Tackling Android at Scale

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android.scale() @fabiocarballo

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“Building a bank the world loves to use.

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Hypergrowth mode

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2014

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2014 5 Number of Android devs

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2016 5 Number of Android devs

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2016 5 Number of Android devs

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2017 5 Number of Android devs

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5 2018 15 Number of Android devs

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27 15 5 Now Number of Android devs

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500% 1.5 years

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Technical Readiness Scale Recruiting Onboarding Automation Releases Team Culture

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How do we approach code?

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Broken Windows

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What to consider defining your architecture?

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What to consider defining your architecture? -Reduce number of discussions -Embrace evolution -Favour testability -Protects from making mistakes

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Architecture

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Activity Reactive Dependency Injection Layered Architecture core:

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Reactive

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Receive 10 € into Main Account Reactive

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S1 S1 S2 S3 S1 spaces reactive store Receive 10 € into Main Account spaces microservice GET /spaces Reactive Space Details View Model

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spaces reactive store spaces microservice GET /spaces Reactive Receive 10 € into Main Account Space Details View Model

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S1 S2 S3 Spaces Dashboard View Model Space Details View Model spaces reactive store spaces microservice GET /spaces Reactive Receive 10 € into Main Account

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S1 S2 S3 S2 S3 S1 S2 S3 S1 S2 S3 Space Details View Model spaces reactive store spaces microservice GET /spaces Reactive Receive 10 € into Main Account Spaces Dashboard View Model

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Feature Layered Architecture

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Domain Feature Presentation Data

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Domain Presentation Data Dependency Injection

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Domain Presentation Data Dependency Injection

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Domain Presentation Data Dependency Injection Dagger Glue

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Be ruthless about it Defining your tech stack

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-Which problem is it solving? Defining your tech stack

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-Which problem is it solving? -What is the impact? Defining your tech stack

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-Which problem is it solving? -What is the impact? -Is it actively maintained? Defining your tech stack

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-Which problem is it solving? -What is the impact? -Is it actively maintained? 2.0.1 2.0.2 2.1.0 2.2.0 2.3.0 2.4.0 2.5.0 Retroﬁt Version along 2.5 years Defining your tech stack

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Wrapping 3rd parties behind an interface is actually good.

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Wrapping 3rd parties behind an interface is actually good.

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app Camera Lib 1 - Keeping two Camera libs in the app Wrapping 3rd parties behind an interface is actually good.

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app Camera Lib 1 - Keeping two Camera libs in the app Wrapping 3rd parties behind an interface is actually good.

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app Camera Interface Camera Lib 1 - Keeping two Camera libs in the app Wrapping 3rd parties behind an interface is actually good.

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- Keeping two Camera libs in the app app Camera Interface Camera Lib 2 Camera Lib 1 Wrapping 3rd parties behind an interface is actually good.

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app Camera Interface Camera Lib 2 Camera Lib 1 Compression issues! camera_lib: “camera_lib_2” camera_lib: “camera_lib_2” “camera_lib_1”

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app Camera Interface Camera Lib 2 Camera Lib 1 Compression issues! camera_lib: “camera_lib_2” “camera_lib_1”

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Workflow Fabio Lucia

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Fábio Lucia Workflow

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Fábio Lucia Mustafa Omkar Ilke Sergio

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Fábio Lucia Streams of work for 20+ persons a.k.a. Possibly many merge conflicts

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Fábio Lucia Branch out and branch in small chunks Feature Flags

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Commit Messages new transaction details NewTransactionsList WIP Linked- Authorising transactions dialog

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android-machete git:(DES-156-discreet) android-machete git:(develop) git add . git checkout -b DES-156-discreet Switched to a new branch `DES-156-discreet` android-machete git:(DES-156-discreet) git commit -m “add discreet section to glossary” | JIRA ticket 'DES-156' prepended to commit message [DES-156-discreet 6219e9cbd4] DES-156 add discreet section to glossary

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Modularisation for independence

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app

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Oct 14 Jan 2016 Jan 2017 Jan 2018

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app

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User app Login

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app User Login Security

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app Certification Security User Login Credit

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app Credit Security User Login Certification

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app Credit Security User Login Certification

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app Certification Security User Login Credit Hidden coupling

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app User Login Certification Security Credit Hidden coupling

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app User Login Certification Security Credit

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app User Login Certification Security Credit

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Transactions

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:transactions domain :transactions presentation :transactions data

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:transactions domain :transactions presentation :app :transactions data

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:spaces data :spaces domain :spaces presentation :moneyBeam data :moneyBeam domain :moneyBeam presentation :transactions presentation :app :transactions domain :transactions data

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Jan 2019 100 modules Oct 14 Jan 2016 Jan 2017 Jan 2018

