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docs: document datastore_connected and say what it actually reports - #2243
datastore_connected is not listed in docs/METRICS.md, the catalogue a reader goes to. #1843 touched eleven files and none of them was that one, so for most of this metric's life the only thing describing it has been its own HELP string: "Reports 1 if the datastore watcher has connected, 0 otherwise". (One line in docs/platform-connectors.md describes it correctly today, added in #2199 after the confusion below; the catalogue entry is still missing.) Ready has a single branch on provider == nil and never calls LagState(), and nothing restores the provider to nil (SetWatcher(nil) returns early), so the gauge is 1 from the moment the watcher starts and stays there for the life of the process.
The behaviour is right. A watcher that stops after connecting is surfaced by the component exiting — node-drainer/main.go:298 (whose comment reads "Signal a critical failure so the pod exits and Kubernetes restarts it"), fault-remediation/main.go:281, fault-quarantine/pkg/eventwatcher/event_watcher.go:168 — which is the path #2020, #2024 and #2040 established, and which change_stream_reopens_total's own row in METRICS.md already describes. The gauge simply is not the thing that reports it.
Read as written, the HELP invites an alert on datastore_connected == 0. That alert cannot fire. We wrote one against a fleet, kept it, and found it inert only on reading Ready — having first spent a while looking for a pipeline fault, because a gauge that promises connectivity and never drops looks like a gauge whose consumer is broken.
It is the readiness probe, in gauge form
Worth saying in the catalogue because it changes what an operator should alert on. WithReadinessCheck takes a single checker and /readyz is 503 exactly when that checker errors (commons/pkg/server/server.go:301). All three components register this checker and nothing else — server.WithReadinessCheck(readinessChecker) in node-drainer/main.go and fault-quarantine/main.go, mgr.AddReadyzCheck("readyz", readinessChecker.Check) in fault-remediation/main.go — and the charts point readinessProbe.httpGet.path at /readyz.
So kube_pod_status_ready already carries the same answer, with pod and namespace labels, and it still answers when the metrics endpoint itself is down — the case where this gauge is absent rather than 0. #1839 asked for the gauge so that alerting would not have to poll probes, but it never had to: kube-state-metrics exports readiness already.
That does not make the gauge wrong to have — it comes from the component's own registry, so it works without kube-state-metrics — but it is not independent information, and the catalogue row now says so rather than leaving a reader to discover it.
Two changes:
docs/METRICS.md gains a row for it, in the Change Stream Metrics table alongside the siblings it belongs with, plus a note on the section preamble since this one comes from commons/pkg/server rather than store-client and carries no client label. The row says it latches, points at kube_pod_container_status_restarts_total for the case the gauge cannot show, and recommends kube_pod_status_ready over it for the case it can.
commons/pkg/server/datastore_readiness.go gets three statements corrected: the HELP, the type doc ("reports readiness based on change stream watcher lag state"), and the setter doc ("the LagStateProvider used to determine datastore connectivity"). The setter's new comment says Ready does not call LagState, so the next person to work on this does not assume the lag check is already wired.
Not in this PR: the name. connected reads as "currently attached" and the gauge means "started once", which no comment fully repairs. change_stream_watcher_started would put it in the family its siblings occupy, and started avoids colliding with the readiness probe this checker also serves. A rename is cheaper than it looks — the metric has no METRICS.md entry today and no labels, so there is no documented surface or series shape to migrate — but it still breaks anyone who built on the name, so it wants deciding on its own. The new METRICS.md row records the mismatch so the question does not get lost.
Type of Change
🐛 Bug fix
✨ New feature
💥 Breaking change
📚 Documentation
🔧 Refactoring
🔨 Build/CI
Component(s) Affected
Health Monitor
Core Service
Fault Management
Janitor
Deployment/Config
API/Interface
Preflight
Plugins
Documentation/CI
New Component
Multiple Components
Other
Testing
Tests pass locally
Manual testing completed
No breaking changes (or documented)
Tests pass locally — go test ./... -count=1 across commons exits 0: 21 packages ok, no failures, 5 with no test files. This module needs no envtest, so unlike most of this repository the suite covering the changed file actually ran here, commons/pkg/server included. gofmt, go build ./... and go vet ./pkg/server/ are clean.
