feat: Add `prometheus.echo` component for local metrics inspection by iamrajiv · Pull Request #4105 · grafana/alloy

iamrajiv · 2025-08-02T07:04:27Z

PR Description

The component provides local inspection of Prometheus metrics by outputting them to stdout in a human-readable format, making debugging and testing much easier.

Which issue(s) this PR fixes

Fixes: #3738

Notes to the Reviewer

PR Checklist

CHANGELOG.md updated
Documentation added
Tests updated
Config converters updated

CLAassistant · 2025-08-02T07:04:35Z

All committers have signed the CLA.

iamrajiv · 2025-08-02T07:05:43Z

can you review @dehaansa @smaddock?

dehaansa · 2025-08-04T16:14:12Z

Can this be refactored to use the upstream encoding(s)? For example the expfmt encoder from the prometheus/common package expfmt.NewEncoder(&output, expfmt.NewFormat(expfmt.TypeTextPlain)), and then when things are appended store them using MetricFamily proto rather than an struct unique to this component. This will reduce maintenance requirements on the component and ensure we stay consistent with the upstream, and also allow users to pick a different exposition format if we allow.

iamrajiv · 2025-08-04T16:29:29Z

sure @dehaansa will use prometheus expfmt encoder instead of custom string formatting and standard dto.MetricFamily protocol buffer

dehaansa · 2025-10-06T21:03:06Z

Sorry that this dropped off our radar - it looks good, but needs a docs page.

iamrajiv · 2025-10-07T19:25:12Z

added the doc @dehaansa can you review ?

docs/sources/reference/components/prometheus/prometheus.echo.md

iamrajiv · 2025-10-08T21:36:06Z

Thanks for reviewing and for the commit, @clayton-cornell. Could you review @dehaansa’s one more time?

dehaansa

Sorry that this slipped off my radar - LGTM. Once CI is happy, we can merge.

clayton-cornell · 2025-11-21T20:47:01Z

@iamrajiv When you have a moment, can you please sign the CLA. It's a requirement for moving forward on your PR. :-)

Copilot

Pull request overview

This PR adds a new prometheus.echo component that receives Prometheus metrics and writes them to stdout in a human-readable format for debugging and testing purposes. The component mirrors the existing loki.echo component functionality but for Prometheus metrics instead of logs.

Key changes:

New prometheus.echo component with configurable output format (text or OpenMetrics)
Complete test coverage including format validation and metrics processing
Documentation following the existing component doc structure

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
internal/component/prometheus/echo/echo.go	Core component implementation with storage.Appendable interface, format encoding, and metric family building
internal/component/prometheus/echo/echo_test.go	Comprehensive test suite covering component lifecycle, appender operations, and format outputs
internal/component/all/all.go	Component registration in the global import list
docs/sources/reference/components/prometheus/prometheus.echo.md	Complete component documentation with usage examples and compatibility info
CHANGELOG.md	Release notes entry documenting the new feature

Copilot · 2025-11-21T21:02:14Z

internal/component/prometheus/echo/echo.go

+	for k := range a.samples {
+		delete(a.samples, k)
+	}
+	for k := range a.exemplars {
+		delete(a.exemplars, k)
+	}
+	for k := range a.histograms {
+		delete(a.histograms, k)
+	}
+	for k := range a.metadata {
+		delete(a.metadata, k)
+	}


Instead of iterating and deleting keys individually, consider reinitializing the maps with make() which is more efficient: a.samples = make(map[string]sample) etc.

Suggested change

for k := range a.samples {

delete(a.samples, k)

}

for k := range a.exemplars {

delete(a.exemplars, k)

}

for k := range a.histograms {

delete(a.histograms, k)

}

for k := range a.metadata {

delete(a.metadata, k)

}

a.samples = make(map[string]sample)

a.exemplars = make(map[string]seriesExemplar)

a.histograms = make(map[string]seriesHistogram)

a.metadata = make(map[string]metadata.Metadata)

Copilot · 2025-11-21T21:02:15Z

internal/component/prometheus/echo/echo_test.go

+		require.NoError(t, err)
+	}()
+
+	time.Sleep(100 * time.Millisecond)


Using time.Sleep in tests creates flakiness and unnecessarily slows down test execution. Consider using synchronization primitives or channels to properly wait for the component to start, or remove this line if it's not essential for the test.

docs/sources/reference/components/prometheus/prometheus.echo.md

dehaansa · 2025-12-10T02:43:14Z

@iamrajiv this should be ready, but it seems the CLA check has lost your info, can you resign the CLA?

iamrajiv · 2025-12-10T09:27:01Z

@dehaansa done can you check now

dehaansa · 2025-12-10T14:31:09Z

@dehaansa done can you check now

The CLA Assistant seems to still think you haven't accepted: #4105 (comment)

