df96be98bff26648157db86dce33d42e53f85fe2
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Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
  jakman85andClaude Opus 5
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79d9ab2c8c |
feat(monitoring): per-export NFS latency alerts — server-slow vs we-are-backed-up
Closes the gap `feat/io-pressure-diagnostic-context` deliberately left open. That
change enabled node-exporter's `--collector.mountstats` and recorded its own honest
limit: "an NFS export that is merely SLOW cannot be distinguished today", because
node_mountstats_* did not exist on prod until the HelmRelease rolled and the L0 guard
alert-metrics-have-scrape-targets rightly refuses a rule on an unscraped metric.
The rollout has landed. Verified on prod 2026-09-15: 1,842 node_mountstats_* series
(~0.4% of a 451,650-series head), six mounts, 426 per-operation series in each of the
five operation families and 6 in each transport family. Every metric referenced below
returns series under `promtool query instant`.
FIVE RULES in platform-health.node-io-cause, each naming its cause in `summary`:
NFSExportServerSlow response_time > 50 ms/op, our op rate > 20/s,
queue_time < 5 ms/op -> the server is slow BECAUSE OF US
NFSExportServerSlowNotOurLoad same, but our op rate 1-20/s -> the server is slow and
the load is NOT OURS. This is the operator's Proxmox
hypothesis made testable.
NFSClientQueueTimeHigh queue_time > 5 ms/op -> WE are saturating the transport
NFSTransportBacklogDeep backlog depth > 8 per send -> even the grown slot table is full
NFSExportMajorTimeouts any major timeout in 15m -> the export is HANGING (critical)
THE DISCRIMINATOR. mountstats splits a slow NFS op into the half the server owns
(response_time) and the half we own (queue_time). High response with low queue means the
SERVER; high queue means US. The two server rules then partition that state by our own op
rate at 20/s, so exactly one of them can fire and it names which reading applies. The
`unless queue_time > 5ms` clause is what licenses reading response_time as a statement
about 192.168.2.102 rather than about us, and it is pinned by fixture 5 (a client queueing
30 ms/op while the server appears to take 60 ms/op: both server rules must stay quiet).
MEASURED BASELINE, prod 2026-09-15, re-measured for this change:
server response time 4.40-4.81 ms/op (30m window), uniform across all six mounts
client queue time 0.013-0.067 ms/op; snapshot maximum 0.333 ms/op
our own op rate 0.019-0.163 ops/s — STATFS keepalive and nothing else
major timeouts 0 on every mount
backlog depth 0 on every mount
slot-table high-water 586 (prod-1), 162 (prod-3), 2 (prod-2)
THREE LIMITS ON THAT BASELINE, recorded in the rules and the runbook rather than papered
over:
(a) the history is MINUTES, not days — the series begin when the DaemonSet rolled
(count_over_time(...[24h]) returned 18, and time() - process_start_time_seconds read
558-561 s on all three nodes), so no rule uses a range longer than 15m;
(b) it is an IDLE baseline — STATFS keepalive only, no READ/WRITE traffic, so the 50 ms
threshold is argued from the link and the array (one outstanding 1 MB read at 50 ms is
20 MB/s) and must be re-cut after the first real media event. The runbook carries the
query;
(c) prod-1's /mnt/Storage/plex and /mnt/Storage/plex/downloads report byte-identical
per-operation counters (0.12443893333333335 on both, to every digit), as do prod-3's two
nextcloud mounts — mounts sharing one NFS superblock share the kernel's RPC statistics.
One slow export on prod-1 therefore raises two alerts. Documented, not aggregated away.
PROOF, not assertion. platform/monitoring/tests/nfs-export-latency.test.yaml: seven fixtures
(measured healthy; healthy under 60 ops/s of real load; server-slow-ours; server-slow-not-ours;
client-backed-up; backlog-deep; export-failing), and every fixture asserts all five alertnames
in the fires or the quiet direction. The measured baseline is pinned as a band, the
shared-superblock duplication is pinned, and both hazards the sibling recorded are asserted:
the PromQL precedence trap (`(ratio) and rate(ops) > 1 > 0.050` returns a series on a healthy
60 ops/s mount; the shipped form returns none) and the op-rate guards (a mount doing half an
operation a second at 1 s/op response, 1 s/op queue and 20 deep in the backlog — 20x, 200x and
2.5x the three thresholds — must stay silent).
MUTATION-CHECKED, 14 mutations, every one of them making the test file FAIL: each of the five
thresholds moved in both directions where the fixtures allow it, both `unless` clauses deleted,
and all four rate guards loosened. The two clause deletions fail with an exp/got alert diff,
not a parse error. No threshold here is pinned only by a promql_expr_test restating it.
Live on prod, all five shipped expressions return NO series while all four of their
sub-expressions return six each — so the silence is a verdict, not missing data.
runbooks/node-io.md: the triage table grows from 10 rows to 15 (per-export server response
time, client queue time, our own demand, major timeouts, backlog depth), with real measured
HEALTHY values and an explicit "not collected" in both incident columns, because the collector
postdates both events and that can never be backfilled. A new four-way verdict table reads rows
11-13 together and maps each combination to the alert that says it.
HONEST REMAINING GAP: these rules rule US out; they cannot rule Proxmox IN. The per-client view
of an export exists only on the server. What would settle it is one read on 192.168.2.102 while
NFSExportServerSlowNotOurLoad is firing — `nfsstat -s` and /proc/fs/nfsd/clients/*/info — which
is out of scope from this repo. Recorded in the runbook.
Co-Authored-By: Claude Opus 5 <[email protected]>
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