Silent Running: Dark Launches, Feature Toggles & Avoiding Technical Debt

- Shipping frequent, low-risk, regularly scheduled releases as part of a continuous deployment strategy is widely regarded as a valuable agile practice.
- Achieving continuous deployment nirvana can be a big ask for mobile apps, particularly for iOS where the vagaries of the App Store approval process can lead to unwelcome & unpredictable delays.
- This talk will consider the merits of feature toggles and dark launches and the beneficial impact they can have on your development workflow
- We'll also take a look at a Swift approach to minimising the technical debt inherent in these approaches.

Transcript

1. SILENT RUNNING DARK LAUNCHES, FEATURE TOGGLES & AVOIDING TECHNICAL DEBT
2. KEY THEMES ▸ Continuous delivery - quicker feedback, better quality ▸ Continuous delivery for native mobile apps - LOLWUT ? ▸ DevOps secret sauce: Dark launches & feature toggles ▸ Reshaping your delivery process to reshape your code ▸ How to avoid getting up to your ears in technical debt
3. CONTINUOUS DELIVERY (CD) ▸ Quick feedback is key to Agile. Shapes next steps ▸ Reduced risk via smaller, more frequent releases ▸ Minimises codebase complexity & stale branches ▸ Focus on optimising process for quality/learning ▸ ScrumBan + GitHub + CI + Cloud Platform = ❤
4. CD FOR NATIVE MOBILE APPS - THE GOOD NEWS ▸ Mobile apps often a superset of server backend and client frontend ▸ Continuous delivery dovetails well with server tech stacks & tooling ▸ Apple CloudKit is a notable exception - keep control & roll your own ▸ Implement a server for greater flexibility & separation of concerns
5. CD FOR NATIVE MOBILE APPS - I'M SORRY DAVE... ▸ Apple & Google own the OS, platform and means of distribution ▸ They make the rules & often change them + annual OS updates ▸ App Store review delay breaks the CD model & negates benefits ▸ Unpredictable feedback cycle, opaque platforms, loss of control ▸ Amplifies the complexity & thus the cost of production bug fixes
6. I FIND YOUR LACK OF FAITH IN CONTINOUS DELIVERY FOR NATIVE MOBILE APPS DISTURBING
7. DARK LAUNCHES - FEATURES IN THE AIRLOCK ▸ Release server side & native app logic early prior to surfacing in UI ▸ Exercise new logic/components to gather metrics & de-risk rollout ▸ Leverage MVVM app architecture ViewModels to play new features
8. FEATURE TOGGLES TO THE RESCUE ▸ Conditional activation of app features via static or dynamic config ▸ Not just binary on/off switches - can be complex A/B testing logic ▸ Staggered release, deploy to specific user segments/geographies ▸ Push unfinished feature code to avoid long-lived feature branches ▸ Ensure all deployable features present in App Store release binary
9. FEATURIZE ALL THE THINGS ! ▸ You've got a feature toggle hammer so every feature looks like a nail ▸ Decompose your app structure into loosely coupled atomic features ▸ Play nice with App Store constraints but regain autonomy & control ▸ Quickly address production bugs with fine-grained feature rollbacks ▸ Beneficial impact of featurization on backlog grooming & estimation
10. A/B TESTING TOGGLE A/B VERSIONS OF YOUR MESSAGES MEASURE, LEARN, REPEAT
11. CASE STUDY : IOS @ SPOTIFY ▸ 500 KLOC, 40 iOS devs, 100's of daily commits, millions of users ▸ Only 70% of branches were successfully merged back to master ▸ Sophisticated backend to manage features for users or markets ▸ Small feature teams merging code into master many times a day ▸ Feature driven workflow sees 90% of branches merged to master ▸ Master branch stable no need for release branch - deploy 2x week
