Data Flow — A Pod Crashes

This page traces a single pod crash through every stage of kwatch, from Kubernetes API watch to a chat message. Each step references the real package and function involved.

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Phase 1: Detection (Informer → Workqueue)

Pod transitions to CrashLoopBackOff
       │
       ▼
Pod informer (SharedInformer) receives ADD/UPDATE event
       │
       ▼
Event handler registered by controller.New() fires
       │
       ▼
enqueue.go: changeRecordingHandler / graph-aware pod handler update
the change tracker + dependency graph, then enqueue namespace/key
       │
       ▼
The pod's resourcePipeline workqueue receives "namespace/name"

The controller builds one resourcePipeline per watched kind (internal/controller/pipeline.go): a named rate-limited workqueue, informer sync state, a sync function, and a startWorkers gate. Each queue is independent — a slow deployment reconcile can't block a pod crash. Sync dispatch functions (sync.go) share one signature func (c *Controller) syncX(_ context.Context, key string) error.

Handlers also feed the two side structures the diagnostic engine needs:

• recordChange → context.ChangeTracker, so "what changed recently" has data;
• the graph-aware pod handler → context.ResourceGraph, so cause/impact analysis can walk the cluster's family tree.

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Phase 2: Filter Pipeline (Handler → Filter)

Worker goroutine picks up key from the pod queue
       │
       ▼
handler.ProcessPod() is called with the object
       │
       ▼
Builds filter.Context:
  • Sources   — client, config, listers, injected Now clock (read-only)
  • Pod/EvType/Owner/Events — the object under evaluation
  • Findings  — scratch area for detector conclusions
       │
       ▼
Detector chain (any returns StatusSkip → pod dropped)
       │
       ▼ (StatusContinue / StatusAlert)
Per-container evaluation (remaining detectors)
       │
       ▼
Enricher chain (fetch events, resolve owner, collect logs, check killing)
       │
       ▼
handler builds an event.Signal and calls correlation.Engine.Process()

The handler is the only place pod evaluation happens. Detectors write Findings (PodHasIssues, ContainerHasIssues, PodReason, and so on); enrichers fill in the incident's evidence and hint. Time-based decisions read the injected Sources.Now clock rather than the wall clock.

Key filters for a CrashLoopBackOff → OOM story:

• pod_status_filter.go — pod-level issues first;
• container_state_filter.go, container_reasons_filter.go — the container is terminated with reason OOMKilled;
• container_restarts_filter.go — the container is restarting (restart count increased since LastState);
• noise_filter.go — skips banal reasons (Normal, Scheduled, Pulled, Pulling); OOMKilled is not among them, so it passes;
• container_killing_filter.go, container_logs_filter.go, pod_events_filter.go, pod_owners_filter.go — enrichment.

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Phase 3: Correlation Engine (State & Dedup)

correlation.Engine.Process(ev, owner, containerState)
       │
       ▼
processLocked — every path through the same five stages:
       1) baseline      was it already broken at startup?      → quiet
       2) attribution   symptom of node / shared-dep / owner?  → counted, silent
       3) cooldown      resolved a moment ago?                 → silent revival
       4) identity      which incident is this?                → dedup / fold / escalate
       5) announcement  speak now?                             → group or edge
       │
       ▼
emit() → LifecycleHook(inc, action)
       │
       ▼
app.lifecycleHook: audit once → insight diagnosis → AlertManager.NotifyIncident()

Dedup key

Incidents are keyed by namespace:owner:reason:container (key.go BuildKey). Crash-looping reasons fold into one canonical key once restarts pass the threshold, so the incident's identity is stable across the container's momentary states. Image-pull failures with global scope (rate limits, registry timeouts, DNS, TLS) use a cluster-wide key.

Edge-triggered notification

// internal/correlation/engine.go
func notifSig(inc *model.Incident) string {
    st := "firing"
    if inc.State == model.StateResolved {
        st = "resolved"
    }
    return st + "|" + string(inc.Severity)
}

The signature "firing|critical" is compared against the incident's NotifiedSig. If unchanged, the action is ActionSkip — no duplicate alert on every poll. First sighting gives ActionCreate; later changes give ActionUpdate; the transition to resolved gives ActionResolved.

Severity resolution

The DefaultEnricher (wired in internal/app from severityByReason / severityByOwnerKind) resolves severity in order:

1. By reason — from severityByReason (defaults: Evicted, ImagePullBackOff → medium);
2. By owner kind — from severityByOwnerKind (default: StatefulSet → high);
3. Default — normal.

Severity is monotonic: once raised (including by escalation tiers), it never downgrades until the incident resolves.

Escalation check

// Default tiers: [3, 10]. Crossing the first raises severity to "high",
// crossing the second to "critical".
if cur >= e.config.EscalationTiers[i] {
    ev.Severity = severityForTier(i, inc.Severity)
}

7 restarts cross tier 0 (≥3), so severity escalates to high.

