Fastly Rails Plugin

Fastly dynamic caching integration for Rails.

To use Fastly dynamic caching, you tag any response you wish to cache with unique Surrogate-Key HTTP Header(s) and then hit the Fastly API purge endpoint with the surrogate key when the response changes. The purge instantly replaces the cached response with a fresh response from origin.

This plugin provides three main things:

• Instance and class methods on ActiveRecord (or Mongoid) objects for surrogate keys and purging
• Controller helpers to set Cache-Control and Surrogate-Control response headers
• A controller helper to set Surrogate-Key headers on responses

If you're not familiar with Fastly Surrogate Keys, you might want to check out API Caching and Fastly Surrogate Keys for a primer.

Setup

Add to your Gemfile

gem 'fastly-rails'

Configuration

For information about how to find your Fastly API Key or a Fastly Service ID, refer to our documentation.

Create an initializer for Fastly configuration

FastlyRails.configure do |c|
  c.api_key = ENV['FASTLY_API_KEY']  # Fastly api key, required
  c.max_age = 86400                  # time in seconds, optional, defaults to 2592000 (30 days)
  c.stale_while_revalidate = 86400   # time in seconds, optional, defaults to nil
  c.stale_if_error = 86400           # time in seconds, optional, defaults to nil
  c.service_id = ENV['SERVICE_ID']   # The Fastly service you will be using, required
  c.purging_enabled = !Rails.env.development? # No need to configure a client locally (AVAILABLE ONLY AS OF 0.4.0)
end

Note: purging only requires that you authenticate with your api_key. However, you can provide a user and password if you are using other endpoints in fastly-ruby that require full-auth. Also, you must provide a service_id for purges to work.

Usage

Surrogate Keys

Surrogate keys are what Fastly uses to purge groups of individual objects from our caches.

This plugin adds a few methods to generate surrogate keys automatically. table_key and record_key methods are added to any ActiveRecord::Base instance. table_key is also added to any ActiveRecord::Base class. In fact, table_key on an instance just calls table_key on the class.

We've chosen a simple surrogate key pattern by default. It is:

table_key: self.class.table_key # calls table_name on the class
record_key: "#{table_key}/#{self.id}"

e.g. If you have an ActiveRecord Model named Book.

table key: books
record key: books/1, books/2, books/3, etc...

You can easily override these methods in your models to use custom surrogate keys that may fit your specific application better:

def self.table_key
  "my_custom_table_key"
end

def record_key
  "my_custom_record_key"# Ensure these are unique for each record
end

Headers

This plugin adds a set_cache_control_headers method to ActionController. You'll need to add this in a before_action or after_filter see note on cookies below to any controller action that you wish to edge cache (see example below). The method sets Cache-Control and Surrogate-Control HTTP Headers with a default of 30 days (remember you can configure this, see the initializer setup above).

It's up to you to set Surrogate-Key headers for objects that you want to be able to purge.

To do this use the set_surrogate_key_header method on GET actions.

class BooksController < ApplicationController
  # include this before_action in controller endpoints that you wish to edge cache
  before_action :set_cache_control_headers, only: [:index, :show]
  # This can be used with any customer actions. Set these headers for GETs that you want to cache
  # e.g. before_action :set_cache_control_headers, only: [:index, :show, :my_custom_action]

  def index
    @books = Book.all
    set_surrogate_key_header 'books', @books.map(&:record_key)
  end

  def show
    @book = Book.find(params[:id])
    set_surrogate_key_header @book.record_key
  end
end

Purges

Any object that inherits from ActiveRecord will have purge_all, soft_purge_all, and table_key class methods available as well as purge, soft_purge, purge_all, and soft_purge_all instance methods.

Example usage is show below.

class BooksController < ApplicationController

  def create
    @book = Book.new(params)
    if @book.save
      @book.purge_all
      render @book
    end
  end

  def update
    @book = Book.find(params[:id])
    if @book.update(params)
      @book.purge
      render @book
    end
  end

  def delete
    @book = Book.find(params[:id])
    if @book.destroy
      @book.purge # purge the record
      @book.purge_all # purge the collection so the record is no longer there
    end
  end
end

To simplify controller methods, you could use ActiveRecord callbacks. e.g.

class Book < ActiveRecord::Base
  after_create :purge_all
  after_save :purge
  after_destroy :purge, :purge_all
  ...

end

We have left these out intentially, as they could potentially cause issues when running locally or testing. If you do use these, pay attention, as using callbacks could also inadvertently overwrite HTTP Headers like Cache-Control or Set-Cookie and cause responses to not be properly cached.

Service id

One thing to note is that currently we expect a service_id to be defined in your FastlyRails.configuration. However, we've added localized methods so that your models can override your global service_id, if you needed to operate on more than one for any reason. NOTE: As of 0.3.0, we've renamed the class-level and instance-level service_id methods to fastly_service_identifier in the active_record and mongoid mix-ins. See the CHANGELOG for a link to the Github issue.

Currently, this would require you to basically redefine fastly_service_identifier on the class level of your model:

class Book < ActiveRecord::Base
  def self.fastly_service_identifier
    'MYSERVICEID'
  end
end

Sessions, Cookies, and private data

By default, Fastly will not cache any response containing a Set-Cookie header. In general, this is beneficial because caching responses that contain sensitive data is typically not done on shared caches.

In this plugin the set_cache_control_headers method removes the Set-Cookie header from a request. In some cases, other libraries, particularily middleware, may insert or modify HTTP Headers outside the scope of where the set_cache_control_heades method is invoked in a controller action. For example, some authentication middleware will add a Set-Cookie header into requests after fastly-rails removes it.

This can cause some requests that can (and should) be cached to not be cached due to the presence of Set-Cookie.

In order to remove the Set-Cookie header in these cases, fastly-rails provides an optional piece of middleware that removes Set-Cookie when the Surrogate-Control or Surrogate-Key header is present (the Surrogate-Control header is also inserted by the set_cache_control_headers method and indicates that you want the endpoint to be cached by Fastly and do not need cookies).

fastly-rails middleware to delete Set-Cookie

To override a piece of middleware in Rails, insert custom middleware before it. Once you've identified which middleware is inserting the Set-Cookie header, add the following (in this example, ExampleMiddleware is what we are trying to override`:

# config/application.rb

  config.middleware.insert_before(
    ExampleMiddleware,
    "FastlyRails::Rack::RemoveSetCookieHeader"
  )

Example

Check out our example todo app which has a full example of fastly-rails integration in a simple rails app.

Future Work

• Add an option to send purges in batches.

This will cut down on response delay from waiting for large amounts of purges to happen. This would primarily be geared towards write-heavy apps.

• Your feedback

Testing

First, install all required gems:

$ appraisal install

This engine is capable of testing against multiple versions of Rails. It uses the appraisal gem. To make this happen, use the appraisal command in lieu of rake test:

$ appraisal rake test # tests against all the defined versions in the Appraisals file

$ appraisal rails-3 rake test # finds a defined version in the Appraisals file called "rails-3" and only runs tests against this version

Supported Platforms

We run tests using all combinations of the following versions of Ruby and Rails:

Ruby:

• 1.9.3
• 2.1.1

Rails:

• v3.2.18
• v4.0.5
• v4.1.1

Other Platforms

As of v0.1.2, experimental Mongoid support was added by @joshfrench of Upworthy.

Credits

This plugin was developed by Fastly with lots of help from our friend at Hotel Tonight, Harlow Ward. Check out his blog about Cache Invalidation with Fastly Surrogate Keys which is where many of the ideas used in this plugin originated.

-- This project rocks and uses MIT-LICENSE.