Improve the build times of your project is not impossible. How we achieved it in N26.

In 2021/2022 N26 android platform team focused on reducing the build times of the project. We achieved to reduce them a 75%! This talk is about how we achieve that successful result that made the N26 Android Engineers happy and more productive.

I will present the implementations that N26 platform team did to reduce the compilation time of our app module from 20-25minuts to 5-6minuts. Also we reduced the compilation time of the library modules to improve the productivity of the engineers. I will talk about the gradle dependency graph, DI (Anvil plugin from square) and about the Dependency Inversion Principle.

Transcript

1. Antoni Castejón
   Improve the build times of your
   project is not impossible.
   How we achieved it in N26
   

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2. Why?
   

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3. STAKEHOLDERS
   👨💻👩💻👨💻👩💻👨💻👩💻👨💻👩💻
   
   👨💻👩💻👨💻👩💻👨💻👩💻👨💻👩💻
   
   👨💻👩💻👨💻👩💻👨💻👩💻👨💻👩💻
   
   👨💻👩💻👨💻👩💻👨💻👩💻👨💻👩💻
   Android Team
   (Product)
   Mobile Core
   👨💻👩💻
   
   👨💻👩💻
   

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4. 😭 ☹ 😶 🙂 🤩
   

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6. It was highly demanded by our
   stakeholders
   

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7. But… It was that painful to work
   with the project?
   

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8. 24 minutes
   Full app build time (./gradlew clean app:assembleDebug)
   🥲
   

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9. The N26 android project
   

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10. core_lib core_lib core_lib
    core_lib
    core_lib core_lib core_lib
    core_lib
    core_lib core_lib core_lib
    core_lib
    core_lib core_lib core_lib
    core_lib
    single_feature_app 1
    feature_app
    feature_lib
    single_feature_app 2
    feature_app
    feature_lib
    single_feature_app 3
    feature_app
    feature_lib
    single_feature_app 4
    feature_app
    feature_lib
    The N26 android project
    Setup before the initiative
    app core libraries folder
    features folder
    

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11. single_feature_app 1
    feature_app
    feature_lib
    The N26 android project
    Single feature apps
    • The feature code
    
    • Runs independently
    
    • Entry point
    
    • Less dependencies
    
    • Less build time
    

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12. feature_app
    The N26 android project
    Single feature apps
    • Login
    
    • Activity entry point
    
    • No production code
    
    • com.android.application
    

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13. feature_lib
    The N26 android project
    Single feature apps
    • Feature code
    
    • Production code
    
    • com.android.library
    

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14. The N26 android project
    Overview before the initiative
    • 312 total modules
    
    • 119 core libraries
    
    • 70 SFAs
    

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15. How?
    

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17. 🙅
    

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18. 🤔
    

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19. Then, what were the issues of the
    project impacting the build time?
    🤔
    

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20. • The Gradle dependency graph
    
    • Legacy monoliths
    

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21. The Gradle dependency graph
    

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22. Chat GPT 3.5
    A visual representation of the dependencies between
    different components in a Gradle-based project. It refers to
    the relationships between different modules, libraries, and
    other dependencies that make up a gradle application.
    The Gradle dependency graph
    

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23. https://github.com/jraska/modules-graph-assert
    

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24. generateModulesGraphStatistics
    

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25. Wikipedia - Glossary of graph theory (https://en.wikipedia.org/wiki/Glossary_of_graph_theory#height)
    The height of a node in a rooted tree is the number
    of edges in a longest path, going away from the
    root, that starts at that node and ends at a leaf.
    

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26. Number of nodes, counting vertically, in
    the path from the root to the last one.
    

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28. 20
    The height of the app module
    

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29. Hypothesis
    

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30. Reducing the height of the graph
    the build time will be reduced
    

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31. To flat the dependency graph
    

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33. Height = 5
    

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35. Height = 2
    

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36. To reduce the height
    

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37. Why?
    

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38. Because of how Gradle build
    works
    

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39. About Gradle
    Parallel execution
    

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40. About Gradle
    Parallel execution
    🔄
    🔄
    🔄
    🔄 🔄
    🔄 🔄 🔄 🔄 🔄
    🔄 🔄
    🔄
    

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41. About Gradle
    Parallel execution
    🔄
    🔄
    🔄
    🔄
    🔄
    🔄 🔄 🔄
    

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42. About Gradle
    Parallel execution
    🔄
    🔄
    🔄
    🔄
    

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43. About Gradle
    Parallel execution
    🔄
    🔄
    🔄
    

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44. About Gradle
    Parallel execution
    🔄
    

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45. About Gradle
    Parallel execution
    🔄
    

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46. About Gradle
    Parallel execution
    

