haproxy-session-average.rb

#!/usr/bin/env ruby

require 'csv'
require 'socket'

class AverageSessionsPerServer
  Server = Struct.new(:name, :current_sessions, :status) do
    META_SERVER_NAMES = ['FRONTEND', 'BACKEND'].freeze

    def up?
      status == 'UP'
    end

    def sessions
      current_sessions.to_i
    end

    def meta?
      META_SERVER_NAMES.include? name
    end
  end

  def initialize(stats)
    @stats = stats
  end

  def aggregate
    result = total_sessions.to_f / number_of_servers_up.to_f
    result.finite? ? result : 0.0
  end

  def print_to(stream)
    stream.puts aggregate
  end

  def number_of_servers_up
    servers.select(&:up?).size
  end

  def total_sessions
    servers.map(&:sessions).inject(0) { |mem, obj| mem + obj }
  end

  def servers
    rows = CSV.parse(@stats, headers: true)
    rows.map do |row|
      Server.new(row['svname'], row['scur'], row['status'])
    end.reject(&:meta?)
  end
end

class HAProxySocket
  SHOW_STATS_COMMAND = 'show stat'.freeze

  def initialize(socket_path)
    @socket_path = socket_path
  end

  def show_stats
    response_to SHOW_STATS_COMMAND
  end

  def response_to(command)
    socket = UNIXSocket.new(@socket_path)
    socket.puts command
    socket.read
  end
end

stat = AverageSessionsPerServer.new(HAProxySocket.new("/tmp/.haproxy.sock").show_stats)
stat.print_to STDOUT