An example of a rake task for re-uploading the aws files.

aws_s3_reupload.rake

namespace :s3_files do

  desc 'Reuploads the s3 files from the old locations'
  task :reupload => :environment do

    ok = 0
    not_ok = 0
    puts ' ', '-----', 'Re-uploading User avatars'
    User.where('avatar IS NOT NULL').each do |user|
      new_path = "uploads/user/#{user.uuid.to_s}/avatar"
      old_path = "public/user/#{user.uuid.to_s}/avatar"

      # url of the file with the old path
      source_url = user.avatar.url.gsub(new_path, old_path)
      source_file_reachable = file_reachable? source_url

      if source_file_reachable
        # url of the new file; 
        # nil unless the rake task is being successfully run again
        target_url = user.avatar.url

        # if the task is repeated, only unprocessed files should be processed
        target_file_not_saved = !file_reachable?(target_url)

        if target_file_not_saved
          begin
            user.cropping = true
            user.remote_avatar_url = source_url
            user.save!
            ok += 1
          rescue Exception => e
            puts "Exception re-uploading file: #{source_url}", e.inspect
            not_ok += 1
          end
        end
      else
        puts "Source file: #{source_url} not reachable"
        not_ok += 1
      end
    end
    puts "#{ok} files successfully re-uploaded" unless ok == 0
    puts "#{not_ok} files not re-uploaded" unless not_ok == 0

  end

  def file_reachable?(url)
    uri = URI(url)

    request = Net::HTTP.new uri.host
    response = request.request_head uri.path
    response.code.to_i == 200
  end

end