Error in cronjob for archiving job (no replies)

I posted it already under "general questions" but here is the better group:

Hi,

my crontab on our piwik installation server (Linux SLES11) is the following:
5 * * * * /usr/bin/php /srv/www/vhosts/lxapp57.esag.net/project/piwik/console core:archive --url=http://lxapp57.esag.net/project/piwik/ > /srv/www/vhosts/lxapp57.esag.net/project/piwik/piwik-archive.log
--> So the job runs 5 mins past every hour.

As admin I got about 3 times a day the following mail with the following error text:

ERROR CoreConsole[2015-01-02 04:05:11] [3e6ee] Got invalid response from API request: http://lxapp57.esag.net/project/piwik/index.php?module=API&method=API.get&idSite=1&period=month&date=last2&format=php&token_auth=c0e024d9200b5705bc4804722636378a&trigger=archivephp. Response was '<div style='word-wrap: break-word; border: 3px solid red; padding:4px; width:70%; background-color:#FFFF96;'> <strong>There is an error. Please report the message (Piwik 2.9.1) and full backtrace in the <a href='?module=Proxy&action=redirect&url=http://forum.piwik.org' target='_blank'>Piwik forums</a> (please do a Search first as it might have been reported already!).<br /><br/> Warning:</strong> <em>file_get_contents(): php_network_getaddresses: getaddrinfo failed: Name or service not known</em> in <strong>/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Http.php</strong> on line <strong>408</strong> <br /><br />Backtrace --&gt;<div style="font-family:Courier;font-size:10
pt"><br /> #0 Piwik\Error::errorHandler(...) called at [:]<br /> #1 file_get_contents(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Http.php:408]<br /> #2 Piwik\Http::sendHttpRequestBy(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Http.php:94]<br /> #3 Piwik\Http::sendHttpRequest(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/UpdateCheck.php:72]<br /> #4 Piwik\UpdateCheck::check(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/plugins/CoreUpdater/CoreUpdater.php:156]<br /> #5 Piwik\Plugins\CoreUpdater\CoreUpdater->updateCheck(...) called at [:]<br /> #6 call_user_func_array(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/EventDispatcher.php:121]<br /> #7 Piwik\EventDispatcher->postEvent(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Piwik.php:684]<br /> #8 Piwik\Piwik::postEvent(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Fr
ontController.php:451]<br /> #9 Piwik\FrontController->init(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/dispatch.php:35]<br /> #10 require_once(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/index.php:46]<br /> #11 require_once(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/CliMulti/RequestCommand.php:53]<br /> #12 Piwik\CliMulti\RequestCommand->execute(...) called at
[/srv/www/vhosts/lxapp57.esag.net/project/piwik/vendor/symfony/console/Symfony/Component/Console/Command/Command.php:252]<br /> #13 Symfony\Component\Console\Command\Command->run(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/vendor/symfony/console/Symfony/Component/Console/Application.php:889]<br /> #14 Symfony\Component\Console\Application->doRunCommand(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/vendor/symfony/console/Symfony/Component/Console/Application.php:193]<br /> #15 Symfony\Component\Console\Applica
tion->doRun(...) called at [:]<br /> #16 call_user_func(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Console.php:60]<br /> #17 Piwik\{closure}(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Access.php:454]<br /> #18 Piwik\Access::doAsSuperUser(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Console.php:61]<br /> #19 Piwik\Console->doRun(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/vendor/symfony/console/Symfony/Component/Console/Application.php:124]<br /> #20 Symfony\Component\Console\Application->run(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/console:30]<br /> </div><br /> </pre></div><br /> <div style='word-wrap: break-word; border: 3px solid red; padding:4px; width:70%; background-color:#FFFF96;'> <strong>There is an error. Please report the message (Piwik 2.9.1) and full backtrace in the <a href='?module=Proxy&action=redirect&url=http://forum.piwik.
org' target='_blank'>Piwik forums</a> (please do a Search first as it might have been reported already!).<br /><br/> Warning:</strong> <em>file_get_contents(): php_network_getaddresses: getaddrinfo failed: Name or service not known</em> in <strong>/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Http.php</strong> on line <strong>408</strong> <br /><br />Backtrace --&gt;<div style="font-family:Courier;font-size:10pt"><br /> #0 Piwik\Error::errorHandler(...) called at [:]<br /> #1 file_get_contents(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Http.php:408]<br /> #2 Piwik\Http::sendHttpRequestBy(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Http.php:94]<br /> #3 Piwik\Http::sendHttpRequest(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/UpdateCheck.php:72]<br /> #4 Piwik\UpdateCheck::check(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/plugins/CoreUpdater/CoreUpdater.php:156]<br />
#5 Piwik\Plugins\CoreUpdater\CoreUpdater->updateCheck(...) called at [:]<br /> #6 call_user_func_array(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/EventDispatcher.php:121]<br /> #7 Piwik\EventDispatcher->postEvent(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/Piwik.php:684]<br /> #8 Piwik\Piwik::postEvent(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/FrontController.php:451]<br /> #9 Piwik\FrontController->init(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/dispatch.php:35]<br /> #10 require_once(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/index.php:46]<br /> #11 require_once(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/core/CliMulti/RequestCommand.php:53]<br /> #12 Piwik\CliMulti\RequestCommand->execute(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/piwik/vendor/symfony/console/Symfony/Component/Console/Command/Command.php:252]<br /
> #13 Symfony\Component\Console\Command\Command->run(...) called at [/srv/www/vhosts/lxapp57.esag.net/project/p
ERROR CoreConsole[2015-01-02 04:05:15] [3e6ee] 1 total errors during this script execution, please investigate and try and fix these errors.

At the other times it is running without errors. Could you please give me a hint, what is wrong configured in our installation?

Thx in advance and kind regards,
Frank