Currently my production servers have PHP 5.5.1 installed and working fine.
PHP 5.5.1 (cli) (built: Jan 14 2014 11:37:09)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
However according to this post PHP has released 5.5.12 to fix some OpenSSL issues. We are running on CodeIgniter.
As I see there is no breaking change between 5.5.1 and 5.5.12, only bug fixes and few additions. So it should be fine to upgrade PHP version smoothly.
However recently we also upgraded to newer version of OpenSSL avoid heartbleed bug. So now is it necessary to upgrade the PHP for same reasons?
If I am not missing anything then upgrade won't cause any version related issue?
NOTE: As the post mentions the example of shared hosting/servers, we have our own multiple dedicated servers running behind load balancers.