Middleware that logs heroku requests into redis.

heroku_env_logger.rb

require "csv"

class HerokuEnvLogger
  PREFIX    = "HerokuRequest"
  TIME_STEP = 1.minute * 1000 # ms
  EXPIRE_IN = 6.hours
  KEYS      = %w[HTTP_X_REQUEST_START
                 HTTP_X_HEROKU_QUEUE_WAIT_TIME
                 HTTP_X_HEROKU_QUEUE_DEPTH
                 HTTP_X_HEROKU_DYNOS_IN_USE]


  # IN MS - from http request
  class << self
    def key(ms)
      timestamp = ms.to_i
      "#{PREFIX}:#{timestamp - (timestamp % TIME_STEP)}"
    end

    # IN SECS - for rails
    def get(seconds)
      get_by_ms seconds.to_i * 1000
    end

    def between(a, b)
      first, last = [a,b].map{|n| n.to_i * 1000 }.sort
      get_by_ms *(first..last).step(TIME_STEP)
    end

    def get_by_ms(*ms)
      keys   = ms.map{|k| key(k) }
      values = $redis.mget(keys)

      CSV.parse values.compact.join("")
    end
  end

  def initialize(app)
    @app = app
  end

  def call(env)
    log_request env
    @app.call env
  end

  def log_request(env)
    data = KEYS.map {|k| env[k] }
    key  = self.class.key data.first
    csv  = CSV.generate_line data

    $redis.append key, csv
    $redis.expire key, EXPIRE_IN
  rescue StandardError => e
    Rails.logger.error(e)
  end
end