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:transactions data :transactions domain :transactions presentation :app :spaces data :spaces domain :spaces presentation :moneyBeam data :moneyBeam domain :moneyBeam presentation

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:transactions :app :spaces :moneyBeam

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:transactions :app :spaces :moneyBeam moneyBeam microservice transactions microservice spaces microservice

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:transactions :app :spaces :moneyBeam Backend for Frontend service moneyBeam microservice transactions microservice spaces microservice

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100 modules Jan 2019 Oct 14 Jan 2016 Jan 2017 Jan 2018

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What about … build times? They are interesting

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Jan 2019 Oct 14 Jan 2016 Jan 2017 Jan 2018 7m 5m 3m 1.5m Clean Build Times

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40% of reduction in build times Jan 2019 Oct 14 Jan 2016 Jan 2017 Jan 2018 7m 5m 3m 1.5m Clean Build Times

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Feature Launcher Apps

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Credit

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Credit N26 App

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N26 App Credit Spaces Overdraft Premium Moneybeam Transactions

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N26 App Credit Spaces Overdraft Premium MoneyBeam Transactions 1-5mins build time

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Launcher app Credit N26 App Spaces Overdraft Premium MoneyBeam Transactions 1-5mins build time

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Go bottom-top, not top-bottom

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:app

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AppComponent NetworkModule ApplicationModule SpacesComponent SpacesModule UserComponent User Module Session Module Credit Component CreditModule :app

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:spaces :credit SpacesComponent SpacesModule Credit Component CreditModule AppComponent NetworkModule ApplicationModule UserComponent User Module Session Module :app

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:spaces :credit SpacesComponent SpacesModule Credit Component CreditModule AppComponent NetworkModule ApplicationModule UserComponent User Module Session Module :app Where is App/User component??????

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:spaces :credit :base BaseComponent NetworkModule ApplicationModule Session Module SpacesComponent SpacesModule Credit Component CreditModule :app

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Why modularize for scale? Independent teams

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Refactor with more safety Independent teams Why modularize for scale?

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Independent teams Refactor with more safety Creativity and Innovation Why modularize for scale?

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Testing to release with trust

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Oct 14 Jan 2016 Jan 2017

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Unit Tests Oct 14 Jan 2016 Jan 2017 Easy Safe Refactoring Let you sleep

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Unit Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests Easy Safe Refactoring Let you sleep

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Easy Safe Refactoring Let you sleep Unit Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests

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Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests Unit Tests

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Unit Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests

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Unit Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests

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Unit Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests

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Unit Tests Functional UI Tests 400 UI Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests

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Automated Regression 10% 50% Functional UI Tests 400 UI Tests Unit Tests Oct 14 Jan 2016 Jan 2017 Jan 2018 Jan 2019 8000 Unit tests

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UI Testing Pipeline Slow Most diﬀicult to fix

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ui-pipeline.sh

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SpacesViewModel + spaceName.text = “Space” - spaceName.text = space.name ui-pipeline.sh

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:app :spaces :c :b :a ui-pipeline.sh SpacesViewModel + spaceName.text = “Space” - spaceName.text = space.name

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:spaces ./run-instrumentation spaces :app :spaces :c :b :a ui-pipeline.sh SpacesViewModel + spaceName.text = “Space” - spaceName.text = space.name

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30+ minutes UI Testing Pipeline

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3 min (worst case run) UI Testing Pipeline

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Build a Design System and bring consistency alongside

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80 Designers & Engineers 15 Designers & Engineers

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That one “divider grey” Yeah it should be the grey we used in that other screen :) Is this the right grey for the divider? I thought it was this one? Hmm, I was using this to be honest

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System Glossary

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listOf(

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SectionHeader("Transactions"), listOf(

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SectionHeader("Transactions"), listOf( SubSectionHeader(“Today"),

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TransactionContainer( "From Main Account", " to Home", Money(BigDecimal(5), Euro)), TransactionContainer( "From Main Account", "Last one ... ", Money(BigDecimal(4.50), Euro)), TransactionContainer( "From Main Account", "Just one more ", Money(BigDecimal(5), Euro)), TransactionContainer( "From Main Account", "Money for drinks!", Money(BigDecimal(5), Euro)))) SectionHeader("Transactions"), listOf( SubSectionHeader(“Today"),

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Consistency Speed

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Discreet Mode

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Discreet Mode

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Discreet Mode In a company of 1000+ people, 2 persons were able to develop and drive the launch of this feature QA Design Marketing Product Bank Security

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QA Design Marketing Product Bank Security Discreet Mode In a company of 1000+ people, 2 persons were able to develop and drive the launch of this feature

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Discreet Mode In a company of 1000+ people, 2 persons were able to develop and drive the launch of this feature QA Design Marketing Product Bank Security

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Questions? n26.com/careers Berlin Barcelona New York Vienna Follow me: @fabiocarballo