Website is not accessible when firewall is enabled on Plesk server: Site can’t be reached

Symptoms

1. RHEL7/CentOS 7 is used.
2. Website points to correct IP address, but not accessible:

   Site can't be reached

3. Curl utility shows the following:

   # curl -I http://example.com -v
   * About to connect() to example.com port 80 ( #0 )
   *  Trying 203.0.113.2… No route to host
   * couldn’t connect to host
   * Closing connection #0
   curl: (7) couldn’t connect to host

4. Traceroute utility shows the following:

   # traceroute -T -p 80 example.com
   traceroute to example.com (203.0.113.2), 30 hops max, 60 byte packets
   1  gw4.example2.com (1.1.1.1)  0.211 ms  0.204 ms  0.250 ms
   2  nsl-example3.com (2.2.2.2)  0.524 ms  0.369 ms  0.509 ms
   16  * * *
   17  * * *
   18  * * *
   19  * * web18.example4.com (3.3.3.3)  302.789 ms !X <——– “communication administratively prohibited”

5. HTTP service is not allowed on local firewall:

   # firewall-cmd –list-services | grep http
   #

Cause

Local firewall blocks connections to HTTP service.

Resolution

1. Login to the server over SSH
2. Allow HTTP service:

   # firewall-cmd –permanent –add-service=http
   success
   # firewall-cmd –reload
   success
   # firewall-cmd –list-services
   ssh dhcpv6-client http