Partial hostname change prevents httpd.conf rebuild

Symptoms

You receive an error similar to the following when rebuilding the Apache configuration, and the hostname in the error doesn't match the server's hostname.

Bad configuration file located at /etc/apache2/conf/httpd.conf.work.4cd5684f
Error:
The “/usr/sbin/httpd -DSSL -t -f /etc/apache2/conf/httpd.conf.work.4cd5684f.cfgcheck -C Include "/etc/apache2/conf.modules.d/*.conf"” command (process 1383) reported error number 1 when it ended.
Configuration problem detected on line 219 of file /etc/apache2/conf/httpd.conf.work.4cd5684f:	RemoteIP: Error parsing IP server.domain.tld (Name or service not known error) for RemoteIPInternalProxy

	--- /etc/apache2/conf/httpd.conf.work.4cd5684f ---
	213# This allows us to not log requests proxied to Apache from nginx;
	214#    That way hits are not double recorded.
	215SetEnvIf cPanel-localhost DBTbOahLsCHIWgxm7vhO8w3rNNgUmWafg22hUHD83xkbL3-wiIwu7Cu9Kvxm5FTT isproxyrequest
	216RequestHeader unset cPanel-localhost
	217<IfModule remoteip_module>
	218    RemoteIPHeader X-Forwarded-For-DBTbOahLsCHIWgxm7vhO8w3rNNgUmWafg22hUHD83xkbL3-wiIwu7Cu9Kvxm5FTT
	219 ===>     RemoteIPInternalProxy server.localhost.com <===
	220    RequestHeader unset X-Forwarded-For-DBTbOahLsCHIWgxm7vhO8w3rNNgUmWafg22hUHD83xkbL3-wiIwu7Cu9Kvxm5FTT
	221</IfModule>
	222
	223<IfModule mod_log_config.c>
	224    LogFormat "%v:%p %h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combinedvhost
	225    <IfModule logio_module>
	--- /etc/apache2/conf/httpd.conf.work.4cd5684f ---

[root@server ~]cPs# hostname
new.domain.tld
[root@server ~]cPs#

Description

This issue occurs when the server's hostname is partially changed. Resetting the hostname will correct the issue.

Workaround

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.
2. Run the following command to sync the new hostname across the server's configurations.

   /usr/local/cpanel/bin/set_hostname $new.domain.tld

3. Rebuild the Apache configuration.

   /usr/local/cpanel/scripts/rebuildhttpdconf

4. Restart the web server.

   /usr/local/cpanel/scripts/restartsrv_httpd

Additional resources

What is an effective hostname?