Could no connect to the database: SQLSTATE[HY000] [2002] No route to host

#0  Helpers::debugStringBacktrace() called at [/html/system/core/library/Helpers.php:44]
#1  Helpers::fatalError(Could no connect to the database: SQLSTATE[HY000] [2002] No route to host) called at [/html/system/core/library/Db.php:63]
#2  Db::getPDO() called at [/html/system/core/library/Pages.php:28]
#3  Pages->__construct() called at [/html/system/custom/frontend/modules/navigation.php:17]
#4  VenusNavigationFrontendModule->__construct() called at [/html/system/core/library/FrontendModules.php:41]
#5  FrontendModules::loadClass(navigation, /html/system/custom/frontend/modules/navigation.php, VenusNavigationFrontendModule) called at [/html/system/core/library/FrontendModules.php:51]
#6  FrontendModules::load() called at [/html/system/core/frontend/index.php:33]
#7  require_once(/html/system/core/frontend/index.php) called at [/html/index.php:97]