Feature Bits at LSSC10

Feature Bits:
Enabling Flow
Within and Across Teams

Erik Sowa and Rob Loh
LSSC10 (April 2010)

Thursday, May 27, 2010

Outline of Talk

• Business context
• Continuous flow of code
• Latent code: Introducing feature bits
• Lyris' implementation (Rob Loh)
• Lessons learned


Invitation...


Business Context


Enable Flow: Avoid Big Bangs

Photo Credit: USDOE (http://commons.wikimedia.org/wiki/File:Castle_romeo2.jpg)


Deployment Pipeline

Photo Credit: Ryan McFarland (http://commons.wikimedia.org/wiki/File:Alaska_Pipeline.jpg )


Continuous Delivery

Documented examples:

• Allspaw, John and Hammond, Paul,
10+ Deploys Per Day: Dev and Ops Cooperation at Flickr
http://en.oreilly.com/velocity2009/public/schedule/detail/7641
http://www.slideshare.net/jallspaw/10-deploys-per-day-dev-and-ops-cooperation-at-flickr
http://velocityconference.blip.tv/file/2284377/

• Humble, Jez and Farley, David,
Continuous Delivery (O'Reilly Rough Cuts)
• What about features you can't build in a day?


Feature Bits: Latent Code

Photo Credit: Marcin Wichary (http://commons.wikimedia.org/wiki/File:IMSAI8080_TV11.jpg)

Latent code variants

• DigitalRiver and ExactTarget
o "Feature bits" used by Sean G. Ryan and team
• Flickr
o Previously cited talk mentions "feature flags"
o http://en.oreilly.com/velocity2010/public/schedule/detail/14145
• Twitter
o "dynamically controlling features" and "infrastructure"
o http://nosql.mypopescu.com/post/407159447/cassandra-twitter-an-interview-with-
ryan-king
• Google ???
o Gradual rollout of new features
• Etc.


Usage at Lyris
• Introduced August, 2008
• ~ 80 active bits by December, 2009
• 48 active bits in March, 2010

Photo Credit: superde1uxe (http://commons.wikimedia.org/wiki/File:IMSAI8080.jpg)


Our implementation

• Rob Loh


Feature Bits

Technical Details


Outline
Implementation
Context
Requirements
Model
API
Discovery

Coding Patterns
Simple
By Design

Closing Points


Implementation


Context

Requirements

• 3 levels of granularity: Global, Org, User-Org Account
• Absence of a feature or any bits means that feature is off
• Consistent list across our shared environments
• Simple checks from the Flex tier, and the services tier
• Simple process to register new features
• In general, keep it simple for adoption and because of our
internal diversity.


Data Model

Flex: Embedded in the bootstrap
<features>
<feature name="hq.remote_panel_load" />
<feature name="el.enable_asset_library" />
...etc...
</features>

Flex: Simple X-Path implementation

public function isFeatureOn(featureName:String):Boolean {
   var nodes:XMLList = xml.features.feature.
       (@name==featureName);
   return null != nodes && 0 < nodes.length();
}

Core Service API
${core-url}/accounts/featureBits?userUid=&orgUid=&


Coding Patterns


Generalized / Meta-data
{ sectionName: "Mobile Marketing",
links: [ { app:"EmailLabs", type:"panel",
panelClass:"smssubscribers",
featurebit:"el.enable_sms_messages" },
//...

Basic Checks
if( registry.config.isFeatureOn( featureName ) ) {
// new implementation ...
} else {
// the old way ...

Cached
public function onInitialize():void {
featureAIsOn = registry.config.isFeatureOn
( featureA );


Use with Strategy pattern:
if( registry.conﬁg.isFeatureOn("ct.analyzer.v2") ) {
service.analyzer = new Analyzer2();
} else {
    service.analyzer = new Analyzer();
}

Use with Factory pattern:
public function createMainDisplay():DisplayObject {
if( registry.config.isFeatureOn( "service.panel.v2" ) ) {
return new panel2(); // which extends panel
} else {
return new panel(); // which extends DisplayObject
}
}

Use with Chain of Responsibility pattern:
if( registry.config.isFeatureOn("hq.trickle_reporting") ) {
   userActionLogger = userActionLogger.setNext(
       new TrickleReportNotiﬁer( .. )
    );
}


Closing Points

• Assess the need for feature-bit protections early.
• Employ a naming system so as to prevent collision between
teams. Avoid re-using names.
• Ensure QA understands the intended state of bits for the
code in production.
• Some teams have used feature-bits to demonstrate bug
fixes during Sprint Reviews. Be careful with this pattern.
• Multiple code paths will need support/maintenance for as
long as a "feature" is in the system.
• Create stories/work items for retiring feature bit protection
for any work requiring them, at the time that work is
happening.
• Ensure old code is retired as well as protections removed.


Lessons Learned

Photo Credit: Underwood & Underwood (http://commons.wikimedia.org/wiki/File:Ecuadoran_Students.jpg)


Design Pressure is Good

Photo Credit: Tokino (http://commons.wikimedia.org/wiki/File:Air_pressure_gauge.jpg)

Manage the Lifecycle

Photo Credit: Pyrothansia (http://commons.wikimedia.org/wiki/File:Life_cycle.jpg)


Maintain Production Quality

Code hidden behind feature bits
is subject to the same quality
requirements as any code

Photo Credit: Rjgdoy (http://commons.wikimedia.org/wiki/File:Quality_not_quantity.png)


Default state: Decouple code rolls

Photo Credit: Kazumasa Ogawa (http://commons.wikimedia.org/wiki/File:Japanese_Chain_coupler.jpg)

Naming Convention Matters


Do Not Overload

Photo Credit: Jonathan Mallard
(http://commons.wikimedia.org/wiki/File:Unsafe_transport_of_a_shipping_container_in_Afghanistan.jpg)


Customer-facing releases


Limit the overhead

Photo Credit: Henning Klevier (http://commons.wikimedia.org/wiki/File:Fibonacci_%28x%2B1%29%5En.png)


Beta- and Split-Testing

Photo Credit: US Navy (http://commons.wikimedia.org/wiki/File:Navy_binoculars.jpg)

Q&A


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