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A Question of Size Stefan Tilkov, [email protected], @stilkov Java Forum Nord 2017

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Reviewing architectures

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Generic Architecture Review Results Building features takes too long Technical debt is well-known and not addressed Deployment is way too complicated and slow Replacement would be way too expensive Scalability has reached its limit Architectural quality has degraded “-ility” problems abound

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So let’s start with this …

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… and cut it apart: Voilà, Microservices!

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“Microservices” are building blocks of an architectural style that uses deployment boundaries as a first-class software architecture principle

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How big shall each individual service be?

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Just make things the right size

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High Cohesion Loose Coupling

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Vocabulary http://vanderburg.org/blog/Software/Development/cohesion.rdoc inherent: existing in something as a permanent, essential, or characteristic attribute adhesive: able to stick fast to a surface or object; sticky: cohesive: characterized by or causing cohesion cohesion: the action or fact of forming a united whole;
 in physics: the sticking together of particles of the same substance

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Separate separate things Join things that belong together

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Building blocks procedures functions libraries modules units objects classes images dynamic libraries shared objects components services microservices VMs containers lambdas

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Commonalities dependencies boundary interface environment implementation

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Information Hiding “[I]t is almost always incorrect to begin the decomposition of a system into modules on the basis of a flowchart. We propose instead that one begins with a list of difficult design decisions or design decisions which are likely to change. Each module is then designed to hide such a decision from the others.” David L. Parnas, 1971 http://www.cs.umd.edu/class/spring2003/cmsc838p/Design/criteria.pdf

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Single Responsibility Principle “A class [or module] should only have one reason to change. […] The SRP is one of the simplest of the principles, and one of the hardest to get right. Finding and separating those responsibilities from one another is much of what software design is really about.” “There is a corrolary here. An axis of change is only an axis of change if the changes actually occur.” Robert C. Martin, 1995/2003 http://www.butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

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Indicators of strong cohesion simple to understand simple to explain one reason to change one stakeholder difficult to split (re-)used as a whole

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Indicators of weak cohesion hard to understand difficult to explain many reasons to change multiple stakeholders obviously divisible partially re-used

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Forces for separation Different environments (scale, performance, security, …) Parallel/isolated runtime Crosscutting concerns Frequency of change Parallel/isolated development Need for reuse Technical dependencies Domain dependencies Implementation Weight

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Multiple Dimensions Different Priorities

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System Layered system Logic Data UI Module Module Module

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System System System System of systems Logic Data UI Logic Data UI Logic Data UI

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Let’s talk about Microservices

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Microservices – Common Traits > Independent deployment > Focused on “one thing” > Autonomous operation > Isolated development > Localized decisions

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Benefits 1. Isolation 2. Autonomy 3. Indidual Scalability 4. Resilience 5. Speed 6. Experimentation 7. Rapid Feedback 8. Flexibility 9. Replaceability 10. Ecosystem

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Example: Pricing Engine > Default product prices > General discounts > Customer-specific discounts > Campaign-related rebates Event Bus/Infrastructure →FaaS

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FaaS – Function as a Service > As small as possible > A few hundred lines of code or less > Triggered by events > Communicating asynchronously Characteristics: As seen on: > Any recent Fred George talk > Serverless Architecture(*) > AWS Lambda (*) https://leanpub.com/serverless

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FaaS – Function as a Service > Close collaboration – common goal > Shared strong infrastructure dependency > Common interfaces, multiple invocations > Close similarity to actor-based environments > Well suited to decomposable/“fuzzy” business problems Consequences:

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Example: Product Detail Page > Core product data > Prose description > Images > Reviews > Related content Orchestration →μSOA

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μSOA – Microservice-oriented Architecture > Small, self-hosted > Communicating synchronously > Cascaded/streaming > Containerized Characteristics: As seen on: > Netflix > Twitter > Gilt

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μSOA – Microservice-oriented Architecture > Close collaboration – common goal > Need for resilience/stability patterns for invocations > Often combined with parallel/streaming approach > Well suited to environments with extreme scalability requirements Consequences:

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Antipattern: Decoupling Illusion Stakeholder Stakeholder Stakeholder Platform Person

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Example: Logistics Application > Order management > Shipping > Route planning > Invoicing Frontend →DDDD Event Bus/Infrastructure

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DDDD – Distributed Domain-driven Design > Small, self-hosted > Bounded contexts > Redundant data/CQRS > Business events > Containerized Characteristics: As seen on: > (undisclosed)

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DDDD – Distributed Domain-driven Design > Loose coupling between context > Acknowledges separate evolution of contexts > Asynchronicity increases stability > Well-suited for to support parallel development Consequences:

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That UI thing? Easy!

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Assumption

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Reality

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Example: E-Commerce Site > Register & maintain account > Browse catalog > See product details > Checkout > Track status →SCS

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SCS – Self-contained Systems > Self-contained, autonomous > Including UI + DB > Possibly composed of smaller microservices Characteristics: As seen on: > Amazon > Groupon > Otto.de > https://scs-architecture.org

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SCS – Self-contained Systems > Larger, independent systems, Including data + UI (if present) > Able to autonomously serve requests > Light-weight integration, ideally via front-end > No extra infrastructure needed > Well suited if goal is decoupling of development teams Consequences:

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Web UI Integration: Links System 1 System 2

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Web UI Integration: Redirection System 1 System 2

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Web UI Integration: Transclusion System 1 System 2

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Building Block 0..1 *

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So what?

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Summary & Recommendations

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1.
 Explicitly design system boundaries

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2.
 Start front-to-back instead of
 top-down or bottom-up

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3.
 Modularize systems using the appropriate approach, including monoliths

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Stefan Tilkov
 [email protected]
 Phone: +49 170 471 2625 innoQ Deutschland GmbH Krischerstr. 100 40789 Monheim am Rhein Germany Phone: +49 2173 3366-0 innoQ Schweiz GmbH Gewerbestr. 11 CH-6330 Cham Switzerland Phone: +41 41 743 0116 www.innoq.com Ohlauer Straße 43 10999 Berlin Germany Phone: +49 2173 3366-0 Ludwigstr. 180E 63067 Offenbach Germany Phone: +49 2173 3366-0 Kreuzstraße 16
 80331 München Germany Phone: +49 2173 3366-0 @stilkov That’s all I have. thanks for listening!

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About Stefan Tilkov > CEO/Co-founder & principal consultant
 at innoQ > Focus on architecture, REST, Web > Messing with technology since 1993 > [email protected], @stilkov

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About innoQ > Offices in Monheim (near Cologne), Berlin, Offenbach, Munich, Zurich > ~125 employees > Core competencies: software architecture consulting and software development > Privately owned, vendor-independent > Clients in finance, telecommunications, logistics, e- commerce; Fortune 500, SMBs, startups www.innoq.com

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Image Credit Alice Popkorn, https://flic.kr/p/5NsmsK hairchaser, https://flic.kr/p/aqNWyV