Class: Lens::Rails::MetricsExporter

Inherits:
Object
  • Object
show all
Defined in:
lib/lens/rails/metrics_exporter.rb

Overview

Rack middleware that tracks request counts and durations, flushing them to Lens every 30 s via POST /v1/metrics.

Constant Summary collapse

RESERVOIR_SIZE = 
1024

Instance Method Summary collapse

Constructor Details

#initialize(app, url:, token:, service_name:, open_timeout: 2, read_timeout: 2) ⇒ MetricsExporter

Returns a new instance of MetricsExporter.



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# File 'lib/lens/rails/metrics_exporter.rb', line 13

def initialize(app, url:, token:, service_name:,
  open_timeout: 2,
  read_timeout: 2)
  @app = app
  @token = token
  @service_name = service_name
  @uri = URI("#{url}/v1/metrics")
  @open_timeout = open_timeout
  @read_timeout = read_timeout
  @mutex = Mutex.new
  reset_window
  restart_flush_thread
  Lens::Rails.register_flushable(self)
end

Instance Method Details

#call(env) ⇒ Object 



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# File 'lib/lens/rails/metrics_exporter.rb', line 28

def call(env)
  Thread.current[:lens_request_id] = env["action_dispatch.request_id"]
  wall_start = Time.now
  start = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  status, headers, body = @app.call(env)
  duration = (Process.clock_gettime(Process::CLOCK_MONOTONIC) - start) * 1000.0
  queue_time = parse_queue_time(env, wall_start)

  @mutex.synchronize do
    @request_count += 1
    @error_count += 1 if status >= 500
    @duration_sum += duration
    @duration_min = duration if @duration_min.nil? || duration < @duration_min
    @duration_max = duration if @duration_max.nil? || duration > @duration_max
    if @samples.size < RESERVOIR_SIZE
      @samples << duration
    else
      idx = rand(@request_count)
      @samples[idx] = duration if idx < RESERVOIR_SIZE
    end
    if queue_time
      @queue_samples << queue_time
      @queue_sum += queue_time
    end
  end

  [status, headers, body]
ensure
  Thread.current[:lens_request_id] = nil
end

#flush ⇒ Object 



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# File 'lib/lens/rails/metrics_exporter.rb', line 59

def flush
  snapshot = @mutex.synchronize do
    s = {count: @request_count, errors: @error_count,
         sum: @duration_sum, min: @duration_min, max: @duration_max,
         samples: @samples, queue_samples: @queue_samples, queue_sum: @queue_sum}
    reset_window
    s
  end

  return if snapshot[:count].zero?

  now = Time.now.iso8601(3)
  avg = snapshot[:sum] / snapshot[:count]
  p50 = percentile(snapshot[:samples], 0.50)
  p95 = percentile(snapshot[:samples], 0.95)

  metrics = [
    {name: "http.server.request_count", unit: "1", value: snapshot[:count].to_f, timestamp: now},
    {name: "http.server.error_count", unit: "1", value: snapshot[:errors].to_f, timestamp: now},
    {name: "http.server.duration", unit: "ms", value: avg, timestamp: now},
    {name: "http.server.duration.p50", unit: "ms", value: p50, timestamp: now},
    {name: "http.server.duration.p95", unit: "ms", value: p95, timestamp: now}
  ]

  if snapshot[:queue_samples].any?
    q_avg = snapshot[:queue_sum] / snapshot[:queue_samples].size
    q_p50 = percentile(snapshot[:queue_samples], 0.50)
    q_p95 = percentile(snapshot[:queue_samples], 0.95)
    metrics += [
      {name: "http.server.queue_time", unit: "ms", value: q_avg, timestamp: now},
      {name: "http.server.queue_time.p50", unit: "ms", value: q_p50, timestamp: now},
      {name: "http.server.queue_time.p95", unit: "ms", value: q_p95, timestamp: now}
    ]
  end

  body = JSON.generate(metrics: metrics, service: @service_name, version: Lens::Rails::VERSION)

  req = Net::HTTP::Post.new(@uri)
  req["Content-Type"] = "application/octet-stream"
  req["Authorization"] = "Bearer #{@token}"
  req.body = Zlib.gzip(body)

  Thread.current[:lens_in_export] = true
  begin
    Net::HTTP.start(@uri.host, @uri.port,
      use_ssl: @uri.scheme == "https",
      open_timeout: @open_timeout,
      read_timeout: @read_timeout) { |http| http.request(req) }
  ensure
    Thread.current[:lens_in_export] = false
  end
end

#restart_flush_thread ⇒ Object 



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# File 'lib/lens/rails/metrics_exporter.rb', line 117

def restart_flush_thread
  BackoffLoop.new(base: 30, max: 120, name: "lens-metrics-flush").start { flush }
end

#shutdown(timeout:) ⇒ Object 



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# File 'lib/lens/rails/metrics_exporter.rb', line 112

def shutdown(timeout:)
  Thread.new { flush }.join(timeout)
rescue
end