Symptoms
When an URL powered by Magento is accessed, following error is thrown:
SQLSTATE[HY000] [2002] Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
Cause
Magento configuration files, located at
/usr/local/pem/vhosts/<WEBSPACE_ID>/webspace/siteapps/magento-12345/htdocs/app/etc/local.xml
/usr/local/pem/vhosts/<WEBSPACE_ID>/webspace/siteapps/magento-12345/htdocs/app/etc/local_myserver.xml
Contain incorrect database access credentials (here 12345 is the application instance ID, can be different in each case).
Resolution
Set the access credentials correctly. Passwords for databases managed by POA can be updated in Customer's Control Panel, More Services > Databases.