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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