How to get the expiry date of an HTTPS certificate with Ruby
Connect to the domain using net/http, then you can inspect the peer_cert/not_after property on the response.
I was tinkering with some HTTPS certificates, and I wanted to write a scheduled test that would check the certifcates weren’t about to expire. This is the sort of thing that should be handled by a good certificate provider – for example, Let’s Encrypt sends me emails when my certificates are close to expiry – but another check is a good belt-and-braces measure.
I did this with Python back in August, and I wanted to write similar checks in a codebase which is primarily Ruby. Fortunately Ruby’s net/http library exposes information about the HTTPS certificate, so it’s a bit simpler than in Python:
require 'net/http'
# Get the expiry date of the HTTPS certificate for this domain name
def get_cert_expiry(hostname)
uri = URI::HTTPS.build(host: hostname)
response = Net::HTTP.start(uri.host, uri.port, use_ssl: true)
cert = response.peer_cert
cert.not_after
end
puts get_cert_expiry("alexwlchan.net")
# 2025-02-17 08:34:57 UTC
The not_after property is a Time which can be used directly in datetime comparisons and calculations.