_CONNECTION_TIMED_OUT

• Updates & Upgrades redirects to https://example.com:8447;
• The https://203.0.113.2:8447 is opening successfully;
• DNS are managed by CloudFlare:

  # dig +trace servername.com
  
  ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.62.rc1.el6_9.2 <<>> +trace servername.com
  ;; global options: +cmd
  ...
  servername.com. 172800 IN NS john.ns.cloudflare.com.
  servername.com. 172800 IN NS dell.ns.cloudflare.com.
  ;; Received 173 bytes from 2001:500:d937::30#53(2001:500:d937::30) in 100 ms
  servername.com. 300 IN A 104.18.50.15 <<<< CloudFlare IP address
  servername.com. 300 IN A 104.18.51.15 <<<< CloudFlare IP address
  ;; Received 65 bytes from 2400:cb00:2049:1::adf5:3bb9#53(2400:cb00:2049:1::adf5:3bb9) in 98 ms

  Note: it is possible to check DNS records of the servername.com using online tools.

Cause

Incorrect settings on the CloudFlare side.

Resolution

Open the port 8447 on CloudFlare side or connect to the installer directly using the server IP address. 

Contact CloudFlare support for more information - https://support.cloudflare.com/