Microservices, Bounded Contexts, and Everything in Between

Microservices, Bounded Contexts, and Everything in Between

DDD eXchange 2018

B90ab53ba7cf16ed1a4bb679cc6751d7?s=128

Vladik Khononov

April 26, 2018
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  1. Microservices Bounded Contexts And Everything in Between

  2. @vladikk vladikk.com

  3. ”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
  4. “MICROSERVICES FTW!!!!!!!!1” Me @ Internovus

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

  6. ”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
  7. None
  8. None
  9. Decomposition Strategies Bounded Contexts, Business Domains, 
 Business En66es Design

    Heuristics Microservices Wrap-up Example Business Domain 1 2 3 4 5
  10. Your Product Marketing
 Strategy Creatives Campaigns Sales
 Agents Optimization Profits

  11. Decomposi9on Strategies Bounded Contexts Subdomains Business Entities and Processes

  12. Bounded Contexts

  13. None
  14. Domain Expert Software Developer

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

  16. Campaigns Sales
 Agents Your Product Marketing
 Strategy Creatives Optimization Profits

  17. Sales Agent Campaign Manager ??? !!! LEAD?

  18. Conflicting models Different contexts Dividing the language/model Bounded Context

  19. Marke9ng Sales Lead Lead Funnel Campaign Placement Landing Page Agency

    Insertion Order Message Campaign Proposition Desk Conversion Contact CDR Bounded Contexts
  20. Marke9ng Service Sales Service Decomposi9on Strategy #1: Bounded Contexts

  21. Marke9ng Sales Commissions Desks Sales
 Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ads Optimization Identity & Access
  22. Subdomains

  23. 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
  24. Decomposi9on Strategy #2: Subdomains Campaign Management Service Content Catalog Service

    Desks Management Service CRM Service Users Service Billing Service
  25. Business En99es and Processes

  26. Marke9ng Creative Catalog Contracts Billing Campaign Management Identity & Access

    Optimization Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone Asset Publisher Target Market
  27. Decomposi9on Strategy #3: En99es Website Asset Target Market Broker Distribu6on

    Customer
  28. Decomposi9on Strategies Bounded Contexts Subdomains Business Entities and Processes

  29. SHOW ME THE MICROSERVICES!

  30. Bounded Contexts == Microservices ?

  31. Sales Agent Campaign Manager ??? !!! LEAD?

  32. Marke9ng Sales Lead Lead Funnel Campaign Placement Landing Page Agency

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

    Insertion Order Message Campaign Proposition Desk Conversion Contact CDR
  34. Marke9ng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

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

    Billing Campaign Management Identity & Access Optimization Identity & Access Lead Lead
  36. Marke9ng Creative Catalog Campaign Management Optimization Lead Sales Commissions Optimization

    CRM Lead Desks Telephony Support Contracts Billing Identity & Access
  37. None
  38. Bounded Context Consistency boundary of the language / model Define

    the biggest valid monoliths Required decomposition boundary
  39. Bounded Contexts == Microservices? No

  40. 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?
  41. Microservices

  42. 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
  43. “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
  44. Service Interface “Any mechanism for getting data in or out

    of the service” - Randy Shoup
  45. Service Interface Asynchronous: • Producing events • Consuming events Synchronous:

    • Request / Réponse • Bulk ETL
  46. Service Interface “Any mechanism for getting data in or out

    of the service” - Randy Shoup
  47. Service Interface

  48. Services ➜ Microservice

  49. A microservice is a service with a micro interface

  50. Microservice = Microinterface Reducing coupling between services Limits reasons for

    change Easier to understand Better fault isolation More autonomy between services
  51. Microservice & Databases Microservices should own its database No external

    access Access through Microservice’s API only Database = infinite interface!
  52. But!

  53. 1 Method = Perfect Microservice !!??

