Speed up assets:precompile with Rails 3.1/3.2 Capistrano deployment

The idea is that if you don't change your assets you don't need to recompile them each time:

This is the solution that Ben Curtis propose for a deployment with git:

 namespace :deploy do      namespace :assets do        task :precompile, :roles => :web, :except => { :no_release => true } do          from = source.next_revision(current_revision)          if releases.length <= 1 || capture("cd #{latest_release} && #{source.local.log(from)} vendor/assets/ app/assets/ | wc -l").to_i > 0            run %Q{cd #{latest_release} && #{rake} RAILS_ENV=#{rails_env} #{asset_env} assets:precompile}          else            logger.info "Skipping asset pre-compilation because there were no asset changes"          end      end    end  end

Here is another approach based on asset age (https://gist.github.com/2784462) :

set :max_asset_age, 2 ## Set asset age in minutes to test modified date against.after "deploy:finalize_update", "deploy:assets:determine_modified_assets", "deploy:assets:conditionally_precompile"namespace :deploy do  namespace :assets do    desc "Figure out modified assets."    task :determine_modified_assets, :roles => assets_role, :except => { :no_release => true } do      set :updated_assets, capture("find #{latest_release}/app/assets -type d -name .git -prune -o -mmin -#{max_asset_age} -type f -print", :except => { :no_release => true }).split    end    desc "Remove callback for asset precompiling unless assets were updated in most recent git commit."    task :conditionally_precompile, :roles => assets_role, :except => { :no_release => true } do      if(updated_assets.empty?)        callback = callbacks[:after].find{|c| c.source == "deploy:assets:precompile" }        callbacks[:after].delete(callback)        logger.info("Skipping asset precompiling, no updated assets.")      else        logger.info("#{updated_assets.length} updated assets. Will precompile.")      end    end  endend

If you prefer to precompile your assets locally you can use this task:

namespace :deploy do  namespace :assets do    desc 'Run the precompile task locally and rsync with shared'    task :precompile, :roles => :web, :except => { :no_release => true } do      from = source.next_revision(current_revision)      if releases.length <= 1 || capture("cd #{latest_release} && #{source.local.log(from)} vendor/assets/ app/assets/ | wc -l").to_i > 0        %x{bundle exec rake assets:precompile}        %x{rsync --recursive --times --rsh=ssh --compress --human-readable --progress public/assets #{user}@#{host}:#{shared_path}}        %x{bundle exec rake assets:clean}      else        logger.info 'Skipping asset pre-compilation because there were no asset changes'      end    end  endend 

Another interesting approach can be that of using a git hook.For example you can add this code to .git/hooks/pre-commit which checks if there are any differences in the assets files and eventually precompiles them and add them to the current commit.

#!/bin/bash# source rvm and .rvmrc if present[ -s "$HOME/.rvm/scripts/rvm" ] && . "$HOME/.rvm/scripts/rvm"[ -s "$PWD/.rvmrc" ] && . "$PWD/.rvmrc"# precompile assets if any have been updatedif git diff-index --name-only HEAD | egrep '^app/assets' >/dev/null ; then  echo 'Precompiling assets...'  rake assets:precompile:all RAILS_ENV=production RAILS_GROUPS=assets  git add public/assets/*fi

If you decide to use this approach you would probably need to change your config/environments/development.rb adding:

config.assets.prefix = '/assets_dev'

So that while in development you won't serve the precompiled assets.

I've just written a gem to solve this problem inside Rails, called turbo-sprockets-rails3. It speeds up your assets:precompile by only recompiling changed files, and only compiling once to generate all assets. It works out of the box for Capistrano, since your assets directory is shared between releases.

This is much more bulletproof than the solutions that use git log, since my patch analyzes the sources of your assets, even if they come from a gem. For example, if you update jquery-rails, a change will be detected for application.js, and only application.js will be recompiled.

Note that I'm also trying to get this patch merged into Rails 4.0.0, and possibly Rails 3.2.9 (see https://github.com/rails/sprockets-rails/pull/21). But for now, it would be awesome if you could help me test out the turbo-sprockets-rails3 gem, and let me know if you have any problems.

tommasop's solution doesn't work when enabled cached-copy, my modified version:

task :precompile, :roles => :web, :except => { :no_release => true } do  from = source.next_revision(current_revision)  if capture("cd #{shared_path}/cached-copy && git diff #{from}.. --stat | grep 'app/assets' | wc -l").to_i > 0    run %Q{cd #{latest_release} && #{rake} RAILS_ENV=#{Rubber.env} #{asset_env} assets:precompile:primary}  else    logger.info "Skipping asset pre-compilation because there were no asset changes"  endend