Lift & Shift, Cut Overs, and other Bad Habits

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Lift & Shift, Cut Overs, and other Bad Habits Product Manager [email protected]

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Agenda - Intro - What are Design Patterns? - Rethinking for the Cloud - Strangler - Publisher/Subscriber - Circuit Breaker - Next Steps

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Who am I?

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Who am I?

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Who am I?

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What are Design Patterns?

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7 7 7 A way to express a complex solution to a problem in a simple, repeatable way We do this in many areas - Goldilocks - Catch 22 - Kobayashi Maru What is a Design Pattern?

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8 8 8 What are some familiar ones?

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Types of Design Patterns Creational Structural Behavioral Scope Class Factory Adapter Interpreter Object Abstract Factory Adapter Chain of Responsibility Builder Bridge Command Prototype Composite Iterator Singleton Decorator Mediator Facade Observer Flyweight Strategy Proxy Visitor

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10 10 10 The Old World - Direct access to systems - 3-tier architecture (presentation, app, data) - Simple request/response - Local request/response - Potentially single server - Predictable components & conﬁgurations - Complete control over the stack The New(ish) World - DevOps and Build pipelines - Microservices - Distributed systems - Ephemeral systems - Scalable, unpredictable architecture - Predictable conﬁgurations - Minimal control for developers Why they break down

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Our Approaches

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Lift & Shift: What we Think

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Lift & Shift: Reality

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Lift & Shift: Reality

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Cut Overs: What we Think

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Cut Overs: Reality

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Other Ideas - Hybrid: What we Think

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Other Ideas - Hybrid: Reality

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Rethinking for the Cloud

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20 20 20 - Microservices - Distributed Logging - Federated Identity - Load Balancing - Promises - Service Discovery - Service Mesh - Sidecars - Mock Objects - Work Objects What’s out of bounds this time?

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Disclaimer: These are descriptive, not prescriptive.

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22 22 22 “If you know the problem and know yourself, you need not fear the result of a hundred releases. If you know yourself but not the problem, for every release you will also suffer downtime. If you know neither the problem nor yourself, you will break everything and have no ﬂippin’ clue why.” ~ Sun Tzu Some Wisdom

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The Strangler

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What problem do we have? We have an old system We want to have a new system The old system has to keep working

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What does this pattern do? Old System Facade Old System Old System Old Facade New Old Facade New New System Facade

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When do we use it? The old system has to keep working We want to separate/isolate components Great for testing high risk components Ref: https://martinfowler.com/bliki/StranglerFigApplication.html

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Do you have a single point of entry/control? Now you have to maintain the facade too! Can the facade keep up with the changes? Is the facade a single point of failure? Can both systems handle data jointly? What are the tradeoffs?

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Blue/Green Deployments Highway Bypasses What does it look like in the wild?

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Publisher/ Subscriber

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We have distributed components that need to interact We may not have a list of every listener Not every listener cares about every message What problem do we have?

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What does this pattern do? Ref: https://learn.microsoft.com/en-us/azure/architecture/patterns/publisher-subscriber

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When do we use it? We have distributed, event-driven systems We don’t have control over the endpoints We have varied architectures, languages, etc Our listeners are scaling quickly or are ephemeral

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What are the tradeoffs? Security - there are many ways to screw this up This is a broadcast-only, not bi-directional Messages will be received out of order Messages can be lost or repeated Can you replay messages?

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What does it look like in the wild? Webhooks!* Airports

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Circuit Breaker

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What problem do we have? Things break! Things come back! We have to protect our app and users

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Protects the system but cutting off - or breaking - connectivity to other systems Optionally: Provide a fallback option Optionally: Monitor the underlying system and recover automatically once it’s restored What does this pattern do? Ref: https://martinfowler.com/bliki/CircuitBreaker.html

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Any time we want to isolate a dependency/subsystem AND Our system can be “useful enough” without the subsystem When do we use it?

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Ref: https://aws.amazon.com/blogs/compute/using-the-circuit-breaker-pattern-with-aws-step-functions-and-amazon-dynamodb/ What are the tradeoffs? How do we handle the exceptions? How do we trigger a reset/recovery? How do we test success, failure, and the transition states? Some things should knock our systems ofﬂine

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What does it look like in the wild? Circuit breakers Trafﬁc reports

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Wrap Up

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- Design Patterns - complex ideas in simple repeatable explanations - Rethinking for the Cloud - our constraints have changed - Strangler - replace an old system safely over time - Publisher/Subscriber - communicate between distributed systems - Circuit Breaker - protect your system & recover from failures Recap

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43 43 43 Pulling these together CB old system facade client new system monitoring

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44 44 44 - Microservices - Distributed Logging - Federated Identity - Load Balancing - Promises - Service Discovery - Service Mesh - Sidecars - Mock Objects - Work Objects Other Cloud Design Patterns

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45 45 45 Where can I learn more? - Martin Fowler’s Patterns of Legacy Displacement - Microsoft’s Azure Architecture Center - PHP: Design Patterns on LinkedIn - webhooks.fyi - In progress: DesignPatterns.fyi

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Lift & Shift, Cut Overs, and other Bad Habits Product Manager [email protected]