Why does a data source connect but return no data?
A source passes its test but returns nothing: check write, store and query in turn — nothing written, time range past the last point, label mismatch, wrong store.
Why does a Categraf target show as offline?
A target shows offline when its heartbeat has not reached Redis in time — clock skew, a wrong heartbeat URL or network policy; update time is not a liveness signal.
Why does the alert not fire when the query returns results?
Query has data but nothing fires: the evaluation records hold the answer — for-duration not met, wrong datasource_queries, group or window mismatch, disabled, muted.
Why are evaluation records missing or dropped?
Missing evaluation records mean one of four things: not recorded, not evaluated, query rejected or cycle skipped; overload and datasource timeouts are the usual causes.
Why does an alert fire repeatedly or never recover?
Flapping or never-recovering alerts usually come from a threshold sitting on the data, a data gap read as recovery, a changing label set, or no recovery condition.
Why is there an alert event but no notification?
Event but no message: in the notification log, no record means a mute or notification rule stopped it; a failure points at the channel, a success at the receiver.
Why does notification template rendering fail?
A message body that is error text, or a field that is empty, is a template rendering problem that still logs as success; preview against a real event to catch it.
Why does the event pipeline route to the wrong destination?
Wrong recipients usually mean the destination was decided earlier than expected: processor order, a label rewrite before the match, or the two mount points' scopes.
Why does a workflow Try run succeed but production execution fail?
Try run passes, production fails: real events may lack labels the mock had, and the alert process — not the UI — runs the workflow with its own permissions and network.
Why is embedded TSDB data fragmented or missing?
Gaps in the embedded TSDB rarely raise errors — retention, disk pressure or restarts; three timestamp metrics show whether the gap is on the write or the query side.
Why does the edge lose contact with the center?
During a partition the edge keeps alerting locally but its events never reach the center — that is expected; an edge that never connected is a misconfiguration.
Why does MCP authentication fail?
MCP authentication fails at the gateway, the token check or OAuth — the status code says which; usual causes: wrong header name, expired token, bad redirect URL.
Why are MCP tools missing or denied?
"No such tool" has three shapes — write tools not enabled, toolset disabled, or the token's user lacks the permission — and the tools/list response tells them apart.
Why does an upgrade or database migration fail?
Unknown column errors, blank pages or a hung process after an upgrade mean the schema did not fully migrate — usually missing database privileges or an interrupted run.
Why is Nightingale slow or backlogged?
Late alerts, growing queues and high database CPU each map to one built-in metric that localises the cause; pick the metric by symptom, then work back to the root.