An introduction to Feature Flags, canary deployments and finally, Swivel: A PHP library that will manage cohorts and features automatically for the developer.

1. FEATURE FLAGS ARE
FLAWED
LET'S MAKE THEM BETTER
Created by Stephen Young / @young_steveo

3. FEATURE FLAG?
I've seen a lot of names for this concept tossed
around: feature bits, ags, ippers, switches
and the like. There seems no generally
accepted name yet.
— Martin Fowler

4. SIMPLE TOGGLE
class AmazingRecipe {
public function getSauce() {
$useNewRecipe = false;
// $useNewRecipe = true;
if ($useNewRecipe) {
// new formula here
} else {
// original code here
}
}
}

5. TRADITIONAL
FEATURE FLAGS ARE…
FLAWED
...ACTUALLY PRETTY USEFUL AND NOT REALLY FLAWED PER SE, BUT THEY COME WITH A FEW
CHALLENGES AND I THINK WE CAN IMPROVE THE MODEL, SO
LET'S MAKE THEM BETTER

6. SIMPLE TOGGLE
class AmazingRecipe {
public function getSauce() {
$useNewRecipe = false;
// $useNewRecipe = true;
if ($useNewRecipe) {
// new formula here
} else {
// original code here
}
}
}
❌
❌
Not Testable

7. SIMPLE TOGGLE V2
class AmazingRecipe {
public function getSauce() {
if ($this->useNewRecipe()) {
// new formula here
} else {
// original code here
}
}
public function useNewRecipe() {
return false; // true
}
}
←
←
Can Be Stubbed

8. MOCK TOGGLE
/**
* @dataProvider newFormulaProvider
*/
public function testGetSauce($useNew, $sauce) {
$sut = $this->getMock('AmazingRecipe', ['useNewRecipe']);
$sut->expects($this->once())
->method('useNewRecipe')
->will($this->returnValue($useNew));
$this->assertEquals($sauce, $sut->getSauce());
}
public function newFormulaProvider() {
return [
[ false, 'old Recipe' ],
[ true, 'new Recipe' ]
];
}

9. SIMPLE TOGGLE V2
class AmazingRecipe {
public function getSauce() {
if ($this->useNewRecipe()) {
// new formula here
} else {
// original code here
}
}
public function useNewRecipe() {
return false; // true
}
}
❌❌❌
Not Maintainable
Not Con gurable
Not My Concern

10. FEATURE ROUTER
class AmazingRecipe {
public function getSauce() {
if ($this->useNewRecipe()) {
// new formula here
} else {
// original code here
}
}
public function useNewRecipe() {
return Flags::enabled('AmazingRecipie.NewSauceFormula');
}
}

11. FEATURE ROUTER
final class Flags {
protected static $map = [];
public static function enabled($key) {
if (empty(static::$map)) {
// hydrate map
}
return !empty(static::$map[$key]);
}
}

12. TRADITIONAL FEATURE FLAG SYSTEM
Curb Long-Lived Feature Branches
Easy To Use (If This Then That)
Testable
Tons of Applications
Continuous Delivery
Timed Releases
Operations Toggles

13. WHAT'S NOT TO LIKE?

14. CYCLOMATIC COMPLEXITY
public function getSauce() {
if ($this->useNewRecipe()) {
if ($this->testSpicyVersion()) {
// add spice
}
if ($this->fixEnabled()) {
// fix bug in new code
}
} else {
// original code here
if ($this->fixEnabled()) {
// fix bug in old code
}
}
}
Complexity: 5

15. ALL OR NOTHING

16. CANARY DEPLOYMENTS

17. COHORTS
[…] a cohort is a group of subjects who have
shared a particular event together during a
particular time span.
— Wikipedia

18. MORE CONDITIONS?
if (
Flags::enabled('SomeFeature') &&
$user->canSeeFeature('SomeFeature')
) {
// execute feature code
}
class User {
public function canSeeFeature($feature) {
// check the db or user session?
}
}

19. INTRODUCING SWIVEL
Swivel can enable features for a subset of users.
No more complex control ow; Swivel takes care of
determining code paths.