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47. About Gradle
    Executing a gradle task…
    Current execution
    Previous execution
    Skips execution!
    Gradle incremental builds and caching
    Outputs
    Outputs
    

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48. About Gradle
    Gradle incremental builds and caching
    Up-to-date checking
    

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49. About Gradle
    But…
    Current execution
    Previous execution
    Reexecution is needed
    for those tasks
    Gradle incremental builds and caching
    Reexecution is NOT only
    needed for those tasks…
    

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50. About Gradle
    Gradle incremental builds and caching
    Reexecution is NOT only
    needed for those tasks…
    … but also for the
    tasks that depend on
    them
    

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51. About Gradle
    Gradle incremental builds and caching
    

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52. About Gradle
    Gradle incremental builds and caching
    

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53. About Gradle
    Gradle incremental builds and caching
    🔄
    🔄
    🔄
    🔄
    🔄
    

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54. About Gradle
    Gradle incremental builds and caching
    

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55. About Gradle
    Gradle incremental builds and caching
    

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56. About Gradle
    Gradle incremental builds and caching
    🔄
    🔄
    🔄
    

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57. Solution
    

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58. Apply dependency inversion
    Solution proposed for the hypothesis
    • High-level modules should depend on abstractions rather than in low-level
    modules.
    
    • Abstractions should not depend on details. Details should depend on
    abstractions.
    SOLID
    D
    

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59. Apply dependency inversion
    Solution proposed for the hypothesis
    public interface NetworkApi {
    fun connectToInternet()
    fun disconnectFromInternet()
    }
    Abstraction
    public class Network : NetworkApi {
    override fun connectToInternet() {
    // Starting connection...
    }
    override fun disconnectFromInternet() {
    // Disconnecting...
    }
    }
    Details
    

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60. Apply dependency inversion
    Solution proposed for the hypothesis
    High-level modules should depend on abstractions rather than low-
    level modules.
    feature_lib
    details
    feature_lib
    abstraction
    

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61. Apply dependency inversion
    Solution proposed for the hypothesis
    Abstractions should not depend on details. Details should depend
    on abstractions.
    feature_lib
    abstraction
    details
    feature_lib
    abstraction
    details
    

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62. Apply dependency inversion
    Solution proposed for the hypothesis
    Abstraction and details module for
    every potential dependency
    

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63. public class Network : NetworkApi {
    override fun connectToInternet() {
    // Starting connection...
    }
    override fun disconnectFromInternet() {
    // Disconnecting...
    }
    }
    public interface NetworkApi {
    fun connectToInternet()
    fun disconnectFromInternet()
    }
    Apply dependency inversion
    Solution proposed for the hypothesis
    abstraction details
    api core
    

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64. Apply dependency inversion
    Solution proposed for the hypothesis
    core_lib core_lib core_lib
    core_lib
    core_lib core_lib core_lib
    core_lib
    core_lib core_lib core_lib
    core_lib
    core_lib core_lib core_lib
    core_lib
    single_feature_app 1
    feature_app
    feature_lib
    single_feature_app 2
    feature_app
    feature_lib
    single_feature_app 3
    feature_app
    feature_lib
    single_feature_app 4
    feature_app
    feature_lib
    app core libraries folder
    features folder
    core_lib
    

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65. Apply dependency inversion
    Solution proposed for the hypothesis
    core_lib
    api
    core
    

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66. Before dependency inversion
    app
    feature_app
    feature_lib
    core_lib core_lib
    core_lib
    

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67. feature_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    Before dependency inversion
    app
    feature_app
    feature_lib
    core_lib lib
    core_lib
    core_lib
    😭
    

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68. feature_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    Before dependency inversion
    core_lib
    

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69. feature_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    Before dependency inversion
    core_lib
    🔄
    🔄
    🔄
    🔄
    🔄
    🔄
    SEQUENTIALLY
    

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70. With dependency inversion
    app
    feature_app
    feature_lib
    core_lib lib
    core_lib
    api
    api
    api api
    legacy
    app
    feature_app
    feature_lib
    core
    core
    😃
    

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71. With dependency inversion
    app
    feature_app
    feature_lib
    core_lib lib
    core_lib
    api
    api
    api api
    legacy
    app
    feature_app
    feature_lib
    core
    core
    🔄
    

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72. Proof of concept (POC)
    feature_
    fl
    ag
    api
    core
    

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73. 35%
    Build time reduced for a library module (from ~28 to ~18 sec)
    

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74. 76%
    Edges count reduced (from 69 to 17)
    

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75. 56%
    Height reduced (from 9 to 4)
    

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78. What about a feature library?
    

