capistrano - Why do I need to precompile Rails assets on app servers and not web servers only? -


i'm deploying simple rails app small ubuntu precise64 server setup :
* 1 web server running nginx
* 2 app servers running unicorn
* 1 db server running postgresql

my servers provisionned puppet , i'm pushing app capistrano.

my capfile

load 'deploy' # uncomment if using rails' asset pipeline load 'deploy/assets' load 'config/deploy' # remove line skip loading of default tasks

the deploy.rb file super simple

# execute "bundle install" after deploy, when needed require "bundler/capistrano"  # name of application in scm (git) set :application, "devops-test-app" set :repository, "https://github.com/geoffroymontel/devops-test-app.git" set :scm, :git  set :deploy_to, "/var/www/#{application}"  # server there web server running (nginx) role :web, "172.16.0.2"  # server there db running # rails migrations run role :db, "172.16.0.3", :primary => true  # servers there app servers running (unicorn) role :app, "172.16.0.4", "172.16.0.5"  set :rails_env, :production  # user on server set :user, "deployer" set :use_sudo, false  namespace :deploy    task :start, :roles => :app, :except => { :no_release => true }     run "service unicorn_#{application} start"   end    task :stop, :roles => :app, :except => { :no_release => true }     run "service unicorn_#{application} stop"   end    task :restart, :roles => :app, :except => { :no_release => true }     run "service unicorn_#{application} restart"   end    task :copy_in_database_yml     run "cp #{shared_path}/config/database.yml #{latest_release}/config/"   end    # precompile assets   # have precompile assets on app servers too, , don't know why...   # namespace :assets   #   task :precompile, :roles => [:web, :app], :except => { :no_release => true }   #     run %q{cd #{latest_release} && #{rake} rails_env=#{rails_env} #{asset_env} assets:precompile}   #   end   # end end  before "deploy:assets:precompile", "deploy:copy_in_database_yml"

if don't precompile assets on app servers, application fails.

$ cap roles="app" command="cat /var/www/devops-test-app/current/log/production.log" invoke   * 2013-05-01 21:43:10 executing `invoke'   * executing "cat /var/www/devops-test-app/current/log/production.log"     servers: ["172.16.0.4", "172.16.0.5"]     [172.16.0.5] executing command  ** [out :: 172.16.0.5] connecting database specified database.yml  ** [out :: 172.16.0.5] connecting database specified database.yml  ** [out :: 172.16.0.5] started "/posts" 172.16.0.2 @ 2013-05-01 19:42:10 +0000  ** [out :: 172.16.0.5] processing postscontroller#index html  ** [out :: 172.16.0.5] rendered posts/index.html.erb within layouts/application (25.7ms)  ** [out :: 172.16.0.5] completed 500 internal server error in 122ms  ** [out :: 172.16.0.5]   ** [out :: 172.16.0.5] actionview::template::error (application.css isn't precompiled):  ** [out :: 172.16.0.5] 2: <html>  ** [out :: 172.16.0.5] 3: <head>  ** [out :: 172.16.0.5] 4:   <title>devopstestapp</title>  ** [out :: 172.16.0.5] 5:   <%= stylesheet_link_tag    "application", :media => "all" %>  ** [out :: 172.16.0.5] 6:   <%= javascript_include_tag "application" %>  ** [out :: 172.16.0.5] 7:   <%= csrf_meta_tags %>  ** [out :: 172.16.0.5] 8: </head>  ** [out :: 172.16.0.5] app/views/layouts/application.html.erb:5:in `_app_views_layouts_application_html_erb__677166568443748084_17536100'  ** [out :: 172.16.0.5] app/controllers/posts_controller.rb:7:in `index'

if uncomment commented lines in deploy.rb, fine.

but why ?? thought need compile assets on web server, not on app server.

please me understand why :)

thanks, best regards

geoffroy

because, among other things, rails generates manifest of precompiled assets including hashes of files in filenames, , uses names when include assets in page. when image_url('foo.jpg'), rails end generating foo-b48cf0140bea12734db05ebcdb012f1d265bed84.jpg in source code.

rails needs know compiled names use these assets, has have manifest, precompilation needs done on app server.

take @ public/assets/manifest.yml - that's file rails needs in order serve precompiled assets properly.


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