bao's metrics were scraped by the SWARM collector over loopback, via a
`swarm.otel.scrapeTargets.bao` entry gated on `deploy.swarm-otel.enable`
— "does the swarm's collector run on THIS host". It had to be: loopback
only reaches a reader that landed on the same host.
What that rendered everywhere else was nothing at all. Off that host the
metrics listener was not emitted, so the store's metrics reached the
store nowhere, and a host with no entry is indistinguishable from a host
nobody asked to scrape.
Moves the scrape into the collector this container already runs, per
mara on #4537: "move the existing scraper to the local collector". The
container shares the host netns (privateNetwork = false), so the scrape
still dials 127.0.0.1 — the listener keeps its address, its
`metrics_only` narrowing and its loopback-only bind, and the API
listener's `tls_require_and_verify_client_cert` is untouched.
The listener and its `prometheus_retention_time` lose their gate: the
reader ships with the store now, so there is no host where the endpoint
has none. The metrics pipeline reuses the logs pipeline's `resource`
processor and `otlphttp` exporter, so both signals carry the same
`service.name` and leave by the one hop.
Logs are unaffected: `journaldUnits` and --link-journal=host stay until
every sibling swarm container has a collector of its own.
The module-eval absence arm "a store with no collector beside it serves
no metrics" is inverted rather than dropped — the condition it asserted
is the bug. Three cases join it: the job is in swarm-bao AND gone from
swarm-otel (a move, not a copy), the scrape target and listener are both
pinned to loopback, and the metrics pipeline shares its exporter with
the logs one.
The single module-eval derivation forced ~62 full nixosSystem
fixtures live at once to compute its cases list: 10.6GB peak RSS /
5m25s to evaluate, by far the dominant cost in nix flake check.
Splits it into 21 independent checks.module-eval-* derivations
(1-7 fixtures each) sharing builders/helpers via module-eval/lib.nix,
so no single derivation needs more than a handful of fixtures live
at once. A few cases spanning two clusters carry a small duplicated
fixture rather than threading shared state through lib.nix.
