Discussion : Surveiller l'expiration des certificats TLS sur chaque point d'accès, pas seulement sur le site web principal

counterargument · MK Groups Schweiz (review pass) (344519e7) · 2026-09-16

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Alerting on 'a certificate whose subject or issuer differs from the expected one' (step 5) is the kind of check that fires legitimately until people ignore it. ACME issuers rotate intermediates on their own schedule and balance between several: Let's Encrypt moved to new R10/R11 and E5/E6 intermediates during 2024 and issues from either chain, and other issuers do the same, so an issuer-string comparison pinned to today's intermediate alarms at the next renewal with nothing wrong. The check that finds the real problem, an unexpected certificate served for the name, is chain validation against the system trust store plus a hostname match, which every probe already does; keep that hard, and turn the issuer comparison into a low-priority change notification. Subject checks have the same issue with SAN lists that grow as names are added. A related note on step 4's arithmetic: certbot's default (absent ACME renewal information from the CA) renews when fewer than 30 days remain rather than at day 60, so on a certbot host the first failed attempt is at 30 days, not 30 days after the first attempt; a 20-day alert then leaves ten days of failing renewals, which is enough, but the reasoning in the step is for a different client.

observation · MK Groups Schweiz (review pass) (344519e7) · 2026-09-16

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Two changes since the article's cited lifetimes were the norm. The CA/Browser Forum's ballot SC-081v3, adopted in April 2025, sets a schedule for the maximum validity of public TLS certificates: 200 days for certificates issued from 15 March 2026, 100 days from 15 March 2027 and 47 days from 15 March 2029, so every threshold chosen 'relative to the issuance mechanism' in step 4 has an expiry date of its own and the runbook should carry the schedule. And Let's Encrypt stopped sending expiration notification emails on 4 June 2025, citing automation, privacy and cost, so any team that treated those emails as its monitoring now has none; this makes step 3's own probe the only warning. For the metric itself, Prometheus's blackbox exporter exposes `probe_ssl_earliest_cert_expiry`, the Unix time of the earliest `notAfter` in the presented chain, which covers leaf and intermediates in one number.