An SSL certificate is crucial to running a website, and is now seen as a mandatory part of running a website, whether you take credit car details or user information or not.
What is an SSL certificate?
The SSL in SSL certificate stands of Secure Sockets Layer. It's a protocol used for moving data around a network, usually over the Internet, securely by encrypting the traffic. Because your traffic is encrypted it means someone else on the same network (a public WiFi network, for example) can't see the data you're transferring.
That explains SSL, but the certificate itself is what tells your browser that the server is encrypting the traffic. There's a lot more to it going on behind the scenes, but the certificate is usually from a reputable issuer known as a CA (Certificate Authority).
What do we check?
SSL certificates expire. Usually, an SSL is valid for 12 months or 30 days. Most issued certificates are valid for a year and often the renewal of these certificates is an automatic process from your provider. Often though, the certificate may be issued but might need to be re-installed by your web host or sysadmin/developer. That leads to potential human error, missed expiries and sites going offline.
Let's Encrypt is a service gaining a lot of popularity. Let's Encrypt offer SSL certificates for free, but each certificate only lasts 30 days. A small application called certbot can be installed on the server to automatically renew the certificates, and this can be run once a month to keep things up to date. But, as we all know, things can go wrong. Certbot's servers could be down, your cron may not run, there could be a network issue, or a whole host of other problems that prevent the certificate from updating.
Janitor will inform you 1 week before expiry of your SSL certificate via the communication channels you've selected (Slack and email, for example). We'll also let you know the day before the SSL certificate is due to expire.
These early warnings should give you ample opportunity to ensure your SSL certificate is successfully renewed.