Microservices, Bounded Contexts, and Everything in Between

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Microservices Bounded Contexts And Everything in Between

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@vladikk vladikk.com

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”95% of the words are spent extolling the benefits of “modularity” and that little, if anything, is said about how to achieve it” Glenford J. Myers Composite / Structured Design, 1974

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“MICROSERVICES FTW!!!!!!!!1” Me @ Internovus

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“MICROSERVICES FTW!!!!!!!!1” Me @ Internovus

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”95% of the words are spent extolling the benefits of “modularity” and that little, if anything, is said about how to achieve it” Glenford J. Myers Composite / Structured Design, 1974

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Decomposition Strategies Bounded Contexts, Business Domains,   Business En66es Design Heuristics Microservices Wrap-up Example Business Domain 1 2 3 4 5

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Your Product Marketing  Strategy Creatives Campaigns Sales  Agents Optimization Profits

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Decomposi9on Strategies Bounded Contexts Subdomains Business Entities and Processes

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Bounded Contexts

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Domain Expert Software Developer

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Business Domain Expert Software Developer ??? !!! Ubiquitous Language

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Campaigns Sales  Agents Your Product Marketing  Strategy Creatives Optimization Profits

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Sales Agent Campaign Manager ??? !!! LEAD?

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Conflicting models Diﬀerent contexts Dividing the language/model Bounded Context

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Marke9ng Sales Lead Lead Funnel Campaign Placement Landing Page Agency Insertion Order Message Campaign Proposition Desk Conversion Contact CDR Bounded Contexts

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Marke9ng Service Sales Service Decomposi9on Strategy #1: Bounded Contexts

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Marke9ng Sales Commissions Desks Sales  Optimization CRM Telephony Creative Catalog Contracts Billing Campaign Management Identity & Access Ads Optimization Identity & Access

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Subdomains

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Business Domain: Customer Acquisi6on Bounded Context: Marke6ng Bounded Context: Sales Subdomain: Crea6ve Catalog Subdomain: Campaigns Mngmt Subdomain: Ads Op6miza6on Subdomain: Contracts Mngmt Subdomain: CRM Subdomain: Sales Op6miza6on Subdomain: Commissions Subdomain: Desks Mngmt

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Decomposi9on Strategy #2: Subdomains Campaign Management Service Content Catalog Service Desks Management Service CRM Service Users Service Billing Service

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Business En99es and Processes

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Marke9ng Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone Asset Publisher Target Market

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Decomposi9on Strategy #3: En99es Website Asset Target Market Broker Distribu6on Customer

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Decomposi9on Strategies Bounded Contexts Subdomains Business Entities and Processes

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SHOW ME THE MICROSERVICES!

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Bounded Contexts == Microservices ?

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Sales Agent Campaign Manager ??? !!! LEAD?

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Marke9ng Sales Lead Lead Funnel Campaign Placement Landing Page Agency Insertion Order Message Campaign Proposition Desk Conversion Contact CDR

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Marke9ng Sales Lead Lead Funnel Campaign Placement Landing Page Agency Insertion Order Message Campaign Proposition Desk Conversion Contact CDR

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Marke9ng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Identity & Access Lead Lead

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Marke9ng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Identity & Access Lead Lead

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Marke9ng Creative Catalog Campaign Management Optimization Lead Sales Commissions Optimization CRM Lead Desks Telephony Support Contracts Billing Identity & Access

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Bounded Context Consistency boundary of the language / model Define the biggest valid monoliths Required decomposition boundary

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Bounded Contexts == Microservices? No

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Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone Asset Publisher Target Market Campaign Website Placement Funnel Marke9ng Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Bounded Contexts? No Subdomains? En99es?

