Renders services.opentelemetry-collector on the host: OTLP/HTTP receiver
on the bridge address, otlphttp exporter to otel.endpoint, and the
upstream credential delivered as EnvironmentFile so the collector
interpolates it at runtime and nix never sees the value.
Three things worth knowing, each measured rather than assumed:
- network.exposeHostPorts already exists and is wired (it opens the port
on the bridge interface only), so bridge reachability costs nothing.
- validateConfigFile defaults to isStorePath configFile, which is null on
the settings path - so upstream's default is OFF for exactly the way
this module configures it. Set true: it runs otelcol validate at build
time. It parses, it does not prove delivery.
- headersCredential's file is already NAME=value, i.e. EnvironmentFile
format, verified against a real settings.json rather than the doc.
An assertion refuses collector.enable with no headersCredential: the
collector exists to be the only holder of that token, and without one it
is indirection that reads as security.
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