How to post alerts from Monit to Slack

post_to_slack.rb

# encoding: UTF-8

require 'optparse'
require 'net/http'
require 'json'

def parse_options(argv)
  opts = {}

  @parser = OptionParser.new do |o|
    o.on '--channel CHANNEL', "name of the channel to post to" do |arg|
      opts[:channel] = arg
    end

    o.on '--name NAME', "name of the bot" do |arg|
      opts[:name] = arg
    end

    o.on '--emoji EMOJI', "emoji icon" do |arg|
      opts[:emoji] = arg
    end

    o.on '--token TOKEN', "authentication token" do |arg|
      opts[:token] = arg
    end

    o.on '--status [error,ok]', "kind of message" do |arg|
      opts[:status] = arg
    end

    o.on '--color #HEX_COLOR', "color of the message" do |arg|
      opts[:color] = arg
    end

    o.on '--slack-url URL', "URL to post to" do |arg|
      opts[:slack_url] = arg
    end

    o.on '--monit-url URL', "URL of Monit" do |arg|
      opts[:monit_url] = arg
    end

    o.on '--text TEXT', "text of the message" do |arg|
      opts[:text] = arg
    end

    o.on '--service SERVICE', "Monit service affected" do |arg|
      opts[:service] = arg
    end
  end

  @parser.banner = "post_to_slack [options]"
  # @parser.on_tail "-h", "--help", "Show help" do
  #   logger.info @parser
  #   die 1
  # end
  @parser.parse!(argv)
  
  opts[:channel]   ||= ENV.fetch('CHANNEL') { '#general' }
  opts[:name]      ||= ENV.fetch('NAME') { 'Monit' }
  opts[:emoji]     ||= ENV.fetch('EMOJI') { ':vertical_traffic_light:' }
  opts[:token]     ||= ENV.fetch('TOKEN') { '_your_token_' }
  opts[:status]    ||= ENV.fetch('STATUS') { 'unknown' }
  opts[:slack_url] ||= ENV.fetch('SLACK_URL') { "https://_you_.slack.com/services/hooks/incoming-webhook" }
  opts[:monit_url] ||= ENV.fetch('MONIT_URL') { "http://#{`hostname -f`.chomp}:2812/" }
  
  opts[:color] ||= case opts[:status]
  when 'ok'
    '#59A452'
  when 'error'
    '#d00000'
  else
    '#cccccc'
  end

  opts
end

def format_payload(opts = {})
{
  "channel" => opts[:channel],
  "icon_emoji" => opts[:emoji],
  "username" => opts[:name],
  "text" => "Issue on #{`hostname`.chomp} : #{opts[:text]}",
  "attachments" => [{
    "fallback" => "#{opts[:text]}\n#{opts[:monit_url]}#{opts.fetch(:service){'#'}}",
    "color" => opts[:color],
    "fields" => [{
      "title" => "Message",
      "value" => opts[:text],
      "short" => true
    },{
      "title" => "URL",
      "value" => "<#{opts[:monit_url]}#{opts.fetch(:service){'#'}}|#{opts.fetch(:service){'?'}}>",
      "short" => true
    }]
  }]
}
end

def post(url, payload)
  uri = URI.parse(url)
  http = Net::HTTP.new(uri.host, uri.port)
  http.use_ssl = true
  http.post("#{uri.path}?#{uri.query}", payload.to_json)  
end

options = parse_options(ARGV)
payload = format_payload(options)
url = "#{options.fetch(:slack_url)}?token=#{options.fetch(:token)}"

post(url, payload)

process.monit

check process _process_name_
  with pidfile /path/to/pidfile.pid
  start program = "/path/to/start" as uid _user_ and gid _group_ with timeout 30 seconds
  stop program = "/path/to/stop" as uid _user_ and gid _group_ with timeout 30 seconds
  if does not exist for 1 cycle
    then exec "/path/to/ruby /path/to/post_to_slack.rb --service _process_name_ --status error --text 'Process X is down'"
    else if succeeded for 1 cycle then exec "/path/to/ruby /path/to/post_to_slack.rb --service _process_name_ --status ok --text 'Process X is up'"
  group _process_group_