Puma Plugin for getting puma stats

README.md

Puma Stats Logger - plugin for collecting puma metrics

to configure this plugin, add following in your puma.rb

# plugin to send server stats to our monitoring systems
# export SERVER_STATS_FREQUENCY (seconds) to control the frequency
plugin :stats_logger

NOTE: we keep plugin in lib/puma/plugin/stats_logger.rb, IIRC it is required because of the way puma loads plugins

Update: also checkout https://github.com/harmjanblok/puma-metrics if you are looking for prom metrics

stats_logger.rb

# frozen_string_literal: true

# Puma plugin for sending puma and db connection stats to our monitoring systems
# Taken from: https://gist.github.com/LeZuse/022c501143a5bc4b51a601ad2a1b8abc
# See: https://github.com/puma/puma/issues/1512 to know more about these metrics
# Docs: https://github.com/puma/puma/blob/master/docs/plugins.md

require 'puma/plugin'

Puma::Plugin.create do
  # return true if you want to send stats
  # return false if you want to disable this plugin
  def send_stats?
    # do not send stats on development test and beta
    env = Rails.env
    return false if %w[development test beta].include?(env)

    # send stats
    return true
  end

  def start(_launcher)
    return unless send_stats?

    in_background do
      stat_frequency = ENV.fetch('SERVER_STATS_FREQUENCY', 10).to_i
      Rails.logger.warn("Sending server stats every #{stat_frequency} seconds")

      loop do
        sleep(stat_frequency)
        begin
          all_stats = {}
          puma_stats = []
          db_pool_stats = []

          # Puma.stats: {
          #        started_at: @started_at.utc.iso8601,
          #        workers: @workers.size,
          #        phase: @phase,
          #        booted_workers: worker_status.count { |w| w[:booted] },
          #        old_workers: old_worker_count,
          #        worker_status: worker_status,
          #      }
          stats = JSON.parse(Puma.stats, symbolize_names: true)
          # get puma stats
          if stats[:worker_status].present?
            # in cluster mode, get stats from each worker
            # stats[:worker_status]: List of workers with their corresponding
            #                        statuses
            stats[:worker_status].each do |worker|
              # worker[:last_status]: { "backlog":0,"running":2,
              #                         "pool_capacity":2,"max_threads":2 }
              stat = worker[:last_status]
              puma_stats << stat
            end
          else
            puma_stats << stats
          end
          # get db pool stats
          db_stat = ActiveRecord::Base.connection_pool.stat
          # checkout_timeout is sometimes float, make int to make sure events
          # are not dropped by InfluxDB
          db_stat[:checkout_timeout] = db_stat[:checkout_timeout].to_i
          db_pool_stats << db_stat

          # build final stats hash
          all_stats['puma'] = puma_stats
          all_stats['db_pool'] = db_pool_stats
          # this call sends it to monitoring system
          ServerMetrics.push_stats(all_stats)
        rescue StandardError => e
          Rails.logger.warn(e)
        ensure
          # flush logger
          Rails.logger.flush
        end
      end
    end
  end
end