Define freshness at review time
At synthetic minute 20, monitor marks heartbeat current if last received age≤5 minutes. A last received 15, B at 14, C none. A stale or absent heartbeat means observation unknown; it does not by itself prove the application is down. No transport diagnosis is supplied.
| Service | Last minute /age | State |
|---|---|---|
| A | 15 /5 | Current |
| B | 14 /6 | Unknown |
| C | None /not computable | Unknown |
Calculate last-observation ages
- Use a common review instant
- Calculate age only where timestamp exists
- Classify current or unknown
Do not convert absent timestamps to zero age.
How many services have current heartbeat evidence?
Show the worked answer
One, A; B andC are unknown. None is established as failed by this heartbeat-only worksheet.
Name unknown status precisely
| Case | Decision | Reason |
|---|---|---|
| Age exactly 5 | Current | Inclusive≤5 rule |
| No heartbeat | Unknown | No received observation |
Use a separate application observation to resolve service state and an observation-path check to investigate missing data. Retain those two questions separately.