Document Prometheus metrics and OLAP Flow events

[tanveergill]

What

• Add a docs section at References/Metrics: A catalog (a table per sub-section) of all metrics in Aperture.
  • Format of metrics table
    • Metric Name: Name of the metric
    • Metric Type: Type of Prometheus metric (Histogram, Summary, Counter etc.)
    • Labels: Default labels available on the metric
    • Unit: ms, %age, byte, count (no unit) etc. See units reference in Prometheus docs
    • Description: Description of the metric
  • Format of labels table (for documenting labels across all sub-sections)
    • Label Name: Name of the label
    • Example Values: List all or few possible examples
    • Description: Description of the metric
  • Sub-sections
    • Aperture System Common
      • Job metrics
      • Go process metrics
      • etc.
    • Agent metrics
      • FluxMeter
      • ConcurrencyLimiter
      • RateLimiter
      • Classifier
      • Dataplane Summary (flowcontrol_requests_total, distcache_entries_total etc.)
    • Controller metrics
      • Signal metrics
  • Source of truth
    • Metric schema file
    • Can jump to references of metric name to find the Prometheus register call which should have the description. See example.
• Add a docs section at References/Flow Events: Schema (table) of Flow events
  • Format of Dimension Columns table
    • Dimension Name: Name of the dimension
    • Dimension Type: Whether it's a single or multi-value dimension
    • Example Values: List all or few possible examples
    • Description: Description of the dimension
    • Flow Control Integrations: The Flow Control Integrations in which this dimension is available. Example Armeria HTTP, Armeria RPC, Envoy
  • Format of Metric Columns table
    • Metric Name: Name of the metric
    • Metric Type: Integer, Float or Quantile DataSketch
    • Rollup Type: Max, Min, Sum, Quantile DataSketch
    • Unit: ms, %age, byte, count (no unit) etc.
    • Description: Description of the metric
  • Source of truth
    • Dimension include lists
    • Dimension value examples
    • Metric aggregates