Building Consistent
RESTful APIs in a High-
Performance Environment
Yegor Borovikov, Software Architect
Brandon Duncan, Director of Engineering
LinkedIn Corporation
http://blog.linkedin.com/

Topics We’ll Cover
> Examples of RESTful APIs
 What’s missing?
 Variety versus Uniformity
> Domain Model as Foundation
 Provides Uniformity
 Allows Flexibility
> Examples of LinkedIn APIs
> Using Incentives to Scale
 Some LinkedIn production APIs metrics
> Q&A
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Examples of RESTful APIs
What if you want to get a person’s profile?
> Use one of these…
http://social.yahooapis.com/v1/user/{guid}/profile
http://api.linkedin.com/v1/people/{guid}
http://www.orkut.com/social/rest/people/{guid}/@self
<?xml version="1.0" encoding="UTF-8"?>
<person>
<id>111222</id>
<first-name>Gertrude</first-name>
<last-name>Stein</last-name>
<headline>Author of Tender Buttons</headline>
<connections total="76">
…
</person>
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Examples of RESTful APIs
What’s Missing?
> Ability to get exactly what you need (variety)
 If you need more, may require multiple
API calls (if they exist)
 If you need less, resources are wasted
> Consistency of responses (uniformity)
 “Same” object returned by different APIs
may have different structure
 Once in production, hard to get consistent later
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Examples of RESTful APIs
Multiple Calls to Get What You Need
> Want to get user’s friend’s profile? Do this…
 http://social.yahooapis.com/v1/user/123/connections
<connections yahoo:start="0" yahoo:count="1" yahoo:total="1">
<connection yahoo:uri="http://social.yahooapis.com/v1/user/123/connection/456?
view=usercard">
<guid>456</guid>
<contactId>4</contactId>
</connection>
</connections>
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Examples of RESTful APIs
Multiple Calls to Get What You Need
> … then make second call to get friend’s profile:
http://social.yahooapis.com/v1/user/456/profile
<profile yahoo:uri="http://social.yahooapis.com/v1/user/456/profile">
<guid>456</guid>
<birthdate>3/3</birthdate>
<created>2008-08-4T17:13:56Z</created>
...
</profile>
 Latent, redundant data
 Optimization requires stickiness
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Typical Solution
Variety versus Uniformity
> Solution: introduce another call
> Desire for variety of responses
undermines uniformity of requests
> Leads to RPC-like REST APIs
> Many APIs + Great Documentation =
Lots of Reading + Lack of Automation
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Domain Model as Foundation
Sample Domain Model
/people : Person[] // collection of Person resources
/id : string // primary key
/name : string
/email : string // unique key
/photo : url
/best-friend : Person
/friends : Person[]
/jobs : Job[] // collection of Job resources
/company : Company
/title : string
/start-date : date
/end-date : date
…
/companies : Company[]
/name : string
/ceo : Person
…
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Domain Model as Foundation
Follow request URL to navigate through your model
> To get a person’s profile:
http://api.linkedin.com/v2/people/123
/people[/id=123]
<person uri=“urn:linkedin:v2:people/123” key=“123”> /id
<id>123</id> /name
<name>Reid Hoffman</name> /email
/photo
<email>reid@linkedin.com</email> /best-friend
<best-friend uri=“urn:linkedin:v2:people/456”/> /friends
… /jobs
/company
</person> /title
/start-date
/end-date
…
 Conventional URL in request /companies
/name
 Default representation in response /ceo
…
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Domain Model as Foundation
Fine-grained Request
> What if you only need certain fields
(e.g., name and photo)?
