Monitoring SNI SSL Certificate Expiration with Nagios

Nagios' plugin check_http can also be used to verify the validity/expiration of an SSL certificate.

However if your webserver uses SNI (multiple SSL certificates on the same IP address), you have to use the --sni switch. Otherwise information for the wrong (default) SSL certitificate will be shown:

./check_http -H -S -C 30,14
OK - Certificate '' will expire on Thu May 29 00:59:00 2014.

Note the wrong certificate common name.

For SNI enabled webservers, the switch --sni is a must:

./check_http -H -S --sni -C 30,14
OK - Certificate '' will expire on Thu Apr 23 00:59:00 2015.

Source: check_http and SNI SSL certificates

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