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79. 11%
    build time reduction for our feed library module
    

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80. 1%
    for the app module
    

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81. Process we follow
    Iterative
    Discovery
    Implementation
    Benchmark
    

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82. Process we follow
    Iterative
    Discovery
    Pick the top 5 core
    libraries with:
    ✅ More edges
    ✅ Easy to apply
    Implementation
    Apply DI
    Benchmark
    Compare results:
    master changes
    

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83. Legacy monoliths
    

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84. Chat GPT 3.5
    Monolith: A monolith refers to an application that is built as
    a single, unified unit. All components and features of the
    application are tightly integrated into a single codebase,
    often resulting in a large and complex code structure.
    Legacy monoliths
    

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85. Large single module that does many
    different things
    Legacy monoliths
    

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86. Chat GPT 3.5
    Legacy: Refers to older software systems that are still in use but are no longer
    actively developed or maintained. These systems are usually built using older
    technologies, frameworks, and practices that might not align with modern
    software development trends and best practices. Legacy systems can pose
    challenges in terms of scalability, maintenance, and integration with newer
    technologies.
    Legacy monoliths
    

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87. Old code
    Legacy monoliths
    

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89. What was injectLegacy?
    

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90. Anvil
    

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91. https://github.com/square/anvil
    

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92. Then, why not using Hilt?
    

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93. Anvil VS Hilt
    Anvil
    • Kotlin compiler plugin
    
    • Needs Dagger
    
    • Merges components and
    modules using annotations
    
    • Doesn’t need Kapt
    Hilt
    • Dependency injection framework
    
    • Independent library
    
    • Simpli
    fi
    es Dagger DI for Android
    
    • Needs Kapt
    *
    

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94. Anvil VS Hilt
    Anvil
    • Kotlin compiler plugin
    
    • Needs Dagger
    
    • Merges components and
    modules using annotations
    
    • Doesn’t need Kapt *
    ✅ Without @Component
    
    ✅ Pure Kotlin
    

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95. How was Anvil applied in our
    project?
    

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96. app feature_app
    feature_lib
    feature_lib core
    With Kapt
    No Kapt
    

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97. Then, what was injectLegacy?
    

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98. core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    core_lib
    injectLegacy
    injectLegacy
    BaseComponent
    BaseSessionComponent
    feature_lib
    core_lib
    Legacy monoliths
    app
    

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99. What we did?
    

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100. app
     Legacy monoliths
     injectLegacy
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     injectLegacy
     BaseComponent
     BaseSessionComponent
     feature_lib
     core_lib
     ✅ Removed injectLegacy dependency
     ✅ Add Anvil plugin (if necessary)
     Done by Platform team
     1
     ✅ Adds Anvil Plugin
     ✅ Removed injectLegacy
     dependency
     Done by Product teams
     2
     

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101. Involving product teams
     1. Step by step guide
     
     2. Tracked the process
     
     3. Capacity of the teams
     
     4. Explained the bene
     fi
     ts
     Explained the bene
     fi
     ts
     

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102. Involving product teams
     Explained the bene
     fi
     ts
     ✅ Height of the SFA
     ✅ Skip Kapt
     The build time of their SFA
     library will be reduced
     :
     

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103. Involving product teams
     Explained the bene
     fi
     ts
     ✅ Height of the SFA
     ✅ Skip Kapt
     The build time of the app
     will be ALSO reduced
     :
     

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104. 😭 ☹ 😶 🙂 🤩
     

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106. core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     core_lib
     injectLegacy
     BaseComponent
     BaseSessionComponent
     feature_lib
     core_lib
     Legacy monoliths
     injectLegacy
     ✅ Removed injectLegacy dependency
     ✅ Add Anvil plugin (if necessary)
     Done by Platform team
     1
     ✅ Adds Anvil Plugin
     ✅ Removed injectLegacy
     dependency
     Done by Product teams
     2
     ✅ Delete injectLegacy
     Done by Platform team
     3
     

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107. Legacy monoliths
     injectLegacy
     

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108. Legacy monoliths
     injectLegacy
     🔪💀
     

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109. Results
     

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110. 20
     The height of the app module
     

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111. 11
     The height of the app module
     20
     

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112. 45% 🎉
     The height of the app module
     

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113. 24 minutes
     Full app build time (./gradlew clean app:assembleDebug)
     

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114. 6 minutes
     Full app build time (./gradlew clean app:assembleDebug)
     24 minutes
     

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115. 75% 🎉
     Full app build time (./gradlew clean app:assembleDebug)
     

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116. Take-aways
     

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117. 👀 Gradle dependency graph
     

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118. 🔁 Iterate
     

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119. 🕵 Discovery
     

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120. 📈 Continuous monitoring
     

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121. 📚 Documentation
     

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122. 💪 Challenge the status quo
     

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123. Thanks ❤
     Antoni Castejón
     @antoni_castejon
     

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