Multi-target collection with optional OTLP

Status

Accepted — family-novel. Optional OTLP loop implemented in Phase 4.

Context

The family reference architecture is a snapshot model: a background loop polls one appliance on an interval, swaps an immutable snapshot, and both /metrics and an OTLP push read it. idrac_exporter is different: it is a multi-target exporter scraped as /metrics?target=<bmc> (the idiomatic Prometheus relabel pattern, like snmp_exporter and blackbox_exporter). BMC scrapes can take minutes, so a single fleet-wide poll loop on a fixed interval is operationally worse than letting Prometheus parallelize per target.

Decision

Keep the on-demand ?target= path as the primary collection model (per-target collector cache with concurrent-scrape coalescing). Add an optional, off-by-default background snapshot loop that polls only the configured hosts: and OTLP-pushes them. This is a new "multi-target exporter" class that the family architecture.md is updated to recognize.

Consequences

Two collection paths to maintain. On-demand is never removed, so the relabel pattern and the /discover endpoint keep working. OTLP is available for environments that want push, without forcing a fleet-wide poll cadence. The snapshot loop reuses the existing collector rather than reimplementing it.