rake & delayed jobs

Signed-off-by: Yury Kaliada <fut.wrk@gmail.com>

Author: FUT

notes/19 - rake & delayed jobs.md

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+# Rake
+## Standalone
+
+Rake is a Make-like program implemented in Ruby. Tasks and dependencies are specified in standard Ruby syntax.
+
+### Default task
+```
+task default: %w[hello]
+
+task :hello do
+  puts 'Hi!'
+end
+
+task :multiply do
+  puts 123 * 2
+end
+
+```
+
+```
+rake
+rake hello
+rake multiply
+```
+
+### Namespace
+```
+  namespace :morning do
+    task :turn_of_alarm
+    ....
+  end
+```
+
+### Invoke task
+```
+  namespace :afternoon do
+    task :make_coffee do
+      Rake::Task['morning:make_coffee'].invoke
+      puts "Ready for the rest of the day!"
+    end
+  end
+  ```
+
+## With Rails
+
+### Useful tasks
+```
+rake -T
+
+rake db:create                       
+rake db:drop                           
+rake db:migrate
+rake db:migrate:status
+rake db:rollback
+rake db:seed
+rake middleware
+rake notes
+rake routes
+rake secret
+rake stats
+rake test
+rake assets:precompile
+```
+
+### Files
+```
+Rakefile
+lib/tasks/*.rake
+```
+
+### Custom rake task
+
+```
+namespace :my do
+  desc "This task does nothing"
+  task :nothing do
+    # Seriously, nothing
+  end
+end
+```
+
+```
+rake -T
+```
+
+# Background jobs Jobs
+
+## Delayed Job
+
+* One thread per process
+* Stores tasks in the relational database
+
+## Resque
+
+* One thread per process
+* Stores tasks in Redis
+
+## Sidekiq
+
+* Multiple threads per process
+* Stores tasks in Redis
+* Web interface
+
+# Sidetiq
+
+* Recurrent jobs
+* Icecube problems
+* Do not use
+
+
+## Create worker
+```
+class HardWorker
+  include Sidekiq::Worker
+  def perform(name, count)
+    # do something
+  end
+end
+```
+
+## Call worker
+```
+HardWorker.perform_async('bob', 5)
+HardWorker.perform_in(5.minutes, 'bob', 5)
+User.delay.do_some_stuff(current_user.id, 20)
+```
+
+## Retries
+
+```
+class LessRetryableWorker
+  include Sidekiq::Worker
+  sidekiq_options :retry => 5 # Only five retries and then to the Dead Job Queue
+
+  def perform(...)
+  end
+end
+```
+
+## Main notes
+
+* Make your job idempotent and transactional
+* Make sure to configure retries
+
+## Web UI
+
+```
+gem 'sinatra', :require => nil
+
+require 'sidekiq/web'
+mount Sidekiq::Web => '/sidekiq'
+```
+
+```
+<%= link_to 'Monitoring', sidekiq_web_path %>
+```
+
+```
+# config/routes.rb
+authenticate :user, lambda { |u| u.admin? } do
+  mount Sidekiq::Web => '/sidekiq'
+end
+```
+
+# Whenever
+
+* Cron humanized api
+* Custom jobs
+* After 25 retries your job will go to dead queue
+* After 6 month job will be discarded
+
+
+BAD:
+```
+every 3.hours do
+  runner "MyModel.some_process"
+  rake "my:rake:task"
+  command "/usr/bin/my_great_command"
+end
+
+every 1.day, :at => '4:30 am' do
+  runner "MyModel.task_to_run_at_four_thirty_in_the_morning"
+end
+
+```
+
+GOOD:
+```
+job_type :sidekiq, "export PATH=your_path:$PATH; cd /var/www/unicorn/current && RAILS_ENV=#{environment} bundle exec sidekiq-client :task :output"
+
+every 3.minutes, :roles => [:app] do
+  sidekiq "-q queue1 push Cache::LiveWorker"
+end
+
+```