feat: expose assault metrics via Micrometer/Prometheus (#46) - #51
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Add an optional quarkus-goblin-metrics module that surfaces the assault activity as Micrometer metrics on any backend: - new AssaultObserver SPI on the engine, notified on every recorded assault and on every active-state change (observers errors are never propagated); reused later by the OpenTelemetry and assertion work. - GoblinMetricsObserver bean registers goblin_active (functional gauge), goblin_assaults_total (counter, tags type+source) and goblin_latency_injected_seconds (latency histogram, tag source). - source tag derived from the history identifier: server, rest-client, webclient. Documentation: new metrics page, README sections, compatibility note and roadmap tick; integration tests cover the live Prometheus scrape.
Add dedicated engine unit tests showing that an observer throwing on notification never breaks recordAssault or setActive, and that healthy observers still receive their notifications alongside failing ones. Also clarify in the metrics docs that Micrometer names keep dots while the Prometheus export sanitizes them to underscores.
ErwanLT
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September 22, 2026 06:45
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Closes #46
Optional
quarkus-goblin-metricsmodule exposing the assault activity as Micrometer metrics.What's included
AssaultObserverSPI on the engine, notified on every recorded assault and on every active-state change. Observer failures are caught and never alter the request path — reused later by the OpenTelemetry (feat: OpenTelemetry tracing integration #47) and post-assault assertions (feat: post-assault assertions (resilience verification) #50) work.GoblinMetricsObserverbean registering:goblin_active— functional gauge overengine.isActive()(1/0),goblin_assaults_total— counter taggedtype+source(server,rest-client,webclient),goblin_latency_injected_seconds— latency histogram taggedsource(p99/min/max derivable from the_bucketseries).sourceis derived from the history identifier.PT1Sstep).metricspage, README sections, compatibility note, roadmap tick.Notes
quarkus-micrometer-registry-prometheusbecausequarkus-micrometeralone does not provide a backend._maxis interval-based by design (likehttp_server_requests_seconds_max); documented in the metrics page.Build verified:
./mvnw clean verify(runtime · runtime-dev · metrics · integration-tests · docs), formatter clean.