12. BUT WITH GREAT POWER COMES GREAT...
13. TECHNICAL DEBT
14. BOILERPLATE, IFDEFS, CONDITIONAL LOGIC - ALL ADDS UP AND POLLUTES YOUR CODEBASE
15. RUNNER ! YOU ARE TERMINATED ▸ Implement clear lifecycle management process for feature toggles ▸ Apply RESTful CRUD semantics for toggle management interactions ▸ Some features may be long-lived. Automate removal of old features ▸ Collect features in meaningful groupings & use to manage lifecycle
16. SWIFT PROTOCOL ORIENTED SOLUTION TO TACKLE TECH DEBT ▸ Provides flexibility & extensibility without bloating codebase ▸ Minimise boilerplate & tight coupling via protocol extensions ▸ Supports feature switching & more complex conditional logic ▸ Uses value types, generics, closures & higher order functions ▸ Implement in a Swift module delivered as dynamic framework
17. PROTOCOLS DEFINE CONTRACTS FOR BEHAVIOURS ▸ 'Togglable' Features - unique identity, status & actions ▸ Feature Contexts - meaningful scope to group features ▸ Feature Predicates - encapsulation of conditional logic ▸ Feature Source - abstraction of toggle status provider
18. PROTOCOL EXTENSIONS IMPLEMENT DEFAULT BEHAVIOURS ▸ Avoids boilerplate, enforces 'DRY', implements 'traits' ▸ More flexible, powerful code sharing than inheritance ▸ Useful hook for extensibility for framework consumer
19. PACHINKO A SWIFT FEATURE TOGGLE FRAMEWORK
20. TOGGLABLE PROTOCOL & EXTENSION public protocol Togglable { var context: FeatureContext {get} var signature: FeatureSignature {get} var featureSource: FeatureSource {get} func featurePredicates() -> [FeaturePredicate]? mutating func bindFeaturePredicates(predicates: [FeaturePredicate]) -> () } public extension Togglable { func shouldExecuteFeature() -> Bool { guard let activeFeature = featureSource.activeFeature(context, signature: signature) else { return false } let activeFeaturePredicates = featurePredicates() return activeFeature.shouldExecute(activeFeaturePredicates) } }
21. GENERIC TOGGLE CONDITION TYPE TO ENCAPSULATE PREDICATES public struct ToggleCondition<T> : FeaturePredicate { public typealias Evaluator = T -> Bool private let subject: T private let evaluator: Evaluator public init(subject: T, evaluator: Evaluator){ self.subject = subject self.evaluator = evaluator } public func evaluate() -> Bool { return evaluator(subject) } }
22. PREDICATE EVALUATION LOGIC SUPPORTS ON/OFF OR CONDITIONAL FEATURES public protocol ConditionalFeature : Feature { func shouldExecute(conditions: [FeaturePredicate]?) -> Bool } public extension ConditionalFeature { public func isActive() -> Bool { return status == FeatureStatus.Active } public func shouldExecute(conditions: [FeaturePredicate]?) -> Bool { guard let predicates = conditions else { return isActive() } return predicates.reduce(isActive()) { (aggregate: Bool, predicate: FeaturePredicate) in return aggregate && predicate.evaluate() } } }
23. FURTHER READING ▸ Martin Fowler: http://martinfowler.com/bliki/FeatureToggle.html ▸ tech.finn.no/2013/06/20/dark-launching-and-feature-toggles/ ▸ Pachinko - Swift Framework: github.com/cloudofpoints/pachinko
24. SILENT RUNNING : DOUGLAS TRUMBULL, 1972 PLANET OF THE APES : FRANKLIN J SHAFFNER, 1968 BLADE RUNNER : RIDLEY SCOTT, 1982 2001 A SPACE ODYSSEY : STANLEY KUBRICK, 1968 STAR WARS : GEORGE LUCAS, 1977 ALIEN : RIDLEY SCOTT, 1979 THUNDERBIRDS ARE GO : DAVID LANE, 1966 THEY LIVE : JOHN CARPENTER, 1988 THE MAN WHO FELL TO EARTH : NICOLAS ROEG, 1976 LOGAN'S RUN : MICHAEL ANDERSON, 1976