Manual testing completed — every statement was checked against the code or measured, not inferred from how it ought to work:
Ready's single branch, the absence of any LagState() call in that file, and SetWatcher(nil) returning early;
the three exit guards cited above, read in each component;
min_over_time(datastore_connected[30d]) == 1 on a live v1.29.0 install, across six pod lifetimes — two generations each of fault-quarantine, node-drainer and fault-remediation, so the window includes startups, with no gap in count_over_time;
that WithReadinessCheck holds one checker and that each of the three components registers only this one, which is what makes the gauge equivalent to pod readiness.
No breaking changes — comments, a HELP string and a documentation table. The HELP text is longer, which changes one # HELP line in /metrics output and nothing else.
Checklist
Self-review completed
Documentation updated (if needed)
Ready for review
AI assistance was used for this change. Worth knowing where to look closely: the first version of this report claimed the gauge's inability to reach 0 left datastore loss undetected, and re-reading main found the exit guards in all three components, so that claim was wrong and the scope is documentation only. The first version of the HELP text was also written in implementation terms ("has been assigned") before being rewritten for the operator who meets this metric in a dashboard.
Summary by CodeRabbit
Documentation
Clarified that datastore readiness becomes successful when the change-stream watcher is handed to the readiness checker, before its event loop starts, and does not reflect watcher lag.
Documented that datastore_connected remains at 1 if the datastore is later lost; the component stops and the pod restarts.
Specified which components expose the metric, noted that it has no client label, and recommended kube_pod_status_ready unless a component-specific signal is needed.
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Walkthrough
The change clarifies that readiness reflects whether the change-stream watcher has been handed to the checker. It documents the datastore_connected gauge’s source, label set, and latched value after handoff.
Changes: Datastore readiness documentation
Layer / File(s)
Summary
Readiness and metric contract commons/pkg/server/datastore_readiness.go, docs/METRICS.md
The checker documentation states that readiness checks whether a provider is set and does not call LagState. The metric documentation describes the gauge’s value before and after watcher handoff, its source and lack of a client label, and its role as the full readiness check for the named components.
NVIDIA/NVSentinel#2159: Changes the readiness checker and watcher contract that this PR documents.
NVIDIA/NVSentinel#2199: Documents liveness metrics and identifies datastore_connected, which this PR describes in more detail.
Suggested labels:area/docs, area/core, size/S
Suggested reviewers:hesandaliyanage, lalitadithya
Merge Risk: Minimal · previous review 876ed
The documentation matches the checked readiness and metric behavior. No actionable merge risk remains after normal checks.
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The title clearly and concisely describes the main changes: documenting the datastore_connected metric and clarifying what it reports.
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Reviewing files that changed from the base of the PR and between 2c9936a and 876ed28.
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commons/pkg/server/datastore_readiness.go
docs/METRICS.md
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commons/pkg/server/datastore_readiness.go
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Inline comments:
Review comments at @commons/pkg/server/datastore_readiness.go:
- Line 37: Update the DatastoreReadinessChecker comment and the related metric
help text and METRICS documentation to describe readiness as the watcher
provider being constructed and handed to the checker via SetWatcher, which is
when Ready succeeds. Do not describe readiness as watcher startup or imply that
handoffs without a LagStateProvider count.
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Reviewing files that changed from the base of the PR and between 07d2b2b and 2c9936a.
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commons/pkg/server/datastore_readiness.go
docs/METRICS.md
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Summary
datastore_connectedis not listed indocs/METRICS.md, the catalogue a reader goes to. #1843 touched eleven files and none of them was that one, so for most of this metric's life the only thing describing it has been its own HELP string: "Reports 1 if the datastore watcher has connected, 0 otherwise". (One line indocs/platform-connectors.mddescribes it correctly today, added in #2199 after the confusion below; the catalogue entry is still missing.)Readyhas a single branch onprovider == niland never callsLagState(), and nothing restores the provider to nil (SetWatcher(nil)returns early), so the gauge is 1 from the moment the watcher starts and stays there for the life of the process.The behaviour is right. A watcher that stops after connecting is surfaced by the component exiting —
node-drainer/main.go:298(whose comment reads "Signal a critical failure so the pod exits and Kubernetes restarts it"),fault-remediation/main.go:281,fault-quarantine/pkg/eventwatcher/event_watcher.go:168— which is the path #2020, #2024 and #2040 established, and whichchange_stream_reopens_total's own row inMETRICS.mdalready describes. The gauge simply is not the thing that reports it.Read as written, the HELP invites an alert on
datastore_connected == 0. That alert cannot fire. We wrote one against a fleet, kept it, and found it inert only on readingReady— having first spent a while looking for a pipeline fault, because a gauge that promises connectivity and never drops looks like a gauge whose consumer is broken.It is the readiness probe, in gauge form
Worth saying in the catalogue because it changes what an operator should alert on.
