Production ran six weeks with a healthy process and a 0-byte log because
Serilog isolates per-sink failures: a file sink whose every write fails is
invisible from anywhere but SelfLog, which was not enabled. Two instruments:
- LogPipelineDiagnostics.EnableSelfLog (before the first logger builds):
SelfLog to logs/serilog-selflog.txt (rotated at 5 MB) + stderr — the only
channel that carries the exception the sink swallows.
- CheckFileSinkGrowth (after the startup banner): verifies each configured,
unbuffered file sink's rolled-file family physically grew across a marker
event; a silent sink is reported at boot via SelfLog/stderr and the
console sink instead of discovered months later. Growth-across-marker,
not existence — a previous run's bytes must not mask a silent sink (the
false pass an existence check would have given on wonder-app-vd03).
Never throws: both instruments swallow their own failures — a diagnostics
channel that can fail startup is worse than the defect it watches for.
The load-bearing test is the failure case (a sink that writes nothing IS
reported); a check that can only pass is indistinguishable from no check.
Joseph Doherty
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