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

…rafana#4862) * Introduce new dependency management tool * Move syntax replace to top of go.mod to avoid confusion * Apply replaces from tool * Introduce PR workflow to check modules are synced * Add E2E test * Address some PR comments Co-authored-by: Piotr <17101802+thampiotr@users.noreply.github.com> * Refactor to use a centralised cobra CLI, called by generate.go * Refactor to not generate .txt files and pass replace text in memory * Refactor E2E tests to use explicit test data * Update tools/generate-module-dependencies/replaces-mod.tpl Co-authored-by: Kyle Eckhart <kgeckhart@users.noreply.github.com> * Return errors in FileHelper instead of using Fatalf * Address PR comments * go mod/mod changes * Reference actual calculated file to dependency yaml file in error logs * Group the generate-module-dependencies and Check for go.mod changes properly in workflow and use git diff instead so we can ignore whitespace changes * nit: a few improvements for clarity --------- Co-authored-by: Piotr <17101802+thampiotr@users.noreply.github.com> Co-authored-by: Kyle Eckhart <kgeckhart@users.noreply.github.com>

…ana#5010) * fix: add StoreBuilder to mimir.alerts.kubernetes eventProcessor Fixes grafana#4975 * Add integration and unit tests * Fix lint error * Add changelog entry --------- Co-authored-by: Paulin Todev <paulin.todev@gmail.com>

* Add some high level pipeline tests for prometheus * Remove labelstore interactions from the interceptor * Move back to uber atomic and fix flaky remote write test * One more thing to move back to uber atomic * Actually fix the flaky test and lints * Fix flaky test for real and add a comment to Fanout about its role in global labels * Put componentID back on fanout for now

* Improve docker's multiplexed long lines handling * Fix `dockerChunkWriter` buffer flushing and add test for it * Update `CHANGELOG.md` * Fix potential panic in `extractTsFromBytes` and `dockerChunkWriter` buffer allocation

iamrajiv requested a review from a team as a code owner August 2, 2025 07:04

iamrajiv requested a review from clayton-cornell as a code owner October 7, 2025 19:24

clayton-cornell reviewed Oct 7, 2025

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dehaansa approved these changes Oct 27, 2025

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clayton-cornell added the type/docs Docs Squad label across all Grafana Labs repos label Nov 21, 2025

clayton-cornell requested a review from Copilot November 21, 2025 20:52

Copilot started reviewing on behalf of clayton-cornell November 21, 2025 20:52 View session

Copilot finished reviewing on behalf of clayton-cornell November 21, 2025 20:54

Copilot AI reviewed Nov 21, 2025

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clayton-cornell approved these changes Nov 26, 2025

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docs/sources/reference/components/prometheus/prometheus.echo.md Outdated Show resolved Hide resolved

dehaansa enabled auto-merge (squash) December 9, 2025 04:54

iamrajiv requested a review from dehaansa December 10, 2025 15:25

iamrajiv and others added 7 commits December 10, 2025 10:56

add echo

6d9a4fc

add test

f2347b7

add changelog

a253d8e

use prometheus expfmt encoder

1e44b4e

add doc

df366c9

Update docs/sources/reference/components/prometheus/prometheus.echo.md

ad2d3a7

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

Update docs/sources/reference/components/prometheus/prometheus.echo.md

1622764

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

iamrajiv and others added 17 commits December 10, 2025 10:57

Update docs/sources/reference/components/prometheus/prometheus.echo.md

9d0b21e

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

Update docs/sources/reference/components/prometheus/prometheus.echo.md

9a983e7

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

Update docs/sources/reference/components/prometheus/prometheus.echo.md

db423cb

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

Update docs/sources/reference/components/prometheus/prometheus.echo.md

5e42d55

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

Update docs/sources/reference/components/prometheus/prometheus.echo.md

a3d0388

Co-authored-by: Clayton Cornell <131809008+clayton-cornell@users.noreply.github.com>

Fix build issues

f1b5fed

Appease linter and regenerate things

53d52d3

update to go v1.25.5 (grafana#5027)

42a04f4

Add changelog for PR 5002 (grafana#5042)

e1f5704

Fix missing release note for v1.12 (grafana#5043)

390d445

update changelog

c38d836

add cloud-provider labels to target metrics (grafana#4942)

c48fc0d

stop storage and wal after test (grafana#5056)

3941a47

dehaansa force-pushed the ins branch from aaf2d8c to 3941a47 Compare December 10, 2025 15:57

dehaansa requested a review from a team as a code owner December 10, 2025 15:57

Merge branch 'main' into ins

21d3b2b

dehaansa merged commit 7f6d0d2 into grafana:main Dec 10, 2025
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