Creating a World-Class RESTful Web Services API

Creating a World-Class By David Keener http://www.keenertech.com RESTful Web Services API [email_address]

But First, Who Am I? Blog: http://www.keenertech.com (New Rails-based version in late June) Email: [email_address] David Keener I’m a technical architect and writer with over 20 years of experience. Been doing web applications Since 1997, and Rails applications since version 1.1. I’m a Technical Architect for Grab Networks , the company known for streaming the Beijing Olympics over the web and for distributing more news videos in the US than any other company except MSNBC.

Overview One Minute RESTful Refresher Why would you want a RESTful API? Basic design steps for an API API Architecture Details Scalability Practical Tips I’m talking about the practical experiences gained from creating a real, RESTful Web Services API for use by external customers.

What’s the Big Deal? Rails has been RESTful since 1.2…what’s so hard about doing an API? def index @videos = Video.find(:all) respond_to do |wants| wants.xml { render :layout => false, :xml => @videos.to_xml } wants.json { render :layout => false, :json => @videos.to_json } end end

What’s the Big Deal? Rails has been RESTful since 1.2…what’s so hard about doing an API? def index @videos = Video.find(:all) respond_to do |wants| wants.xml { render :layout => false, :xml => @videos.to_xml } wants.json { render :layout => false, :json => @videos.to_json } end end - No Authentication

What’s the Big Deal? Rails has been RESTful since 1.2…what’s so hard about doing an API? def index @videos = Video.find(:all) respond_to do |wants| wants.xml { render :layout => false, :xml => @videos.to_xml } wants.json { render :layout => false, :json => @videos.to_json } end end - No Authentication - No Authorization

What’s the Big Deal? Rails has been RESTful since 1.2…what’s so hard about doing an API? def index @videos = Video.find(:all) respond_to do |wants| wants.xml { render :layout => false, :xml => @videos.to_xml } wants.json { render :layout => false, :json => @videos.to_json } end end - No Authentication - No Authorization - No Error Handling

What’s the Big Deal? Rails has been RESTful since 1.2…what’s so hard about doing an API? def index @videos = Video.find(:all) respond_to do |wants| wants.xml { render :layout => false, :xml => @videos.to_xml } wants.json { render :layout => false, :json => @videos.to_json } end end - No Authentication - No Authorization - No Error Handling No fine control over data elements

What Does Grab Networks Do? Grab Tools Content Ingestion Transcoding Services Catalog Site Provide Video Store Video Distribute Video (with advertising) Short Answer: 60 Million Video Views Per Month 40,000+ Distributors Video Catalog Content Server Advertisers CDN Media Companies

Where Does the API Fit In? Will allow distributors to integrate video content into their sites more effectively Will provide a better platform on which to build our own tools Will facilitate a level of innovation that could not exist before

Washington Times Video content integrated in via RESTful API (Beta)

One-Minute RESTful Refresher HTTP methods are the “verbs” Acting on Resources (“nouns”) Providing a simple, constrained, easy-to-understand interface

Reasons for Doing an API Know WHY you’re doing an API before you embark on creating one. Most reasons fall into two basic categories: Customer-Centric: To better serve customers Company-Centric: To better serve yourself

Customer-Centric Reasons To give customers direct access to content To facilitate innovation by giving customers the capability to leverage your resources for their own purposes To allow customers to explore your content more effectively To allow authorized customers to directly manipulate resources

Company-Centric Reasons To organize functionality in a more manageable, maintainable way To centralize key logic components, e.g. –authorization logic To facilitate the creation of your own tools To leverage the creativity and innovativeness of your customers To promote tighter coupling of customer applications with API, resulting in an enhanced exit barrier

The First Step… All important projects must have a codename Like…. Tiger Leopard Longhorn

The First Step… All important projects must have a codename Like…. Tiger Leopard Longhorn (um, maybe not)

The First Step… All important projects must have a codename Like….

