So you have a nice Rails-app running and you want all your static assets to reside on Amazon S3?

There are other good solutions on the web, but most of what I’ve seen requires that you also use Capistrano for deploying your app. If you have not yet mastered that beast (just like me), you will like this little rake task, that I’ve made.

Just copy/paste this code into your favorite editor, change the 4 parameters in the top, and save it in lib/tasks/aws.rake.

Then you can do this:

# rake aws:sync

This will upload all folders and files from your public folder into your Amazon S3 bucket.

The script creates a file called .aws_cache in the root of your application folder. This is used so that additional calls to rake aws:sync only uploads new and modified files.

If you have already uploaded your files before applying this script, you can start by calling

# rake aws:build_cache

This will build the local cachefiles without uploading anything to Amazon S3.

Here’s the code:

require 'find'
require 'digest/md5'
require 'yaml'

#########################################################
# Configuration - these lines are all you need to edit
ACCESS_KEY_ID     = "your-own-aws-access-key"
SECRET_ACCESS_KEY = "and-the-secret-key"
BUCKET             = "name-of-your-bucket"

# If you have any subfolders inside "public", that you do not want to place on AWS, list them here
IGNORE_FOLDERS    = %w(upload UserFiles videos)
#########################################################

class AwsCache
  def initialize
    @filename = ".aws_cache"
    load
  end

  def clear
    @cache = {}
  end

  def load
    clear
    if File.exists?(@filename)
      @cache = YAML::load_file(@filename)
    end
  end

  def save
    File.open(@filename, "w") do |f|
      f.puts @cache.to_yaml
    end
  end

  def add(path)
    puts "add to cache: #{path}"
    @cache[path] = checksum(path)
  end

  def equal?(path)
    c = checksum(path)
    @cache[path] == c
  end

  protected
  def checksum(path)
    Digest::MD5.file(path).hexdigest
  end
end

namespace :aws do
  desc "Synchronize public folder"
  task :sync => :environment do
    init

    AWS::S3::Base.establish_connection!(
      :access_key_id     => ACCESS_KEY_ID,
      :secret_access_key => SECRET_ACCESS_KEY
    )

    bucket = AWS::S3::Bucket.find(@bucket)

    loop_folder()

    @aws_cache.save
  end

  desc "Rebuild local cache file"
  task :build_cache => :environment do
    init

    absolute_folder = File.join(@base_folder, "")

    Find.find(absolute_folder) do |path|
      if FileTest.directory?(path)
        if File.basename(path)[0] == ?.
          Find.prune
        elsif IGNORE_FOLDERS.include?(File.basename(path))
          Find.prune
        end
      else
        @aws_cache.add(path)
      end
    end

    @aws_cache.save
  end
end

def init
  @base_folder = File.join(RAILS_ROOT, "public")
  @bucket      = BUCKET
  @aws_cache   = AwsCache.new
end

def loop_folder(folder = "")
  absolute_folder = File.join(@base_folder, folder)

  total_size = 0

  Find.find(absolute_folder) do |path|
    if FileTest.directory?(path)
      if File.basename(path)[0] == ?.
        Find.prune
      elsif IGNORE_FOLDERS.include?(File.basename(path))
        Find.prune
      else
        next
      end
    else
      s3_store(path)
    end
  end
end

def s3_store(path)
  s3_path = path.gsub("#{@base_folder}/", '')

  if transfer?(path)
    AWS::S3::S3Object.store(
      s3_path,
      open(path),
      @bucket,
      :access => :public_read)

    puts "Stored into AWS: #{AWS::S3::S3Object.url_for(s3_path, @bucket)[/[^?]+/]}"
  end
end

def transfer?(path)
  return false if @aws_cache.equal?(path)

  @aws_cache.add(path)
  return true
end

Feel free to contact me, if you have any questions, problems, suggestions for improvement.