How to Monitor SSL Certificate Expiration

Step 1: Inventory every certificate

You cannot monitor what you haven't listed. Walk every source: production domains, staging hosts, marketing microsites, API gateways, load balancers, CDN edges, internal tools with public certs, and every subdomain. Forgotten subdomains cause most SSL outages — the main site renews fine while legacy-api.example.com dies quietly.

Step 2: Check daily, tighten near expiry

Daily expiry + chain checks are the baseline. As a certificate approaches expiry, cadence should tighten automatically — a renewal failure 3 days out needs hourly attention, not tomorrow's daily run. With lifetimes shrinking toward 47 days, weekly-or-slower schedules leave zero recovery margin.

Step 3: Use staged alert thresholds

One alert at 7 days is a pager fire; five staged alerts are a process. The ladder that works: 60 → 30 → 14 → 7 → 1 days. Early rungs go to chat/email for planned work; late rungs page on-call. Every alert must carry the facts: domain, days remaining, issuer, and what changed since last check.

Step 4: Validate more than the date

• Full chain: expired intermediates and missing chain certs break mobile clients while desktop looks fine.
• Change detection: issuer or SAN changes without a planned renewal are compromise signals — alert on the diff, not just the date.
• CT logs: watch for certificates issued for your domains that you didn't request (see Certificate Transparency monitoring).

Build vs. buy in one paragraph

A cron + OpenSSL script covers one server until it doesn't: multi-endpoint validation, alert routing, CT watching, and dashboarding are where DIY dies. A service earns its keep the first time a renewal fails silently at 2am. Certack runs daily SSL and DNS checks with the 60/30/14/7/1-day ladder on 9 channels — two sites free, set up in 30 seconds.