A few years ago I already covered how to check the expiry date of a SSL certificate using OpenSSL. When the recent global outage of Windows Azure was caused by an expired SSL certificate, this got me thinking about this topic once again.
In my previous post, I presented a mechanism to check the remaining lifetime of an SSL certificate using the PEM certificate file locally on disk. However, in the case with Azure recently, customers were dependent on the actions by Microsoft and had no access to the actual file. Thus, there might be a need to check remote certificates of services you use, e.g. your off-site backup provider. As you want to ensure you can always use this service, why not check this for expiring certificates once in a while? Maybe it’s your notification to the sysadmins who saves yourself and all other customers from being locked out.
Here is the updated script ssl-cert-check that now not only handles x509 certificate files, but also remote addresses for various forms and protocols. For simplicity, here are the usage instruction from inside this script: