PMM-15228 Enrich AuthServer with performance metrics

[maxkondr]

Ticket number: PMM-15228

Percona-Lab/pmm-submodules#4481

This pull request introduces comprehensive Prometheus metrics to the AuthServer in the Grafana authentication service, enabling detailed monitoring of authentication requests, cache performance, and latency. The changes include metric definitions, collection, and registration, as well as instrumentation of key code paths to increment relevant counters and histograms.

Prometheus Metrics Integration:

• Added Prometheus metric fields and descriptors to the AuthServer struct, including counters for authentication requests, cache hits/misses, in-flight requests, and latency histograms. Implemented the prom.Collector interface with Describe and Collect methods. [1] [2]

• Instrumented the main authentication flow (ServeHTTP, getLBACFilters, getAuthUser, retrieveRole) to increment metrics for request counts, cache hits/misses, in-flight requests, and operation durations. [1] [2] [3] [4] [5] [6] [7]

Application Integration:

• Registered the AuthServer as a Prometheus collector in the main application entrypoint to ensure metrics are exposed.

Dependency and Import Updates:

• Added imports for Prometheus client, atomic operations, and other standard library packages needed for metrics and concurrency.

Other Minor Improvements:

• Improved code comments and logging level checks for better maintainability and debugging.

These enhancements provide greater observability into authentication performance and reliability, supporting future troubleshooting and scaling efforts.

[codecov]

Codecov Report

❌ Patch coverage is 54.71698% with 48 lines in your changes missing coverage. Please review.
✅ Project coverage is 42.44%. Comparing base (31318c7) to head (54d3d8a).
⚠️ Report is 39 commits behind head on main.

Files with missing lines	Patch %	Lines
managed/services/grafana/auth_server.go	55.23%	47 Missing ⚠️
managed/cmd/pmm-managed/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5658      +/-   ##
==========================================
- Coverage   43.59%   42.44%   -1.15%     
==========================================
  Files         415      431      +16     
  Lines       43134    34925    -8209     
  Branches        0      591     +591     
==========================================
- Hits        18804    14824    -3980     
+ Misses      22454    18675    -3779     
+ Partials     1876     1426     -450     

Flag	Coverage Δ
admin	34.96% <ø> (+0.17%)	⬆️
agent	?
managed	43.83% <54.71%> (+0.85%)	⬆️
unittests	41.29% <ø> (?)
vmproxy	?

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[Copilot]

Pull request overview

This PR adds Prometheus observability to the Grafana AuthServer in pmm-managed, exposing request/cache/latency metrics and wiring the server into the Prometheus registry, plus updating the PMM Health Grafana dashboard to visualize the new signals.

Changes:

• Implemented a custom Prometheus collector in AuthServer with counters/gauges/histograms for auth requests, Grafana calls, cache behavior, in-flight requests, and latencies.
• Registered the AuthServer collector during pmm-managed startup so metrics are exposed automatically.
• Updated the PMM Health dashboard to include panels for the new auth metrics and additional runtime/health visualizations.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 9 comments.

File	Description
managed/services/grafana/auth_server.go	Adds Prometheus metric descriptors/state, implements prometheus.Collector, and instruments key auth/cache/DB/Grafana code paths.
managed/cmd/pmm-managed/main.go	Registers the AuthServer as a Prometheus collector at startup.
dashboards/dashboards/PMM Health/PMM_Health.json	Adds/adjusts dashboard panels and queries to surface new auth metrics and runtime health info.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 3 changed files in this pull request and generated 3 comments.