Node inhibition

When inhibition.nodeSuppressesPods is enabled and the pod's node has an active node-level incident, the pod is attributed to the node's alert — it is counted and listed, but not announced itself.

Smart grouping

If the event should speak but arrives inside the grouping window, it is buffered (grouping.go, group_flush.go). The window closes → one ActionUpdate notification summarizing the whole group on a stable group key, throttled by a 4×-window cooldown. If the OOM story was one pod, it is announced at the edge immediately.

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Phase 4: Insight (Cause / Impact / What-Changed)

The old "AI analysis" step never existed. In-process analysis replaces it:

LifecycleHook fires (action != skip)
       │
       ▼
app.lifecycleHook: opts.diagnose(inc, action)
       │   (no diagnosis for resolves or mass failures)
       ▼
insight.Engine.Analyze(inc) — walks the dependency graph
       │
       ├── cause.go     "node worker-2 may be unhealthy"
       │                 "owning Deployment orders-api is unhealthy"
       │                 "referenced ConfigMap may have changed"
       │                (else: walk backward to the deepest root)
       ├── impact.go    "5 pods, affecting 2 services"  (walk downstream)
       ├── changes.go   "Deployment dev/api updated 3m ago" (ChangeTracker)
       └── patterns.go  recognised signatures (repeating OOM, probes, image pulls)
       │
       ▼
Result travels with the notification as the 🧠 Diagnosis block

There is no external model, no sidecar container, and no enrichment channel — kwatch analyzes the incident with the graph it already maintains. If diagnoses come back empty on a large cluster, check kwatch_graph_nodes and kwatch_graph_edges on /metrics: an empty graph explains nothing.

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Phase 5: Alert Dispatch (NotifyIncident → Provider)

AlertManager.NotifyIncident(inc, action, insight)
       │
       ▼
Silence check ──── match? → DROP (silence.go, compiled silence index)
       │ no match
       ▼
fanOut: clone incident → one deliverJob per configured provider channel
       │ non-blocking
       ▼
Channel saturated? ──→ drop the arriving job, record dead-letter
       │ delivered (channel cap 256)
       ▼
Provider worker: deliverOne (delivery.go)
       ├── routes match? (routing.go) ── no match → Skip provider
       ├── buildMessage → ReportBuilder + provider renderer
       ├── truncate to provider byte limit
       ├── Send with retry classification (alert/util.Send):
       │     • 2xx        → success
       │     • 429        → ratelimit.Error; honour Retry-After (header or body)
       │     • other 4xx  → PermanentError → dead-letter immediately
       │     • 5xx / transport → retried with backoff
       └── all attempts failed?
           ├── fallback configured? → try the fallback provider
           └── else → dead-letter queue (ring buffer of 100, /deadletters)

Only retryable failures are retried. A malformed 4xx payload dead-letters immediately instead of delaying the alerts queued behind it. Provider delivery is through the shared alert/util.Send helper; the linter forbids raw net/http inside providers.

What the message looks like

Every notification is built from one provider-agnostic Report and rendered top-down:

🟠 Pod not ready — dev/api · Deployment · ContainersNotReady · high
pod stopped being ready 2m ago

🧠 Diagnosis
• Why: node ip-10-0-81-7 may be unhealthy (node_failure)
• Impact: affects service api
• Changed recently: deployment dev/api updated 3m ago

💡 check readiness probe and recent logs
  pod api-584ddc9849-gjwjp · image api:1.2.0 · node ip-10-0-81-7 · 2m · dev

🔍 Events — from api-584ddc9849-gjwjp
  Aug 25 23:52:21  FailedScheduling  0/5 nodes are available …

Report sections (internal/message/report.go) are populated selectively: headline, current state, diagnosis (hint + cause + impact + pattern), evidence (logs/events), recent changes, and type-specific sections (OOM timeline, probe endpoint, image-pull, scheduling delay). Renderers (slack_renderer.go, discord_renderer.go, plaintext_renderer.go, text_renderer.go) drop what they don't understand.

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Phase 6: Delivery & User Notification

Provider accepts the payload (HTTP 2xx)
       │
       ▼
Retry loop exits, breaker state resets
       │
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User sees the notification in #kwatch-alerts

The entire flow — from pod crash to chat message — completes in well under a second in normal operation. There is no AI stage and no sidecar round-trip: the diagnostic block is computed locally from the in-memory dependency graph.

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Summary: End-to-End in 8 Steps

#	Phase	Package
1	Informer detects pod change, enqueues key	internal/controller
2	Filter pipeline evaluates the pod	internal/handler + internal/filter
3	Correlation engine dedups and decides (five stages)	internal/correlation
4	Severity resolved, escalation applied	internal/correlation + internal/enricher
5	Insight diagnoses cause / impact / what-changed	internal/insight
6	Alert manager formats the report	internal/alert + internal/message
7	Provider retry / dispatch	internal/alert/* (via alert/util.Send)
8	User receives notification	the configured provider