Since you have to renew your certificates at least every 90 days and there’s currently no support for renewal in the official client, many users have resolved this issue by creating some wrapper script and putting that into cron. This may lead to problems, as cron may not be executed or something else.
It always should be best, if you monitor the state of your certificates in a periodic way too see if there’s a problem. This can be very easy if you have just one server (just connecting to the page once a day or week). But if you have multiple sites, you may want to have something more sophisticated. Maybe some standalone software or a plugin for one of the commonly used monitoring softwares (nagios, zabbix etc.)
I propose here a list of such monitoring software. Post your software below so that I can update this list accordingly.
I’ve created two open source tools to both monitor your certificate expiry and an ssl labs alternative, an ssl server test. Certificate expiry monitor is here: https://certificatemonitor.org/ and the ssl server test here: https://ssldecoder.org/
I use SSL Checker app and it has been quite handy for me to keep track of my expiring certificates. You may want to add it to your list to help other users. Thanks!