The First Step… All important projects must have a codename Like…. 9

Designing the API Identify the basic objects in your problem domain - These are your candidate resources Identify the relationships between your resources - These help you define nesting Look for “actions” that need to become “nouns” Ex. – subscription ( a standard example) Ex. – Publishing a video results in a “distribution” Stay in Beta a long time…you will make changes Designing a RESTful API is an interesting challenge. Forget your existing database, and start at the logical level…

Reality Sets In Your database wasn’t designed to have a RESTful API built on top of it Your database probably doesn’t support the authorization needs of your API So you’re going to need a massive re-factor (or a series of them) And management will still want you to develop new features during the massive re-factor(s) This is where you compare your nice, clean, elegant resource design with your ugly, grown-over-time database

Need a (Painful) Example? Distributors were people with accounts Users were distributors who had filled out detailed profile information about themselves Two tables… Some objects were owned by distributors Some objects were owned by users Distributors => Users User => Profiles Re-factor to change ownership to users

Anatomy of an API Request Next, we standardized how API requests should work…

Authentication Since there’s no money involved… Basic HTTP Authentication SSL for additional security Using a simple 20-character API key Easily supported in Rails Can add a more advanced scheme later if needed Authentication is the process of identifying who is accessing the API

Three Major Components Acts As Authorized: Handles privilege-checking to determine whether users can view, create, update or delete resources Externalizable: Domain-Specific Language (DSL) for exposing content. Also handles creates/updates in JSON and XML Restful Behaviors: Mini-framework for common controller logic related to manipulating resources

Acts As Authorized Handles most privilege checks for the API Relies on hooks in the model underlying each resource - auth_get_owner: Who “owns” the resource - auth_get_groups: Group sharing of resource - find_authorized: A method that honors privs

Acts As Authorized (2) Users can view any resource they created or that is shared with a group to which they belong Users can update a resource if they have the “update_<resource>” privilege for a group with which the resource is shared There are a few case-by-case restrictions

Acts As Authorized (3) Model Acts As Authorized “ Acts As” Resource Hooks

Restful Behaviors Mini-framework collecting common controller logic Functions as a mix-in for API controllers Developers just need to override key methods to tailor controllers for new resources Centralizes key features like externalizing content, error handling, single-asset privilege checking, etc.

Restful Behaviors (2) Model Controller Restful Behaviors Acts As Authorized “ Acts As” Resource Hooks

Externalizable Provides a Domain-Specific Language (DSL) for externalizing resources Included in models as a mix-in Centralizes functionality for producing output Centralizes processing of incoming XML/JSON Centralizes create/update logic and ensures that only exposed fields can be set Can externalize database columns under different names

Externalizable (2) include Externalizable externalize_model_as “video” externalize_attribute :asset_id, :label => "id", :methods => [:index, :show] externalize_attribute :headline, :label => "title” externalize_attribute :abstract, :label => "summary” externalize_attribute :keywords externalize_attribute :created_at, :methods => [:index, :show] externalize_attribute :updated_at, :methods => [:index, :show]

Overall Architecture Model Externalizable Controller Restful Behaviors Acts As Authorized “ Acts As” Resource Hooks Externalizable Specification

Error Handling HTTP Status Codes HTTP “Warn” Header Ex. - 199 WAS-002: An unauthorized network was specified (the “199” => “Miscellaneous Message”) Error Messages in JSON/XML response Last Resort: The “always_ok” option - Always return 200… (Flash) caller has to parse response to determine success or failure The diversity of technologies used to interact with the API makes it challenging to provide meaningful feedback to callers when errors occur.

Searches Set up searches as Index and Create, so it accepts both GET and POST actions Searches are networks-specific - Can search Grab Networks public content or FOX private content (if authorized) Using Sphinx open source search engine Returns videos, but with extra “confidence”

Scalability Load Balancer in front of multiple Web Servers for the API – Can add servers as needed Separate Web Server in Amazon Cloud for contracted partners…handles file uploads and video transcoding tasks – Can load balance and add servers as needed Searches run against replicate production database – Can add replicates as needed Apache magic as needed Scalability is a process, not a binary condition.

Practical Tips Start small, with a few resources - Work out the kinks, then expand the scope Start with an extended Beta - So you can change the API as needed without annoying users Recognize that a re-factor will be required - Just deal with it Eat your own dog food - It will never be solid unless you use your own API Challenge assumptions - Don’t be afraid to re-evaluate and adjust the API as you go Documentation, documentation, documentation

Resources RESTful Web Services by Leonard Richardson and Sam Ruby, Published by O’Reilly http://wasabi.grabnetworks.com - API is not publically available yet, but the documentation is

Creating a World-Class RESTful Web Services API

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