http://api.linkedin.com/v2/people/123:(name,photo)
<person>
<name>Reid Hoffman</name>
/people[/id=123]
<photo>http://media.linkedin.com/photos/123.jpeg</photo> /id
</person> /name
/email
/photo
/best-friend
/friends
/jobs
/company
/title
/start-date
/end-date
…
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Domain Model as Foundation
Fine-grained Request
> To get names and photos of one’s friends and
their best friends:
…/v2/people/456/friends:(name,photo,best-friend:
(name,photo)) /people[/id=456]
/id
<friends total=“66” start=“0”> /name
<friend uri=“urn:linkedin:v2:people/123” key=“123”> /email
/photo
<name>Reid Hoffman</name> /best-friend
<photo>http://media.linkedin.com/photos/123.jpeg</photo> /friends
<best-friend uri=“urn:linkedin:v2:people/456” key=“456”> /123
/id
<name>Brandon Duncan</name> /name
<photo>http://media.linkedin.com/photos/456.jpeg</photo> /email
/photo
</best-friend> /best-friend
</friend> /name
<friend>…</friend> /photo
/jobs
</friends> …
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Domain Model as Foundation
Fine-grained Request
> Allows client to construct custom calls
> Better than digging for the closest matching API:
http://social...com/v1/user/123/profile
http://social...com/v1/user/123/profile/usercard
http://social...com/v1/user/123/profile/tinyusercard
> Allows optimization on the backend
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Domain Model as Foundation
Benefits
> Provides a frame for both request and response
semantics
> Still allows for flexible syntax
 Requests – path, query params, matrix params…
 Responses – JSON, XML, POJOs, protobuff…
> Helps to unify and automate many development
tasks on both ends
 Request / response creation, parsing, marshalling
 Code (and documentation) generation
 Discovery services
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Examples of LinkedIn APIs
HTTP GET - Read
…/people/email=brandon@gmail.com/friends?sort=name
…/people/123/friends;sort=name:(name,jobs;sort=start-date)
…/people:(id,name,photo)?name=page&company=google
…/people::(123,456)
…/people::(123,456):(name,photo)
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Examples of LinkedIn APIs
HTTP PUT - Update
> Set the user’s name: /people[/id=123]
/id
/name
PUT http://api.linkedin.com/v2/people/123/name /email
<name>Reid Hoffmann</name> /photo
/best-friend
…
> Update the user’s profile - change name and best-
friend and remove photo:
PUT http://api.linkedin.com/v2/people/123
<person> /people[/id=123]
<name>Reid Hoffman</name> /id
/name
<best-friend uri=“urn:linkedin:v2:people/999”/> /email
<photo xsi:nil=“true”/> /photo
</person> /best-friend
…
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Examples of LinkedIn APIs
HTTP POST - Create
> Add a friend /people[/id=123]
/id
POST http://api.linkedin.com/v2/people/123/friends /name
/email
<friend uri=“urn:linkedin:v2:people/888”/> /photo
/best-friend
201 Created /friends
/456
Location: http://api.linkedin.com/v2/people/123/friends/888 /888
…
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Examples of LinkedIn APIs
HTTP DELETE - Remove
> Remove a friend
DELETE http://api.linkedin.com/v2/people/123/friends/456
> Delete a company
DELETE
http://api.linkedin.com/v2/companies/exchange=NYSE&ticker=GM
> Delete two companies
DELETE http://api.linkedin.com/v2/companies::(664,665)
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Use Standard Headers
> Content-Type
> Last-Modified
> Accept
> Vary
> Authorization
> Cache-Control
> Content-MD5
> Location
> Warning
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Incentive System
> Multiple ways to get at the same data
> Partner can ask for exactly what they need
> Associate cost with resources, system of
accounting creates incentives for partners
> Throttling by resource rather than API
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Real-World Example
Xobni Toolbar
> Xobni makes ~20 million profile API calls per week
> Default representation is ~2k on average
> Using in-line filter brings average to ~1.5k
 25% reduction in response size
 ~11000 Mbits savings per day
 11k Mbits out of LinkedIn datacenter
 11k Mbits into Xobni datacenter
 Saves both companies money
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Yegor Borovikov
yborovik@linkedin.com
Brandon Duncan
bduncan@linkedin.com
blog.linkedin.com
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