How to monitor a website and SSL expiry

An expired SSL certificate scares visitors with security warnings, and a down site means lost customers. Both can be monitored automatically.

Availability monitoring

Uptime Kuma periodically checks whether the site responds and alerts you on downtime, see uptime monitoring.

SSL monitoring

Uptime Kuma can also alert when an SSL certificate is close to expiring (for example 14 days ahead). That gives you time to renew.

Manual SSL check

echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -noout -dates

Automatic renewal

Let's Encrypt certificates renew automatically through Certbot, if the timer runs, see free SSL certificate. Monitoring stays a safety net in case renewal fails.

Check the content, not just the code

A site can return code 200 but display an error. Configure the monitor to look for a keyword from the page, so you catch this kind of problem too.