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Merged
merged 5 commits into from
Jun 28, 2025
Merged

Add prometheus metrics to subsonic and plugins #4266

merged 5 commits into from
Jun 28, 2025

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kgarner7
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This exposes the following metrics:

  • Subsonic
    • Method counts by endpoint, HTTP method, and HTTP code
    • Latency (50%, 90%, 99% quartiles), as well as total elapsed
  • Plugin
    • Calls by plugin name, method, and whether the response is ok. Note that this should ignore nil/not implemented responses.
    • Same latency calculations as latency

Note that prometheus is now a singleton, so that it can be passed around much easier to plugins.
Consequently, the scan metrics require passing in the database now.

I'd like to also support native API, but that's trickier as there are URL fragments.

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Summary of Changes

Hello @kgarner7, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the observability of the application by integrating comprehensive Prometheus metrics for both the Subsonic API and plugin interactions. The core change involves refactoring the Prometheus instance into a singleton, which streamlines its usage throughout the codebase and enables detailed performance and usage monitoring.

Highlights

  • New Prometheus Metrics for Subsonic API: I've introduced new Prometheus metrics to track Subsonic API requests. These include method counts by endpoint, HTTP method, and HTTP status code, as well as latency measurements (50th, 90th, and 99th percentiles, plus total elapsed time) for these requests.
  • New Prometheus Metrics for Plugins: Similarly, I've added Prometheus metrics for plugin calls. These metrics capture call counts by plugin name, method, and whether the response was successful. Latency calculations (50th, 90th, and 99th percentiles, and total elapsed time) are also included for plugin interactions.
  • Prometheus Instance Refactor to Singleton: The Prometheus metrics instance has been refactored to be a singleton. This change simplifies its management and passing across different parts of the application, making it more accessible for various components to record metrics.
  • DataStore Dependency for Scan Metrics: As a consequence of the Prometheus singleton refactor, the DataStore is now explicitly passed as an argument to functions that write scan-related metrics (e.g., WriteInitialMetrics, WriteAfterScanMetrics), rather than being held directly by the metrics instance.
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Code Review

This pull request introduces Prometheus metrics for Subsonic API endpoints and for plugin calls, which is a great addition for observability. The implementation is mostly solid, using a singleton for the Prometheus instance and a middleware for capturing HTTP metrics.

I've identified a couple of areas for improvement:

  • A bug in the plugin metric recording logic due to a shadowed variable.
  • An opportunity to refactor repetitive code in metric registration for better maintainability.
  • A minor naming issue for clarity.

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github-actions bot commented Jun 26, 2025 •
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@kgarner7
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Sample data collected (example using my listenbrainz plugin):

# HELP http_request_count Request types by status
# TYPE http_request_count counter
http_request_count{endpoint="/rest/getArtistInfo",method="GET",status="200"} 3
# HELP http_request_latency Latency (in ms) of HTTP requests
# TYPE http_request_latency summary
http_request_latency{endpoint="/rest/getArtistInfo",method="GET",quantile="0.5"} 32
http_request_latency{endpoint="/rest/getArtistInfo",method="GET",quantile="0.75"} 32
http_request_latency{endpoint="/rest/getArtistInfo",method="GET",quantile="0.9"} 32
http_request_latency{endpoint="/rest/getArtistInfo",method="GET",quantile="0.99"} 32
http_request_latency_sum{endpoint="/rest/getArtistInfo",method="GET"} 89
http_request_latency_count{endpoint="/rest/getArtistInfo",method="GET"} 3
# HELP plugin_request_count Plugin requests by method/status
# TYPE plugin_request_count counter
plugin_request_count{method="GetArtistURL",ok="true",plugin="brainz"} 3
plugin_request_count{method="GetSimilarArtists",ok="true",plugin="brainz"} 3
# HELP plugin_request_latency Latency (in ms) of plugin requests
# TYPE plugin_request_latency summary
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.5"} 356
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.75"} 1052
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.9"} 1052
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.99"} 1052
plugin_request_latency_sum{method="GetArtistURL",plugin="brainz"} 1754
plugin_request_latency_count{method="GetArtistURL",plugin="brainz"} 3
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.5"} 219
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.75"} 734
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.9"} 734
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.99"} 734
plugin_request_latency_sum{method="GetSimilarArtists",plugin="brainz"} 1167
plugin_request_latency_count{method="GetSimilarArtists",plugin="brainz"} 3

@kgarner7 kgarner7 marked this pull request as ready for review June 28, 2025 00:18
@kgarner7
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Updated example, with openmetrics:

# HELP http_request_count Request types by status
# TYPE http_request_count unknown
http_request_count{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET",status="200"} 1.0
http_request_count_created{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET",status="200"} 1.751071149915913e+09
# HELP http_request_latency Latency (in ms) of HTTP requests
# TYPE http_request_latency summary
http_request_latency{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET",quantile="0.5"} 40.0
http_request_latency{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET",quantile="0.75"} 40.0
http_request_latency{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET",quantile="0.9"} 40.0
http_request_latency{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET",quantile="0.99"} 40.0
http_request_latency_sum{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET"} 40.0
http_request_latency_count{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET"} 1
http_request_latency_created{client="Insomnium",endpoint="/rest/getArtistInfo",method="GET"} 1.7510711499159539e+09
# HELP navidrome_info Information about Navidrome version
# TYPE navidrome_info gauge
navidrome_info{version="dev"} 1.0
# HELP plugin_request_count Plugin requests by method/status
# TYPE plugin_request_count unknown
plugin_request_count{method="GetArtistURL",ok="true",plugin="brainz"} 1.0
plugin_request_count_created{method="GetArtistURL",ok="true",plugin="brainz"} 1.7510711513092005e+09
plugin_request_count{method="GetSimilarArtists",ok="true",plugin="brainz"} 1.0
plugin_request_count_created{method="GetSimilarArtists",ok="true",plugin="brainz"} 1.751071151120421e+09
# HELP plugin_request_latency Latency (in ms) of plugin requests
# TYPE plugin_request_latency summary
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.5"} 1109.0
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.75"} 1109.0
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.9"} 1109.0
plugin_request_latency{method="GetArtistURL",plugin="brainz",quantile="0.99"} 1109.0
plugin_request_latency_sum{method="GetArtistURL",plugin="brainz"} 1109.0
plugin_request_latency_count{method="GetArtistURL",plugin="brainz"} 1
plugin_request_latency_created{method="GetArtistURL",plugin="brainz"} 1.7510711513092449e+09
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.5"} 768.0
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.75"} 768.0
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.9"} 768.0
plugin_request_latency{method="GetSimilarArtists",plugin="brainz",quantile="0.99"} 768.0
plugin_request_latency_sum{method="GetSimilarArtists",plugin="brainz"} 768.0
plugin_request_latency_count{method="GetSimilarArtists",plugin="brainz"} 1
plugin_request_latency_created{method="GetSimilarArtists",plugin="brainz"} 1.7510711511204865e+09

(The tiemstamp indicates metric creation time)

@deluan deluan merged commit 0cd15c1 into navidrome:master Jun 28, 2025
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@BrewTestBot BrewTestBot mentioned this pull request Jul 1, 2025
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