sitemap_generator with Heroku and Amazon S3 problem: Internal server error

1. Add to Gemfile

# in gemfile i have these lines
gem 'sitemap_generator', '2.0.1.pre1'
gem 'carrierwave'
gem 'fog'

2. rake sitemap install.md

bundle install first, and run rake sitemap:install to create a config/sitemap.rb

2. rake sitemap:install

Run `rake sitemap:install` to create a config/sitemap.rb

2. rake sitemapinstall

Run `rake sitemap:install` to create a config/sitemap.rb

3. sitemap.rb

# Set the host name for URL creation
SitemapGenerator::Sitemap.default_host = "http://MYSITE"
SitemapGenerator::Sitemap.sitemaps_host = "http://s3.amazonaws.com/MYBUCKET/"
SitemapGenerator::Sitemap.public_path = 'tmp/'
SitemapGenerator::Sitemap.sitemaps_path = 'sitemaps/'
SitemapGenerator::Sitemap.adapter = SitemapGenerator::WaveAdapter.new

SitemapGenerator::Sitemap.create do
  # Put links creation logic here.
  #
  # The root path '/' and sitemap index file are added automatically for you.
  # Links are added to the Sitemap in the order they are specified.
  #
  # Usage: add(path, options={})
  #        (default options are used if you don't specify)
  #
  # Defaults: :priority => 0.5, :changefreq => 'weekly',
  #           :lastmod => Time.now, :host => default_host
  #
  # Examples:
  #
  # Add '/articles'
  #
  #   add articles_path, :priority => 0.7, :changefreq => 'daily'
  #
  # Add all articles:
  #
  #   Article.find_each do |article|
  #     add article_path(article), :lastmod => article.updated_at
  #   end
  Classroom.find_each do |classroom|
    add classroom_path(classroom), lastmod: classroom.updated_at
  end

  add '/about', changefreq: 'monthly'
  add '/inquiry', changefreq: 'monthly'
  add '/privacy', changefreq: 'never'
  add '/terms', changefreq: 'never'
end

4. carrierwave.rb

# in config/initializers/carrierwave.rb
CarrierWave.configure do |config|
  config.cache_dir = "#{Rails.root}/tmp/"
  config.storage = :fog
  config.permissions = 0666
  config.fog_credentials = {
    :provider               => 'AWS',
    :aws_access_key_id      => ENV['AWS_ACCESS_KEY_ID'],
    :aws_secret_access_key  => ENV['AWS_SECRET_ACCESS_KEY'],
  }
  config.fog_directory  = 'MYBUCKET'
end

5. add AWS S3 idkey to ENV

heroku config:add AWS_ACCESS_KEY_ID=aaaaaa AWS_SECRET_ACCESS_KEY=bbbbbbbbbbbbbbbbb

6. robots.txt

# See http://www.robotstxt.org/wc/norobots.html for documentation on how to use the robots.txt file
#
# To ban all spiders from the entire site uncomment the next two lines:
# User-Agent: *
# Disallow: /
Sitemap: http://s3.amazonaws.com/MYBUCKET/sitemaps/sitemap_index.xml.gz

7. run rake to generate

# test for local
# it should be able to generate xml and upload to S3 if all setup right
export AWS_ACCESS_KEY_ID=aaaaaa
export AWS_SECRET_ACCESS_KEY=bbbbbbbbbbbbbbbbb
rake sitemap:refresh:no_ping

# after pushed to heroku...
# generate sitemap and ping search engines
heroku run rake sitemap:refresh

8. for google webmaster tools

If you use Google Webmaster Tools and want to specify the url of you sitemap, that only allow relative path from your host, you may need to create a route and controller to point to the sitemap xml on the S3.

Further reading:
http://www.billrowell.com/2012/02/01/create-an-xml-sitemap-on-heroku-via-amazon-s3/

Docs:
https://github.com/kjvarga/sitemap_generator
https://github.com/kjvarga/sitemap_generator/wiki/Generate-Sitemaps-on-read-only-filesystems-like-Heroku