In my post two weeks about setting consistent headers in nginx, one of the headers I was concerned with was the Public Key Pinning header (HPKP). This, and the Strict Transport Security header (HSTS) are both defensive mechanisms meant to increase the reliability of secure connections to a given site.
As noted previously, I’ve opted to serve all of my sites securely. I even went to far as to get ethitter.com on Chrome’s preload list, meaning no major browser even attempts an insecure connection to my site. Try loading http://ethitter.com/ in Chrome, Firefox, or Safari, and the browser will redirect to https://ethitter.com/ before my nginx configuration ever tells it to.
That vaguely-entertaining detail aside, this means that I’ve reason to be concerned about how soon my SSL certificates expire. The HPKP headers I set have 60-day lives, which I need to account for any time I renew the certificate for a pinned domain.