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Microservices

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Service “A service is a unit of functionality exposed to the world” - Juval Lowy “A mechanism to enable access to one or more capabilities, where the access is provided using a prescribed interface” - OASIS

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“A service is a unit of functionality exposed to the world” - Juval Lowy “A mechanism to enable access to one or more capabilities, where the access is provided using a prescribed interface” - OASIS Service

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Service Interface “Any mechanism for getting data in or out of the service” - Randy Shoup

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Service Interface Asynchronous: • Producing events • Consuming events Synchronous: • Request / Réponse • Bulk ETL

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Service Interface “Any mechanism for getting data in or out of the service” - Randy Shoup

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Service Interface

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Services ➜ Microservice

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A microservice is a service with a micro interface

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Microservice = Microinterface Reducing coupling between services Limits reasons for change Easier to understand Better fault isolation More autonomy between services

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Microservice & Databases Microservices should own its database No external access Access through Microservice’s API only Database = infinite interface!

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But!

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1 Method = Perfect Microservice !!??

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STAFF ONLY STAFF ONLY

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The threshold upon which a system can be decomposed into microservices is defined by the use cases of the system that the microservices are a part of.

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Monolith Microservices Distributed  Monolith Cost of Change

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Big Ball Of Mud Bounded Contexts Microservices Distributed Big Ball Of Mud Avg. Service Size

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Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone Asset Publisher Target Market Campaign Website Placement Funnel Subdomains? En99es?

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”Global complexity … the complexity of the overall structure of a program or system. I.e., the degree of association or interdependence among the major pieces of a program” Glenford J. Myers Composite / Structured Design, 1974

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When you design a system…, then if the features can be broken into … loosely bound groups of rela>vely closely bound features, then that division is a good thing to be made a part of the design. This is just good engineering. Tim Berners-Lee Principles of design, 1998

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Services + Good Engineering = Microservices

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Its is not only necessary to make sure your own system is designed to be made of modular parts. It is also necessary to realize that your own system … should always be designed to be a part of another larger system. Tim Berners-Lee Principles of design, 1998

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A major part of this paper will be concerned with the ques>on of how good modularity can be achieved, that is, how modules can be chosen so as to minimize the connec5ons between them. Barbara Liskov A design methodology for reliable soIware systems, 1972

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A microservice is a service with a micro interface. The threshold upon which a system can be decomposed into microservices is defined by the use cases of the system that the microservices are a part of.

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A microservice is a service with a micro interface. The threshold upon which the system can be decomposed is defined by the use cases of the system that the microservices are a part of. …how to evaluate?

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Design Heuris9cs

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Heuris9c #1: Decompose to Bounded Contexts Do not implement conflicting models in the same service. Always decompose to Bounded Contexts.

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Heuris9c #2: Don’t ”First Law of Distributed Object Design:   “Don’t distribute your objects” Mar9n Fowler

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Heuris9c #2: Don’t Beneﬁts Addi6onal  Complexity

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Heuris9c #2: Don’t Beneﬁts Addi6onal Complexity

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Core Supporting Generic

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Generic Subdomains No competitive advantage Everybody is implementing in the same way Complex business logic

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Marke9ng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Identity & Access Generic

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Heuris9c #3: Buy/Adopt Generic Subdomains Your System 3rd party product

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Heuris9c #3: Buy/Adopt Generic Subdomains Your System 3rd party product An6-Corrup6on Layer

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Core Subdomains Inventing something new Optimizing existing paractices Competitive advantage Complex business logic Change often

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Core Subdomains Inventing something new Optimizing existing paractices Competitive advantage Complex business logic Change often

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Heuris9c #4: Core Subdomains - Don’t Rush Adhere to subdomain’s boundaries. Decompose further only when you acquire domain knowledge.

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Suppor9ng Subdomains No competitive advantage Support the Core Subdomains Can’t be bought / adopted Simple business logic

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Marke9ng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting

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Suppor9ng Subdomains No competitive advantage Support the Core Subdomains Can’t be bought / adopted Simple business logic

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Heuris9c #5: Suppor9ng Subdomains - Early Can be decomposed beyond the subdomain’s boundaries.

