feat(metrics): one endpoint for the whole container (#135) - #136
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… merge + local-exporter federation (#135) A php-baseimages container had grown three Prometheus endpoints: 9090 (cbox_init_*), 9110 (fpm_tune_*, embedded engine with its own listener) and 9114 (fpm-exporter). The scale-out signal was literally split across ports. The main /metrics response can now carry the whole story: - Embedded engines merge natively: the runtime autotuner's registry is added to the main endpoint's gatherers when the tuner starts (it starts after the metrics server, so gatherers are snapshotted per scrape under a lock). fpm_tune.metrics_addr stays optional for standalone parity. - global.metrics_federate declares local exporters whose exposition is appended to every scrape: per-source timeout (2s) and TTL cache (5s), 8 MiB body cap, OpenMetrics EOF terminators stripped. Each source contributes cbox_init_federate_up{name}; a down source degrades to 0 and drops its stale body rather than failing the scrape or serving old data as current. - URLs are validated to loopback only (127/8, ::1, localhost) - the metrics port must not become a proxy for whatever a config points at. - With federation enabled the endpoint serves the plain-text exposition unconditionally, since federated bodies are appended verbatim and must not disagree with a negotiated encoding. Verified: unit tests for federation (up/down/TTL/EOF/size-cap) and the merged handler; config validation tests (loopback enforcement, duplicate names); full gate green (coverage 81% over the 78% floor, govulncheck clean, SBOM regenerated for the two now-direct prometheus deps); and an end-to-end run of the built binary - one scrape returned own series + federated body + federate_up 1, and killing the source degraded to 0 with the scrape still 200.
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Implements #135 in full - see the commit message for design and verification details.
One scrape, one story:
metrics_addrstays optional)global.metrics_federate: loopback-only local exporters appended per scrape, TTL-cached, degrading tocbox_init_federate_up 0when downmetrics-federate.yaml)php-baseimages will collapse its documented three-port layout to this single endpoint once released.