Letsencrypt is a wonderful, simple and cost free way to encrypt your SSL traffic.
Since it start it helped protect data privacy to millions of websites. One of the downsides of Letsencrypt is the limited time a certificate is valid. Every three months you need to update your certificates, otherwise your users will be seeing a warning page in their browsers.
But not only Letsencrypt users struggle with the problem of expiring certificates. Also bigger every now and then face the same problem. Just with a different twist. The more servers and components are running SSL and need certificates, the more likely people tend to buy certificates with long running periods. Which means, on one hand you have to touch all these systems only every couple of years, but on the other hand the probability that the colleague that installed the cert is not around anymore. Results in partial failing systems and people under pressure trying to fix system by system.
As I am running multiple servers and also multiple domains, I created a small Python script called SSLChecker which notifies you via email 30,14,3 and one day before a certificate expires.
It can handle multiple domains at once and notify a list of people.
It is under the GNU license released on GitHub. Feel free to contribute, use and help keeping data private.