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Core Supporting Generic

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Heuris9c #6: Evaluate Consistency Requirements Method A Method B

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Heuris9c #6: Evaluate Consistency Requirements Concurrency control? - Same service Method A Method B   Service A

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Heuris9c #6: Evaluate Consistency Requirements Read last write? - Two services, synchronous communication   Service A Method A   Service B Method B Sync call

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Heuris9c #6: Evaluate Consistency Requirements Eventual consistency? - Two services, asynchronous communication   Service A Method A   Service B Method B Asynchronous Communication

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Heuris9c #6: Evaluate Consistency Requirements Concurrency control? - Same service Read last write? - Two services, sync communication Eventual consistency? - Two services, async communication

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  Service A Method A   Service B Method B Asynchronous Communication

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Heuris9c #7: Public / Private Events Service Event Type 1 Event Type 2 Event Type 3 Event Type 4 Event Type 5 Event Type 6 Event Type 1000 … Private event types (Implementation details) }Public event types (Public interface) }

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Service EmailChanged PhoneNumberChanged AddressChanged ContactDetailsChanged Private event types (Implementation details) } Public event type (Public interface) } Heuris9c #7: Public / Private Events

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Heuris9c #7: Public / Private Events Events?

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Heuris9c #7: Public / Private Events Events? Domain Events State Change  Events

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Heuris9c #7: Public / Private Events Events? Domain Events State Change  Events Private Public

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Heuris9c #8: Make Events Explicit Eliminate ambiguity

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Heuris9c #8: Make Events Explicit Service AgentAssignedToLead

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Heuris9c #8: Make Events Explicit Service AgentAssignedToLead AgentAssignedToLead AgentAssignedToLead

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Heuris9c #8: Make Events Explicit Service AgentAssignedToLead AgentUnassigned AgentAssignedToLead

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Heuris9c #9: Evaluate Reasons for Change Service A Service B

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Same reasons for change? Same rate of change? Can be decoupled? Should be the same service? Heuris9c #9: Evaluate Reasons for Change

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Heuris9c #10: Evaluate Services’ “Doors”

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Heuris9c #10: Evaluate Services’ “Doors” STAFF ONLY STAFF ONLY

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Summary

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1. A service is a unit of func6onality exposed to the world through its public interface. 2. A microservice is a service with micro interface 3. The “micro-interface” is rela6ve to the use cases of the system that the service is a part of

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Heuris6c #1: Always decompose to Bounded Contexts Heuris6c #2: Don’t go further, unless you have to Heuris6c #3: Buy/adopt generic subdomains Heuris6c #4: Core Subdomains - don’t rush Heuris6c #5: Suppor6ng Subdomains can be decomposed early

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Heuris6c #6: Evaluate Consistency Requirements Heuris6c #7: Private / Public Events Heuris6c #8: Explicitly Deﬁne Events Heuris6c #9: Evaluate Reasons for Change Heuris6c #10: Evaluate Services’ “Doors”

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Big Ball Of Mud Bounded Contexts Microservices Distributed Big Ball Of Mud Avg. Service Size

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Bibliography 1. A Design Methodology for Reliable Soeware Systems, Barbara Liskov 2. Composite/Structured Design, Glenford Myers 3. Domain-Driven Design: Tackling Complexity in the Heart of Soeware, Eric Evans 4. Emerging Boundaries, Mathias Veraes 5. Implemen6ng Domain-Driven Design, Vaughn Vernon 6. Enterprise Integra6on Paherns, Gregory Hohpe, at al 7. Long Sad Story of Microservices, Greg Young 8. Managing Data in Microservices, Randy Shoup 9. Microservices, At Last Some Boundaries, Eric Evans 10. On the Criteria to be Used in Decomposing Systems Into Modules, David Parnas 11. Paherns of Enterprise Applica6on Architecture, Mar6n Fowler, at al 12. Principles of Design, Tim Berners-Lee 13. Programming WCF Services, Juval Lowy 14. What Every Programmer Should Know About Object Oriented Design, Melir Page-Jones