Intermittent 503 error when accessing WHM/cPanel

Symptoms

Attempting to access WHM/cPanel will intermittently give 503 errors, and an entry similar to the following can be found in the cPanel error log.

info [cpsrvd] Internal Server Error: "-" 503 The server is too busy to handle your 
request. Please wait a few minutes and try again.

Description 

The 503 errors occur when the server receives too many simultaneous connections on ports 2082, 2083, 2086, 2087, 2095, and 2096.

Workaround

If the connections are caused by legitimate traffic, increasing the "Max cPanel/WHM/Webmail service handlers" value in "Tweak Settings" can correct this behavior. If you cannot log into WHM to change this value because of the 503 errors, you can change the settings from the command line.

1. Access the server's command line as the 'root' user via SSH.
2. Run the following command.

   whmapi1 set_tweaksetting key=maxcpsrvdconnections value=newvalue

   Please note that "newvalue" must be replaced with the desired value. The default value is 200, with a maximum value of 16,384. If the value is less than 200, the server will revert the value to the default value.

Additional resources

The cpanel.config File: Keys and default settings