ANA-7386 Add Protorabbit instrumentor

[markcmurphy]

Jira: ANA-7386

What/Why?

Protorabbit processes have no Prometheus instrumentor, so the exporter server never starts and any metrics pushed during message processing fail with Errno::ECONNREFUSED. This is confirmed in theme-registry, auth, bmp, and bigpay, so the fix lives here rather than in each service individually.

Changes:

• lib/bigcommerce/prometheus/instrumentors/protorabbit.rb — new Protorabbit instrumentor; starts the exporter server, registers the built-in ActiveRecordCollector/ActiveRecordSql type collector, then any configured protorabbit_collectors/protorabbit_type_collectors, mirroring Hutch/Resque minus middleware setup
• lib/bigcommerce/prometheus/configuration.rb — adds protorabbit_collectors/protorabbit_type_collectors config, defaulting to []
• lib/bigcommerce/prometheus.rb — requires the new instrumentor
• README.md — documents Protorabbit.new.start usage and the new config keys
• CHANGELOG.md, version.rb — bump to 0.9.0

A few notes for reviewers:

• Protorabbit has no tracer/middleware hook like Hutch does, so this instrumentor only starts the server and registers collectors — it doesn't wrap message processing itself. It unblocks metrics (e.g. gRPC client interceptor metrics) already being pushed from inside message handlers that were previously refused for lack of a listening exporter.
• Protorabbit.new takes no app: arg, unlike Hutch.new(app:) — there's no Rails app object available in a protorabbit worker context.

Rollout/Rollback

Ships as a new gem version (0.9.0) with no behavior change until a consuming service calls Bigcommerce::Prometheus::Instrumentors::Protorabbit.new.start in its protorabbit boot code. Existing Web/Resque/Hutch instrumentation is untouched.

Rollback is a plain gem downgrade; no data or schema is involved. Consuming services (theme-registry, auth, bmp, bigpay) need a follow-up change to actually wire in .start — that adoption is out of scope here.

Testing

Automated:

• spec/bigcommerce/prometheus/instrumentors/protorabbit_spec.rb — covers disabled-noop, enabled start (registers ActiveRecordCollector, registers the ActiveRecord SQL type collector, registers configured type collector last so it can override, starts server, starts collectors), and rescue-and-log on server start failure

bundle exec rspec spec/bigcommerce/prometheus/instrumentors/protorabbit_spec.rb

Manual verification:

Before fix (no .start call) — reproduces the exact bug from ANA-7386:

W, [...] WARN -- : [bigcommerce-prometheus][unknown] Prometheus Exporter is dropping a message to http://0.0.0.0:9395/send-metrics: Failed to open TCP connection to 0.0.0.0:9395 (Connection refused - connect(2) for "0.0.0.0" port 9395)

After fix (Protorabbit.new.start called, then a metric pushed via Bigcommerce::Prometheus.client):

$ curl -s localhost:9394/metrics | grep protorabbit_smoke_test
# HELP ruby_protorabbit_smoke_test_total smoke test
# TYPE ruby_protorabbit_smoke_test_total counter
ruby_protorabbit_smoke_test_total 1

Exporter starts, registers collectors, and serves the pushed metric on /metrics — no connection refused.

Manual checklist for reviewer:

• Confirm README's Protorabbit section matches the intended integration pattern for a consuming service
• Confirm 0.9.0 version bump and CHANGELOG entry are accurate

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Note

Low Risk
Opt-in at call sites via .start; mirrors existing Hutch/Resque server startup with no change to Web/Resque/Hutch until services wire it in.

Overview
Adds Bigcommerce::Prometheus::Instrumentors::Protorabbit so protorabbit (RabbitMQ protobuf consumer) workers can start the same embedded Prometheus exporter used by Web/Resque/Hutch. Without it, metrics pushed during message handling hit Errno::ECONNREFUSED on /send-metrics because nothing listens on the exporter port.

Call Protorabbit.new.start in protorabbit boot code (no app: argument—unlike Hutch). The instrumentor registers ActiveRecordCollector, the ActiveRecord SQL type collector, configured protorabbit_collectors / protorabbit_type_collectors, then starts the server and polling collectors. It does not wrap message processing (no Hutch-style middleware); it only enables ingestion of metrics already emitted from handlers (e.g. gRPC client interceptors).

Configuration adds protorabbit_collectors and protorabbit_type_collectors (default []). Gem version bumps to 0.9.0 with CHANGELOG/README updates and a new protorabbit_spec covering disabled noop, enabled startup order, and error rescue.

^{Reviewed by Cursor Bugbot for commit 61ca592. Bugbot is set up for automated code reviews on this repo. Configure here.}

[Copilot]

Pull request overview

Adds opt-in Protorabbit worker instrumentation so Prometheus metrics can reach an embedded exporter.

Changes:

• Adds and tests the Protorabbit instrumentor.
• Adds collector configuration and integration documentation.
• Releases the feature as version 0.9.0.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lib/bigcommerce/prometheus/instrumentors/protorabbit.rb	Implements exporter startup and collector registration.
spec/bigcommerce/prometheus/instrumentors/protorabbit_spec.rb	Tests startup, configuration, disabled behavior, and failures.
lib/bigcommerce/prometheus/configuration.rb	Adds Protorabbit collector settings.
lib/bigcommerce/prometheus.rb	Loads the new instrumentor.
README.md	Documents setup and configuration.
CHANGELOG.md	Records the new feature.
lib/bigcommerce/prometheus/version.rb	Bumps the gem to 0.9.0.

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