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2019 DevDay Journey of Feature Flag Development in LINE Android > Hidetsugu Tamaki > LINE App Dev Team3 Software Engineer

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> LINE Android development Hidetsugu Tamaki Introduction > Apr. 2018 ~

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Agenda > Pain Points of Feature Branches > Benefits of Feature Flags > History of Feature Flags in LINE Android

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Agenda > Pain Points of Feature Branches > Benefits of Feature Flags > History of Feature Flags in LINE Android

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Feature Branch Main branch

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Feature Branch Main branch Feature branch

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Feature Branch Main branch Feature branch Pull requests

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Feature Branch Main branch Feature branch Pull requests

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LINE Android Project Developers 100 Changes per week in LoC 20,000

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Feature Branches in Large Applications Main branch Feature branches

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Agenda > Pain Points of Feature Branches > Benefits of Feature Flags > History of Feature Flag in LINE Android

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Feature Flag Strategy Main branch Sticker feature PRs

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Feature Flag Strategy Main branch Sticker feature PRs

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Feature Flag Strategy Main branch Sticker feature PRs

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Feature Flag Usage > View visibility . .

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Feature Flag Usage > Activity I B CG CG ) G E )B = .( . ((. L CG CG G F . = C G I GK B FF I BF L CG CG G F B: = C G I GK B FF I > View visibility FG A E GG C F F B ) G E )B = )( ( ,(

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Conflict Minimization Main branch Sticker feature PRs

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Conflict Minimization Main branch Sticker feature PRs Theme feature PRs

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Conflict Minimization Main branch Sticker feature PRs Theme feature PRs Saved PRs Saved PRs

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Conflict Minimization Main branch Sticker feature PRs Theme feature PRs Conflict Saved PRs Saved PRs

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Smoother Release Schedule Management Main branch Sticker feature PRs

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Smoother Release Schedule Management Main branch Release branches 1.0 Sticker feature PRs

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Smoother Release Schedule Management Main branch Release branches 1.0 Sticker feature PRs

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Smoother Release Schedule Management Main branch Release branches 1.0 2.0 Sticker feature PRs

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Instant Toggling Main branch Release branch 1.0 Sticker feature PR

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✗ Instant Toggling Main branch Release branch 1.0 Critical issue Sticker feature PR

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Instant Toggling Main branch Release branch 1.0 Critical issue Sticker feature PR Conflicting PR ✗

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✗ Instant Toggling Main branch Release branch 1.0 Critical issue Conflicting PR Sticker feature PR

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Better Collaboration with Stakeholders Developer Planner Tester Designer Organization

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Better Collaboration with Stakeholders Developer Planner Tester Designer Users Partners Organization

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Feature Flags Achieve > Conflict minimization > Smoother release schedule management > Instant toggling > Better collaboration with stakeholders

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Limitation of Feature Flags Not a “silver bullet” > Difficult to apply > Updating libraries > Overkill > Prototyping

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Reference https://youtu.be/H81EEAZ4XAI Presented at DroidKaigi 2019 https://speakerdeck.com/line_developers/flag-based-feature-management

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Agenda > Pain Points of Feature Branches > Benefits of Feature Flags > History of Feature Flags in LINE Android

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Feature Flags in LINE Android > Started with a simple Gradle script (Dec. 2015) > Injects values into BuildConfig file > Loads values from a property file

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Feature Flags in LINE Android > Started with a simple Gradle script (Dec. 2015) > Injects values into BuildConfig file A A A C= # . " A A A C= # " #. > Loads values from a property file

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Feature Flags in LINE Android > Started with a simple Gradle script (Dec. 2015) > Injects values into BuildConfig file > Loads values from a property file

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> Toggle flag by user name or app version > Toggle flag at runtime > Support Gradle submodule Growth of Feature Flags

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> Toggle flag by user name or app version > Toggle flag at runtime > Support Gradle submodule Growth of Feature Flags

