A local time-series database rather than only an external sink, so the
swarm dashboard stays readable when the outside world is not: a view of
the system must not depend on the system it views being healthy.
listenAddress is pinned to loopback. Upstream defaults it to every
interface, and the OTLP ingest path this exists to receive on is
unauthenticated — the gateway is the only intended client and it is on
this host, so a wider bind would publish a write endpoint to whatever
the host is reachable on.
retentionPeriod defaults high rather than being required, because the
two failure directions are not symmetric: too long fills a disk, which
is visible and recoverable by lowering it, while too short destroys
history silently and permanently. The operator lowers it once they have
measured how fast this swarm accumulates.
OTLP needs no flag. Measured against the pinned 1.146.0 rather than
inferred from the module's option list, which has no OTLP switch and so
reads as though the feature were missing: the running server answers
POST /opentelemetry/api/v1/push with 200, where a nonexistent path
answers 400.
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