  54. None
  55. None
  56. None
  57. None
  58. STAFF ONLY STAFF ONLY

  59. 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.
  60. Monolith Microservices Distributed
 Monolith Cost of Change

  61. Big Ball Of Mud Bounded Contexts Microservices Distributed Big Ball

    Of Mud Avg. Service Size
  62. Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone

    Asset Publisher Target Market Campaign Website Placement Funnel Subdomains? En99es?
  63. None
  64. ”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
  65. ”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
  66. 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
  67. Services + Good Engineering = Microservices

  68. 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
  69. 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
  70. 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.
  71. 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?
  72. Design Heuris9cs

  73. Heuris9c #1: Decompose to Bounded Contexts Do not implement conflicting

    models in the same service. Always decompose to Bounded Contexts.
  74. Heuris9c #2: Don’t ”First Law of Distributed Object Design: 


    “Don’t distribute your objects” Mar9n Fowler
  75. Heuris9c #2: Don’t Benefits Addi6onal
 Complexity

  76. Heuris9c #2: Don’t Benefits Addi6onal Complexity

  77. Core Supporting Generic

  78. Generic Subdomains No competitive advantage Everybody is implementing in the

    same way Complex business logic
  79. Marke9ng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  80. Heuris9c #3: Buy/Adopt Generic Subdomains Your System 3rd party product

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

    An6-Corrup6on Layer
  82. Core Subdomains Inventing something new Optimizing existing paractices Competitive advantage

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

    Complex business logic Change often
  84. Heuris9c #4: Core Subdomains - Don’t Rush Adhere to subdomain’s

    boundaries. Decompose further only when you acquire domain knowledge.
  85. Suppor9ng Subdomains No competitive advantage Support the Core Subdomains Can’t

    be bought / adopted Simple business logic
  86. Marke9ng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  87. Suppor9ng Subdomains No competitive advantage Support the Core Subdomains Can’t

    be bought / adopted Simple business logic
  88. Heuris9c #5: Suppor9ng Subdomains - Early Can be decomposed beyond

    the subdomain’s boundaries.
  89. Core Supporting Generic

  90. Heuris9c #6: Evaluate Consistency Requirements Method A Method B

  91. Heuris9c #6: Evaluate Consistency Requirements Concurrency control? - Same service

    Method A Method B 
 Service A
  92. Heuris9c #6: Evaluate Consistency Requirements Read last write? - Two

    services, synchronous communication 
 Service A Method A 
 Service B Method B Sync call
  93. Heuris9c #6: Evaluate Consistency Requirements Eventual consistency? - Two services,

    asynchronous communication 
 Service A Method A 
 Service B Method B Asynchronous Communication
  94. Heuris9c #6: Evaluate Consistency Requirements Concurrency control? - Same service

    Read last write? - Two services, sync communication Eventual consistency? - Two services, async communication
  95. 
 Service A Method A 
 Service B Method B

    Asynchronous Communication
  96. 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) }
  97. Service EmailChanged PhoneNumberChanged AddressChanged ContactDetailsChanged Private event types (Implementation details)

    } Public event type (Public interface) } Heuris9c #7: Public / Private Events
  98. Heuris9c #7: Public / Private Events Events?

  99. Heuris9c #7: Public / Private Events Events? Domain Events State

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

    Change
 Events Private Public
  101. Heuris9c #8: Make Events Explicit Eliminate ambiguity

  102. Heuris9c #8: Make Events Explicit Service AgentAssignedToLead

  103. Heuris9c #8: Make Events Explicit Service AgentAssignedToLead AgentAssignedToLead AgentAssignedToLead

  104. Heuris9c #8: Make Events Explicit Service AgentAssignedToLead AgentUnassigned AgentAssignedToLead

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

  106. Same reasons for change? Same rate of change? Can be

    decoupled? Should be the same service? Heuris9c #9: Evaluate Reasons for Change
  107. Heuris9c #10: Evaluate Services’ “Doors”

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

  109. Summary

  110. 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
  111. 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
  112. 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”
  113. Big Ball Of Mud Bounded Contexts Microservices Distributed Big Ball

    Of Mud Avg. Service Size
  114. 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
  115. THANK YOU! @vladikk vladikk.com

  116. QUESTIONS? @vladikk vladikk.com

  117. THANK YOU! @vladikk vladikk.com