A More Courteous Unicorn Worker Assassin

config.ru

require 'sinatra'

require_relative 'otel.conf.rb'

require 'rack-timeout'
use Rack::Timeout,
  service_timeout: 15, # shorter than unicorn's timeout!
  term_on_timeout: false # TERM prevents at_exit()

require './unreliable_app'
run UnreliableApp

Gemfile

source 'https://rubygems.org'
gem 'unicorn'
gem 'rack-timeout'
gem 'sinatra'
gem 'opentelemetry-sdk'
gem 'opentelemetry-exporter-otlp'
gem 'opentelemetry-instrumentation-all'

otel.conf.rb

require 'opentelemetry/sdk'
require 'opentelemetry/exporter/otlp'
require 'opentelemetry/instrumentation/sinatra'

##
# A module to represent how an organization might wrap and customize
# observability configuration.
#
module O11yWrapper
  ##
  # Standard minimal OTel SDK configuration.
  #
  OpenTelemetry::SDK.configure do |c|
    c.service_name = 'unreliable_app'
    c.use_all() # enables all instrumentation!
  end

  ##
  # flag to mark that we've been told to put the chairs up and turn out the lights
  #
  @@shutting_down = false

  ##
  # Call to make a best effort at shipping closed and queued telemetry data out of
  # the process and off to backends.
  #
  def self.export_hail_mary
    unless @@shutting_down
      @@shutting_down = true
      case OpenTelemetry.tracer_provider.shutdown(timeout: 5)
      when OpenTelemetry::SDK::Trace::Export::SUCCESS ; puts "🔭 Span export successful. 🚀"
      when OpenTelemetry::SDK::Trace::Export::FAILURE ; puts "🔭 Span export failed. 🤷"
      when OpenTelemetry::SDK::Trace::Export::TIMEOUT ; puts "🔭 Span export timed out. ⌛️"
      end
      puts "🦄💬 'I did what I could.' 🫡"
    end
  end
end

##
# Gentler process exits will be handled with an at_exit.
#
at_exit do
  puts "🔭 Exiting. 🧹 Cleaning up."
  O11yWrapper.export_hail_mary
end

Tiltfile

local_resource('unreliable app',
    serve_cmd='unicorn --config-file unicorn.conf.rb',
    deps=[
        'Gemfile.lock',
        'unicorn.conf.rb',
        'otel.conf.rb',
        'config.ru',
        'unreliable_app.rb',
        ],
    links=[
        link('http://localhost:8080/', 'GET'),
        link('http://localhost:8080/sleepy?nap_seconds=10', 'SLEEPY GET'),
    ]
)

# go install github.com/CtrlSpice/otel-desktop-viewer@latest
# it's pretty dope!
local_resource('trace viewer',
    serve_cmd='$(go env GOPATH)/bin/otel-desktop-viewer',
    links=[link('http://localhost:8000/', 'View Traces')]
)

local_resource('poke',
    cmd='curl localhost:8080',
    auto_init=False
)

local_resource('sleepy poke',
    cmd='curl localhost:8080/sleepy?nap_seconds=5',
    auto_init=False
)

local_resource('too sleepy poke',
    cmd='curl localhost:8080/sleepy?nap_seconds=20',
    auto_init=False
)

local_resource('update gems',
    cmd='bundle install',
    auto_init=False,
    deps=['Gemfile']
)

unicorn.conf.rb

worker_processes 2
timeout 20 # longer than rack-timeout!

unreliable_app.rb

require 'sinatra/base'
require 'opentelemetry/sdk'

class UnreliableApp < Sinatra::Base
  AppTracer = OpenTelemetry.tracer_provider.tracer('unreliable')

  def compute_dynamism
    AppTracer.in_span('compute_dynamism') do
      rand(36**6).to_s(36)
    end
  end

  get '/' do
    dynamism = compute_dynamism
    "<p>Randomness: #{dynamism}"
  end

  get '/sleepy' do
    dynamism = compute_dynamism
    puts "🥱 Maybe I could use a nap ..."
    nap_seconds = params['nap_seconds'] || 1
    AppTracer.in_span('napping', attributes: {"nap_seconds" => nap_seconds}) do
      sleep nap_seconds.to_i
    end
    "<p>I had to sleep for a bit (#{nap_seconds} seconds). Randomness: #{dynamism}"
  end
end