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Module Structure of LINE Android line-android-app submodule-sticker Product Flavor Product Flavor

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Module Structure of LINE Android line-android-app submodule-sticker Product Flavor Product Flavor dev, beta, rc, release debug, release

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Initial Feature Flags Implementation line-android-app FeatureFlag script Flag Property File Product Flavor Refers to Product Flavor submodule-sticker

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Initial Feature Flags Implementation line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java Injects values into Product Flavor submodule-sticker Refers to

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Misused Feature Flags in Submodules line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script Product Flavor BuildConfig.java submodule-sticker Refers to Injects values into Refers to Injects values into

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Misused Feature Flags in Submodules line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script Product Flavor BuildConfig.java submodule-sticker Back reference Refers to Injects values into Refers to Injects values into

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Misused Feature Flags in Submodules line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script Product Flavor BuildConfig.java dev, beta, rc, release debug, release submodule-sticker Back reference Refers to Injects values into Refers to Injects values into

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Misused Feature Flags in Submodules line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script Product Flavor BuildConfig.java dev, beta, rc, release debug, release submodule-sticker Back reference Refers to Injects values into Refers to Injects values into

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Misused Feature Flags in Submodules line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script Product Flavor BuildConfig.java package com.linecorp.line package com.linecorp.sticker dev, beta, rc, release debug, release submodule-sticker Back reference Refers to Injects values into Refers to Injects values into

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Problems of Misuse > Caused by BuildConfig.java and product flavors > Generated wrong values > Caused by back reference > Submodules were no longer standalone

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Problems of Misuse > Caused by BuildConfig.java and product flavors > Generated wrong values > Caused by back reference > Submodules were no longer standalone

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Workaround for Wrong Flag Values Simplified references by extracting Feature Flags into a module

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Workaround for Wrong Flag Values line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script Product Flavor BuildConfig.java submodule-sticker Back reference Refers to Injects values into Refers to Injects values into

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Workaround for Wrong Flag Values line-android-app FeatureFlag script Flag Property File Product Flavor BuildConfig.java FeatureFlag script feature-flag BuildConfig.java Refers to submodule-sticker Refers to Injects values into Injects values into

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Workaround for Wrong Flag Values BuildConfig.java BuildConfig.java Injects values into Injects values into package com.linecorp.line package com.linecorp.sticker

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Workaround for Wrong Flag Values FeatureFlag.java FeatureFlag.java Creates Creates package com.linecorp.line package com.linecorp.line

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Workaround for Wrong Flag Values line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java FeatureFlag script feature-flag FeatureFlag.java Refers to submodule-sticker Refers to Creates Creates

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Workaround for Wrong Flag Values line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java FeatureFlag script feature-flag FeatureFlag.java Refers to submodule-sticker Refers to Creates Creates

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Workaround for Wrong Flag Values line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java submodule-sticker Refers to Creates

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Things Got Worse > Tricky usage of ` > Wrong dependencies still remain > Poor compatibility with automated testing

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Things Got Worse > Tricky usage of ` > Wrong dependencies still remain > Poor compatibility with automated testing

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Things Got Worse > Tricky usage of ` > Wrong dependencies still remain > Poor compatibility with automated testing

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Things Got Worse > Tricky usage of ` > Wrong dependencies still remain > Poor compatibility with automated testing

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Things Got Worse > Tricky usage of ` > Wrong dependencies still remain > Poor compatibility with automated testing

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Proper Solution Isolated dependencies by processing flags within modules

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Proper Solution line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java submodule-sticker Refers to Creates

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Proper Solution line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java submodule-sticker Refers to FeatureFlag script Flag Property File Product Flavor FeatureFlag.java Refers to Creates Creates

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Flag Property File Product Flavor Proper Solution debug, release

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FeatureFlag.java FeatureFlag.java Proper Solution package com.linecorp.line package com.linecorp.sticker

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Proper Solution line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java submodule-sticker Refers to FeatureFlag script Flag Property File Product Flavor FeatureFlag.java Refers to Links to Creates Creates