WithReadinessChecktakes a single checker and/readyzis 503 exactly when that checker errors (commons/pkg/server/server.go:301). All three components register this checker and nothing else —server.WithReadinessCheck(readinessChecker)innode-drainer/main.goandfault-quarantine/main.go,mgr.AddReadyzCheck("readyz", readinessChecker.Check)infault-remediation/main.go— and the charts pointreadinessProbe.httpGet.pathat/readyz.So
kube_pod_status_readyalready carries the same answer, with pod and namespace labels, and it still answers when the metrics endpoint itself is down — the case where this gauge is absent rather than 0. #1839 asked for the gauge so that alerting would not have to poll probes, but it never had to: kube-state-metrics exports readiness already.That does not make the gauge wrong to have — it comes from the component's own registry, so it works without kube-state-metrics — but it is not independent information, and the catalogue row now says so rather than leaving a reader to discover it.
Two changes:
docs/METRICS.mdgains a row for it, in the Change Stream Metrics table alongside the siblings it belongs with, plus a note on the section preamble since this one comes fromcommons/pkg/serverrather thanstore-clientand carries noclientlabel. The row says it latches, points atkube_pod_container_status_restarts_totalfor the case the gauge cannot show, and recommendskube_pod_status_readyover it for the case it can.commons/pkg/server/datastore_readiness.gogets three statements corrected: the HELP, the type doc ("reports readiness based on change stream watcher lag state"), and the setter doc ("the LagStateProvider used to determine datastore connectivity"). The setter's new comment saysReadydoes not callLagState, so the next person to work on this does not assume the lag check is already wired.Not in this PR: the name.
connectedreads as "currently attached" and the gauge means "started once", which no comment fully repairs.change_stream_watcher_startedwould put it in the family its siblings occupy, andstartedavoids colliding with the readiness probe this checker also serves. A rename is cheaper than it looks — the metric has noMETRICS.mdentry today and no labels, so there is no documented surface or series shape to migrate — but it still breaks anyone who built on the name, so it wants deciding on its own. The newMETRICS.mdrow records the mismatch so the question does not get lost.Type of Change
Component(s) Affected
Testing
Tests pass locally —
go test ./... -count=1acrosscommonsexits 0: 21 packagesok, no failures, 5 with no test files. This module needs noenvtest, so unlike most of this repository the suite covering the changed file actually ran here,commons/pkg/serverincluded.gofmt,go build ./...andgo vet ./pkg/server/are clean.Manual testing completed — every statement was checked against the code or measured, not inferred from how it ought to work:
Ready's single branch, the absence of anyLagState()call in that file, andSetWatcher(nil)returning early;min_over_time(datastore_connected[30d]) == 1on a live v1.29.0 install, across six pod lifetimes — two generations each offault-quarantine,node-drainerandfault-remediation, so the window includes startups, with no gap incount_over_time;docs/METRICS.mdhas no entry for it, and that fix(fault-management): report datastore connectivity in readiness probes #1843's eleven changed files do not include it, which is what left the HELP carrying the description on its own;WithReadinessCheckholds one checker and that each of the three components registers only this one, which is what makes the gauge equivalent to pod readiness.No breaking changes — comments, a HELP string and a documentation table. The HELP text is longer, which changes one
# HELPline in/metricsoutput and nothing else.Checklist
AI assistance was used for this change. Worth knowing where to look closely: the first version of this report claimed the gauge's inability to reach 0 left datastore loss undetected, and re-reading
mainfound the exit guards in all three components, so that claim was wrong and the scope is documentation only. The first version of the HELP text was also written in implementation terms ("has been assigned") before being rewritten for the operator who meets this metric in a dashboard.Summary by CodeRabbit
datastore_connectedremains at1if the datastore is later lost; the component stops and the pod restarts.clientlabel, and recommendedkube_pod_status_readyunless a component-specific signal is needed.