The 2026-08-18 metrics-storage outage exposed two defects in the
availability pipeline that distorted the figure in opposite directions at
once.
The Overview panel fell back to a live one-hour Traefik ratio whenever the
yearly rollup sample went stale for 48h, and rendered it under the same
"365d" title. When the rollup stopped publishing on 2026-08-18 the panel
quietly swapped a 365-day measurement for a 60-minute one and read 99.74%
instead of the recorded 99.95%. The fallback is removed: a stale rollup now
renders no value, and a new atlas-availability-rollup-stale alert pages at
26h, well before the panel goes blank at 48h.
The yearly ratio also silently excluded the 34-hour telemetry gap, because
missing days contribute zero requests and zero failures. Absent data was
read as "nothing happened" — had Atlas genuinely been down in that window,
the figure would still have said 99.95%. Availability keeps its
measured-days-only definition, which is correct, but coverage is now
published alongside it and shown in a new panel, so a telemetry gap lowers
disclosed coverage instead of vanishing. The title reads "365d window" to
stop implying 365 days of data exist; request-v4 begins 2026-05-01.
The rollup job reported healthy runs across a day and a half of lost
publishes: a read-only VictoriaMetrics accepts an import and discards it.
It now reads each sample back and fails loudly when the write did not
survive.
Not addressed here: availability is still measured from inside the platform
via Traefik counters, so it cannot distinguish "Atlas down" from "telemetry
down", and misses failures that never reach Traefik (DNS, TLS, node dead).
An external synthetic prober is the real fix and needs a hosting decision.