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Proper Solution line-android-app FeatureFlag script Flag Property File Product Flavor FeatureFlag.java submodule-sticker Refers to FeatureFlag script Flag Property File Product Flavor FeatureFlag.java Refers to Links to Refers to Creates Creates

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Link to Submodule Flag Values &, - B = B A: &, - &, - line-android-app submodule-sticker

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)& ) ,) () CC )-)& ) = A: )& ) ,) -& ) Property Parsing: Format )& ) ,) () )-)& ) = A: )& ) ,) -& ) > Written with “disjunctive normal form” style property

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Property Parsing: Phase > Enabled if build variant is Phase Phase > Enabled if build variant is

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Property Parsing: Value Calculation : E variant )( ( & ( ( ( ( ( CE A E : CD= : )( ( & ( - ( )( ( & ( D E: C: CE A E : CD= : )( ( & ( - ( F )( ( & ( D E: Optimization Phase resolution

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Property Parsing: Value Calculation : E variant )( ( & ( ( ( ( ( CE A E : CD= : )( ( & ( - ( )( ( & ( D E: C: CE A E : CD= : )( ( & ( - ( F )( ( & ( D E: Optimization Phase resolution

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Property Parsing: Value Calculation : E variant )( ( & ( ( ( ( ( CE A E : CD= : )( ( & ( - ( )( ( & ( D E: C: CE A E : CD= : )( ( & ( - ( F )( ( & ( D E: Optimization Phase resolution

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Property Parsing: Value Calculation : E variant )( ( & ( ( ( ( ( CE A E : CD= : )( ( & ( - ( )( ( & ( D E: C: CE A E : CD= : )( ( & ( - ( F )( ( & ( D E: Optimization Phase resolution

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Property Parsing: Value Calculation )& ) ) () )-)& ) F AC: F E )& ) ) .-& ) )& ) ) F E F AC: F E )& ) ) .-& ) )& ) ) F AC: F E )& ) ) Optimization Variant resolution E F variant Package name extraction I )& ) ) CA CED F E E = )& ) )

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Property Parsing: Value Calculation )& ) ) () )-)& ) F AC: F E )& ) ) .-& ) )& ) ) F E F AC: F E )& ) ) .-& ) )& ) ) F AC: F E )& ) ) Optimization Variant resolution E F variant Package name extraction I )& ) ) CA CED F E E = )& ) )

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Property Parsing: Value Calculation )& ) ) () )-)& ) F AC: F E )& ) ) .-& ) )& ) ) F E F AC: F E )& ) ) .-& ) )& ) ) F AC: F E )& ) ) Optimization Variant resolution E F variant Package name extraction I )& ) ) CA CED F E E = )& ) )

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Property Parsing: Value Calculation )& ) ) () )-)& ) F AC: F E )& ) ) .-& ) )& ) ) F E F AC: F E )& ) ) .-& ) )& ) ) F AC: F E )& ) ) Optimization Variant resolution E F variant Package name extraction I )& ) ) CA CED F E E = )& ) )

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Property Parsing: Value Calculation )& ) ) () )-)& ) F AC: F E )& ) ) .-& ) )& ) ) F E F AC: F E )& ) ) .-& ) )& ) ) F AC: F E )& ) ) Optimization Variant resolution E F variant Package name extraction I )& ) ) CA CED F E E = )& ) )

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Results > Gradle plugin instead of script > Simplified dependencies > Correct feature flag values in submodules

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Results > Gradle plugin instead of script > Simplified dependencies > Correct feature flag values in submodules

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Results > Gradle plugin instead of script > Simplified dependencies > Correct feature flag values in submodules

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Results > Gradle plugin instead of script > Simplified dependencies > Correct feature flag values in submodules

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Available Today > https://github.com/line/feature-flag-android

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Summary > Solved pain points of feature branches with feature flags > Gradle plugin for Android is now available

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Thank You