Task to precompile assets locally using Capistrano based on http://www.rostamizadeh.net/blog/2012/04/14/precompiling-assets-locally-for-capistrano-deployment and http://p373.net/2013/05/14/rails-deployments-from-4-minutes-to-40-seconds/

deploy.rb

# Taken from http://www.rostamizadeh.net/blog/2012/04/14/precompiling-assets-locally-for-capistrano-deployment
# If we use asset_sync /CDN or maintenance page, try this instead
# http://p373.net/2013/05/14/rails-deployments-from-4-minutes-to-40-seconds/

before 'deploy:finalize_update', 'deploy:assets:symlink'
after 'deploy:update_code', 'deploy:assets:precompile'

namespace :deploy do
  namespace :assets do

    task :precompile, :roles => :web do
      from = source.next_revision(current_revision)
      if capture("cd #{latest_release} && #{source.local.log(from)} vendor/assets/ lib/assets/ app/assets/ | wc -l").to_i > 0
        run_locally("rake assets:clean && RAILS_ENV=production bundle exec rake assets:precompile")
        run_locally "cd public && tar -jcf assets.tar.bz2 assets"
        top.upload "public/assets.tar.bz2", "#{shared_path}", :via => :scp
        run "cd #{shared_path} && tar -jxf assets.tar.bz2 && rm assets.tar.bz2"
        run_locally "rm public/assets.tar.bz2"
        run_locally("rake assets:clean")
      else
        logger.info "Skipping asset precompilation because there were no asset changes"
      end
    end

    task :symlink, roles: :web do
      run ("rm -rf #{latest_release}/public/assets &&
            mkdir -p #{latest_release}/public &&
            mkdir -p #{shared_path}/assets &&
            ln -s #{shared_path}/assets #{latest_release}/public/assets")
    end
  end
end