Sinatra and Heroku tips

While building this site I read several useful articles that promoted best practices for Sinatra and Heroku. What follows are fairly raw tips and code snippets that I found useful and might be handy for you.

Use Bundler for your gems

Some of the older Heroku documentation suggests using a .gems file. At the time of writing, best practice is to use Bundler:

$ sudo gem install bundler

Create a file called Gemfile in your application root:

source :gemcutter
gem 'sinatra'
# add any other gems you need here

Then run:

$ bundle install

Don’t forget to add the Gemfile and Gemfile.lock to your repo:

$ git add Gemfile Gemfile.lock
$ git commit -m "Adding Gemfile and Gemfile.lock for Bundler."

When you come to deploy your application Heroku will pick these files up and install any dependencies your application needs. Magic.

Further information is in the Heroku Bundler article.

Use memcached to store page content

In your configure block add the following:

configure do
  ...
  require 'memcached'
  CACHE = Memcached.new
  ...
end

Then in actions where you want to save the content:

get '/' do
  begin
    content = CACHE.get("home")
  rescue Memcached::NotFound
    content = erb(:home)
    CACHE.set("home", content)
  end
  content
end

You’ll need to make sure you have a local Memcached instance running while developing. I leave this running in a Terminal window via memcached -vv to get verbose debugging output.

Use Heroku’s Varnish caching

Heroku includes a built-in server-side page cache. If you set HTTP headers in your response then Varnish will do the rest. I’ve set up a simple helper for this:

helpers do
  ...
  def cache_for(mins = 1)
    if settings.environment != :development
      response['Cache-Control'] = "public, max-age=#{60*mins}"
    end
  end
  ...
end

Because browsers also pick up on these cache directives you get the double benefit of your visitors’ browsers caching pages, plus the server.

I don’t want the caching to kick in when developing, however, so only do this when not in development mode.

Escape variables output in HTML

When outputting content, especially anything entered by a user, it’s best to escape it to prevent malicious users stealing cookies or other bad behaviour. In your controller, include the following in your helpers block:

helpers do
  ...
  include Rack::Utils
  alias_method :h, :escape_html
  ...
end

Then, in your view, you can escape any variable as follows:

<p><%= h @my_potentially_naughty_variable %></p>

Use UTF-8

You want to use UTF-8 right?

Save your pages as UTF-8, whenever you can.

–W3C Internationalization tutorial

Add this before block and forget about it:

before do
  ...
  headers "Content-Type" => "text/html; charset=utf-8"
  ...
end

Miscellany

Other useful things I found: