Admin Area shows 502 Bad Gateway

[dEbo1]

After yesterday autoupdate (to Plesk 12.0.18 Update 48) admin area shows:
502 Bad Gateway
nginx

While navigating to Tools & Settings:
ERROR: Zend_Controller_Exception: SQLSTATE[HY000] [2002] Connection refused#0 /usr/local/psa/admin/externals/Zend/Db/Adapter/Pdo/Mysql.php(109): Zend_Db_Adapter_Pdo_Abstract->_connect()
#1 /usr/local/psa/admin/externals/Zend/Db/Adapter/Abstract.php(459): Zend_Db_Adapter_Pdo_Mysql->_connect()
#2 /usr/local/psa/admin/externals/Zend/Db/Adapter/Pdo/Abstract.php(238): Zend_Db_Adapter_Abstract->query(Object(Zend_Db_Table_Select), Array)
#3 /usr/local/psa/admin/plib/Db/Adapter/Pdo/Mysql.php(19): Zend_Db_Adapter_Pdo_Abstract->query(Object(Zend_Db_Table_Select), Array)
#4 /usr/local/psa/admin/externals/Zend/Db/Table/Abstract.php(1534): Db_Adapter_Pdo_Mysql->query(Object(Zend_Db_Table_Select))
#5 /usr/local/psa/admin/externals/Zend/Db/Table/Abstract.php(1349): Zend_Db_Table_Abstract->_fetch(Object(Zend_Db_Table_Select))
#6 /usr/local/psa/admin/plib/CommonPanel/Controller/Helper/Module.php(161): Zend_Db_Table_Abstract->fetchAll()
#7 /usr/local/psa/admin/plib/CommonPanel/Controller/Helper/Module.php(186): CommonPanel_Controller_Helper_Module::_eachModule(Object(Closure))
#8 /usr/local/psa/admin/plib/CommonPanel/Controller/Helper/Module.php(51): CommonPanel_Controller_Helper_Module::_eachModuleContent(Object(Closure), 'ContentInclude')
#9 /usr/local/psa/admin/plib/CommonPanel/Controller/Action/Abstract.php(59): CommonPanel_Controller_Helper_Module::initRendering()
#10 /usr/local/psa/admin/plib/AdminPanel/Controller/Action/Abstract.php(32): CommonPanel_Controller_Action_Abstract->init()
#11 /usr/local/psa/admin/plib/AdminPanel/Controller/Action/Admin.php(55): AdminPanel_Controller_Action_Abstract->init()
#12 /usr/local/psa/admin/application/admin/controllers/ErrorController.php(18): AdminPanel_Controller_Action_Admin->init()
#13 /usr/local/psa/admin/externals/Zend/Controller/Action.php(133): Admin_ErrorController->init()
#14 /usr/local/psa/admin/externals/Zend/Controller/Dispatcher/Standard.php(268): Zend_Controller_Action->__construct(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http), Array)
#15 /usr/local/psa/admin/externals/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#16 /usr/local/psa/admin/plib/Application/Web.php(38): Zend_Controller_Front->dispatch(NULL)
#17 /usr/local/psa/admin/htdocs/application.php(15): Plesk\Application_Web->run()
#18 {main


Only error log i was able to find:
# tail -f /var/log/sw-cp-server/error_log log
==> /var/log/sw-cp-server/error_log <==
2015/05/28 12:17:36 [error] 2433#0: *98 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: xx.xx.xx.xx, server: , request: "GET /admin/home/admin HTTP/1.1", upstream: "fastcgi://unix:/var/run/sw-engine.sock:", host: "our.host.com:8443", referrer: "https://our.host.com:8443/left.php3"

Restarted all services, nothing helped
Any suggestions?

Plesk for Linux version 12.0.18
CentOS 6.6 2.6.32-504.16.2.el6.x86_64

 

[IgorG]

[2002] Connection refused#0

Most probably that this problem related to firewall. Do you have enabled any specific rules? Try to disable firewall completely and check how it goes on.