Splitting a Monolith Using Feature Flags

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Using Feature Flags How to Split a Monolith Joy Ebertz Sr Staff Engineer

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Who am I? https://medium.com/@jkebertz

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Who am I? • At Box • Worked on many aspects of splitting a monolith • Architecture • Authorization service • Service moving functionality • At Split • Work on a feature flagging system • Starting to think through splitting our monolith

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Agenda • What are feature flags? • Why split a monolith? • Challenges of Splitting a Monolith • How can feature flags help?

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What Are Feature Flags?

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Other Terms • Feature Toggle • Feature Flip • Feature Switch • Conditional Feature • Split

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Code Branch Controlled by GUI

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Code Sample if (Treatments.ON .equals(_splitClient.getTreatment(orgId, Splits.MY_FEATURE.name()))) { // Do Something } else { // Do Something Else }

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Code Sample if (Treatments.ON.equals(_splitClient.getTreatment(orgId, Splits.MY_FEATURE.splitName()))) { // Do Something } else { // Do Something Else }

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Main Use-Cases • Releasing features • Production Testing • A/B/C Testing • Custom Packages • Temporary UI Customization

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Main Use-Cases • Releasing features • Production Testing • A/B/C Testing • Custom Packages • Temporary UI Customization

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Releasing Features • Separating Deploy from Release • Canary/Ramped Deployment • Off Switch

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Deploy Release

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User

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Prod User

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Prod User

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Prod Developer

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Prod Developer

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Prod User

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Prod User Split

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Prod User Split OFF OFF

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Prod User Split OFF

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Prod User Split OFF

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Prod Split Product Owner OFF

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Prod Split Product Owner ON

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Prod User Split ON

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Prod User Split ON

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Prod User Split ON

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Prod User Split ON

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Prod Developer

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Prod Developer

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Prod User Split 10%

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Prod User Split 20%

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Why Should We Split a Monolith?

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What do I mean by “Splitting a Monolith?”

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Why Split a Monolith? Code Entanglement

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Controllers Models Smarty Templates

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Controllers Models Smarty Templates Actions!

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Controllers Models Smarty Templates Actions

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Controllers Models Smarty Templates Actions New Actions

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New Actions Controllers Models Smarty Templates Actions New Actions

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Controllers Models Smarty/Brainy Templates Actions New Actions New New Actions Commands Views Services Resolvers Runmode

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Controllers Models Smarty Templates Actions New Actions New New Actions Command s Views Services Resolvers Runmode

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Controllers Models Smarty Templates Actions New Actions New New Actions Command s Views Services Resolvers Runmode

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Controllers Models Smarty Templates Actions New Actions New New Actions Command s Views Services Resolvers Runmode

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Controllers Models Smarty/Brainy Templates Actions New Actions New New Actions Commands Views Services Resolvers Runmode

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Controllers Models Actions New Actions New New Actions Commands Views Services Resolvers Runmode Smarty/Brainy Templates Webapp Controller Webapp DataProvider

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Controllers Models Actions New Actions New New Actions Commands Views Services Resolvers Runmode Smarty/Brainy Templates Webapp Controller Webapp DataProvider

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Unclear Ownership

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Deployment Problems

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Build Test Deploy

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Build Test Deploy

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Build Test Deploy

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Build Test Deploy

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Build Test Deploy

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Build Test Deploy

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Build Test Deploy

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10% 10% 10% Deploy 72% Chance Of Success

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10% 10% 10% Deploy 53% Chance Of Success 10% 10% 10%

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10% 10% 10% Deploy 28% Chance Of Success 10% 10% 10% 10% 10% 10% 10% 10% 10%

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Deploy 1% Chance Of Success

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Deploy

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Deploy

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Deploy

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Deploy

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Challenges of Splitting a Monolith

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Original Code Tangled

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Entirely Separate Talk

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Trying to Replicate Functionality

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Entirely New Infrastructure

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Entirely New Infrastructure

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RISKY

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So, how can we mitigate the risks?

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Using Feature Flags to Split a Monolith

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Minimize Move

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Remove Dead Code

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Why is your code dead? Method no longer referenced Parameter never has certain values Endpoint never called

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log.info(“CODE NOT DEAD UID: 12345”);

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private void logForCleanup(String orgId, String uid) { if (Treatments.ON .equals(_splitClient.getTreatment(orgId, Splits.CLEANUP.name()))) { String message = String.format(“CODE NOT DEAD UID: %s”, uid); log.info(message); } }

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1. Roll out to 1% 2. Remove any lines hit 3. Roll out to 5% 4. Remove any lines hit 5. Roll out to 100% (leave here as long as makes you comfortable) 6. Remove any code that hasn’t been hit

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Requests Monolith logic

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Requests Monolith logic Interface

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Requests Monolith logic New Microservice Interface Interface

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Requests Monolith logic New Microservice Interface Interface

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Requests Monolith logic New Microservice Interface Interface

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Stress Test Your New Systems

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Requests Monolith logic New Microservice Mirrored Traffic

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Requests New Microservice Mirrored Traffic Feature Flag Check Monolith logic

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Requests New Microservice Mirrored Traffic Feature Flag Check Monolith logic

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Requests New Microservice Mirrored Traffic Feature Flag Check Monolith logic

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Requests New Microservice Mirrored Traffic Feature Flag Check Monolith logic

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Verify Parity

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Requests New Microservice Feature Flag Parity Check Monolith logic

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Requests New Microservice Feature Flag Parity Check Monolith logic

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Requests New Microservice Feature Flag Parity Check Monolith logic

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Requests New Microservice Feature Flag Parity Check Monolith logic

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Requests New Microservice Feature Flag Parity Check Monolith logic Log if different

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Requests New Microservice Feature Flag Parity Check Monolith logic Log if different

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Requests New Microservice Feature Flag Parity Check Monolith logic Log if different

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Slowly Roll Over Traffic

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Slowly Roll Over Traffic 1%

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Slowly Roll Over Traffic Free Users

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Slowly Roll Over Traffic Internal Users

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Slowly Roll Over Traffic Test Traffic Only

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Slowly Roll Over Traffic

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• Treatments.OLD • Treatments.NEW • Treatments.BOTH • Treatments.PARITY Default OFF treatment

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Requests New Microservice Monolith logic Treatments.OLD

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Requests New Microservice Monolith logic Treatments.NEW

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Requests New Microservice Mirrored Traffic Monolith logic Treatments.BOTH

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Requests New Microservice Monolith logic Treatments.PARITY Parity Check

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Summary • What are feature flags? • Why split a monolith? • Challenges of Splitting a Monolith • How can feature flags help? • Remove dead code • Load test • Parity check • Gradual roll out/kill switch

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What Are Feature Flags? Joy Ebertz @jkebertz Thank You!