20. BASIC CONCEPTS
1. Segment users into 10 cohorts. Swivel calls these Buckets.
2. Associate a Feature to a number of active Buckets.
3. Write code that runs when a particular Feature is enabled.
4. Group Features under common Parent Feature to toggle
multiple at once.
NewExperience
NewExperience.NavLinks
NewExperience.Dashboard
NewExperience.Pro le

21. SEGMENT USERS INTO BUCKETS
id user_id bucket_id
1 160 6
2 956 2
3 189 7
4 412 2

22. ASSOCIATE FEATURES TO BUCKETS
id slug buckets
1 "AwesomeSauce" "1,2,3,4"
2 "AwesomeSauce.Spicy" "1,2"
3 "AwesomeSauce.Saucy" "3,4"

23. BOOTSTRAP
$bucket = 5; // From Session or DB
$map = [
'AwesomeSauce' => [1,2,3,4],
'AwesomeSauce.Spicy' => [1,2],
'AwesomeSauce.Saucy' => [3,4]
];
$config = new ZumbaSwivelConfig($map, $bucket);
$swivel = new ZumbaSwivelManager($config);

24. TOGGLE EXAMPLE
class AmazingRecipe {
public function __construct(ZumbaSwivelManager $swivel) {
$this->swivel = $swivel;
}
public function getSauce() {
return $this->swivel->forFeature('AwesomeSauce')
->addBehavior('Spicy', [$this, 'getSpicyFormula'])
->addBehavior('Saucy', [$this, 'getSaucyFormula'])
->defaultBehavior([$this, 'getFormula'])
->execute();
}
protected function getSpicyFormula() { }
protected function getSaucyFormula() { }
protected function getFormula() { }
}

25. METRICS FOR CANARY DEPLOYMENTS

26. SWIVEL LOGGING
PSR-3 LOGGER AWARE
$config = new ZumbaSwivelConfig($map, $bucket, $psr3Logger);
// or
$config->setLogger($psr3Logger);

27. SWIVEL METRICS
STATSD STYLE METRICS INTERFACE
interface MetricsInterface {
public function count($context, $source, $value, $metric);
public function decrement($context, $source, $metric);
public function endMemoryProfile($context, $source, $metric);
public function endTiming($context, $source, $metric);
public function gauge($context, $source, $value, $metric);
public function increment($context, $source, $metric);
public function memory($context, $source, $memory, $metric);
public function set($context, $source, $value, $metric);
public function setNamespace($namespace);
public function startMemoryProfile($context, $source, $metric);
public function startTiming($context, $source, $metric);
public function time($context, $source, Closure $func, $metric);
public function timing($context, $source, $value, $metric);
}

28. METRICS FOR A/B TESTING

29. COMPLEXITY

30. TRADITIONAL FEATURE FLAGS
PROS
Eliminate Long Lived Branches
Disable Problematic Code
CONS
Complexity Bump
All Or Nothing

31. COHORT FEATURE FLAGS
PROS
Eliminate Long Lived Branches
Disable Problematic Code
Roll Out Features
A/B Testing
CONS
Complexity Bump
All Or Nothing

32. SWIVEL FEATURE FLAGS
PROS
Eliminate Long Lived Branches
Disable Problematic Code
Roll Out Features
A/B Testing
Built In Logging
Built In Metrics
CONS
Complexity Bump

33. QUESTIONS?

34. GO FORTH AND TOGGLE!
Twitter: @young_steveo
Lanyrd: http://lanyrd.com/2016/syntaxcon/sfbqxr
Swivel: https://github.com/zumba/swivel
Swiveljs: https://github.com/zumba/swiveljs
Swivel Cake: https://github.com/zumba/swivel-cake
THANKS!