How to Monitor SSL Certificate Expiry (Before Your Users Notice)

An expired TLS certificate is the worst kind of outage: total, instant and loudly announced by your users' browsers. Unlike a down server it often happens on a Saturday, weeks after someone forgot to flip an auto-renewal setting. The fix is boring and reliable: monitor the expiry date and page a human while there is still time.

What a certificate monitor should check

• Days until expiry — the single most important number. Alert at 30, 14 and 7 days.
• Issuer changes — a re-issued certificate from an unexpected CA is worth a look.
• Hostname coverage — SAN mismatches break clients even when the chain is valid.
• Chain completeness — missing intermediates fail on some mobile clients only.

Why renewal scripts are not enough

Auto-renewal (ACME/Let's Encrypt) works — until it doesn't: DNS propagation delays, port-80 blocks, rate limits or a changed web server config. Independent expiry monitoring is the safety net that assumes renewal may fail.

Setting it up with SiteFlux

Add an SSL monitor for your domain, pick your alert channels — email, SMS, Telegram or a phone call for the last warning — and you're done. SiteFlux re-checks the certificate on every cycle and records its history, so you can also see when a renewal actually happened.