health_server.rb

require 'webrick'
require 'json'
require_relative 'health_reporter'

module Geronimo
  # Geronimo::HealthServer is a HTTP server which is intended to run alongside
  # services which do not have an HTTP server.
  #
  # For example, a service like Sidekiq might extend the class to offer
  # health checks related to Sidekiq functions
  #
  #   class SidekiqHealthServer < Geronimo::HealthServer
  #     define_check('redis') do |reporter|
  #       reporter.report_redis
  #     end
  #   end
  class HealthServer
    def initialize(options)
      @port = ENV['HEALTHCHECK_SERVER_PORT'].to_i
      @health_reporter = Geronimo::HealthReporter.new
      @logger = options[:logger]

      @server = WEBrick::HTTPServer.new(:Port => @port, :Logger => @logger)
      @server.mount_proc '/' do |req, res|
        j = handle_web(req, res)
        res.status = 200
        res['Content-Type'] = 'application/json'
        res.body = JSON.generate(j)
      end
    end

    def self.checks
      @@checks ||= []
    end

    def self.define_check(name, &block)
      checks.push(block)
    end

    # return some some data structure which will be marshaled as JSON
    def handle_web(req, res)
      @@checks.map do |checker|
        checker.call(@health_reporter)
      end
    end

    # starts an http server in a thread
    def start_server_thread
      Thread.start do
        @logger.info "Starting health check server on #{@port}"
        begin
          @server.start
        rescue Interrupt
          @logger.info "Health check server shut down"
        end
      end
    end
  end
end

require 'logger'

class SidekiqHealthServer < Geronimo::HealthServer
  define_check('redis') do |reporter|
    reporter.report_redis 'sidekiq'
  end
end

l = Logger.new(STDOUT)
sq = SidekiqHealthServer.new(logger: l)
sq.start_server_thread.join