Bounded Contexts, Microservices, and Everything In Between

Bounded Contexts, Microservices, and Everything In Between

“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, 1978. This quote is 40 years old. Today, 4 decades later, nothing has changed except terminology. Time to fix this.

I want to talk about the various strategies of decomposing systems into modular components. We will learn what exactly Bounded Contexts and Microservices are. See how and why they differ. Analyze what happens between services - how data flows, and how this flow can be optimized. Ultimately, we will explore different decomposition strategies and heuristics for designing modular systems. Systems that aren’t driven by ever-changing fads, but by your business needs.

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Vladik Khononov

October 18, 2018
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  1. 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
  2. 6.
  3. 7.

    ”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. 8.
  5. 9.
  6. 15.
  7. 21.

    MarkeCng Sales Lead Lead Funnel Campaign Placement Landing Page Agency

    Insertion Order Message Campaign Proposition Desk Conversion Contact CDR Bounded Contexts
  8. 23.
  9. 26.

    MarkeCng Sales Commissions Desks Sales
 Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ads Optimization Identity & Access
  10. 28.

    Business Domain: Customer Acquisi/on Bounded Context: Marke/ng Bounded Context: Sales

    Subdomain: Crea/ve Catalog Subdomain: Campaigns Mngmt Subdomain: Ads Op/miza/on Subdomain: Contracts Mngmt Subdomain: CRM Subdomain: Sales Op/miza/on Subdomain: Commissions Subdomain: Desks Mngmt
  11. 29.

    DecomposiCon Strategy #2: Subomains Campaign Management Service Content Catalog Service

    Desks Management Service CRM Service Users Service Billing Service
  12. 32.

    MarkeCng Creative Catalog Contracts Billing Campaign Management Identity & Access

    Optimization Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone Asset Publisher Target Market
  13. 38.

    MarkeCng Sales Lead Lead Funnel Campaign Placement Landing Page Agency

    Insertion Order Message Campaign Proposition Desk Conversion Contact CDR
  14. 39.

    MarkeCng Sales Lead Lead Funnel Campaign Placement Landing Page Agency

    Insertion Order Message Campaign Proposition Desk Conversion Contact CDR
  15. 40.

    MarkeCng Sales Lead Lead Funnel Campaign Placement Landing Page Agency

    Insertion Order Message Campaign Proposition Desk Conversion Contact CDR
  16. 41.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Lead Lead
  17. 42.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Lead Lead
  18. 43.

    MarkeCng Creative Catalog Campaign Management Optimization Lead Sales Commissions Optimization

    CRM Lead Desks Telephony Support Contracts Billing Identity & Access
  19. 45.

    Bounded Context Consistency boundary of the language / model Define

    the biggest valid monoliths Required decomposition boundary
  20. 47.

    Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone

    Asset Publisher Target Market Campaign Website Placement Funnel MarkeCng Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Bounded Contexts? No Subdomains? EnCCes?
  21. 48.

    Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone

    Asset Publisher Target Market Campaign Website Placement Funnel MarkeCng Creative Catalog Contracts Billing Campaign Management Identity & Access Optimization Bounded Contexts? No Subdomains? EnCCes?
  22. 50.

    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
  23. 51.

    “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
  24. 60.

    Microservice = Microinterface Reducing coupling between services Limits reasons for

    change Easier to understand Better fault isolation More autonomy between services
  25. 61.

    Microservice & Databases Microservices should own its database No external

    access Access through Microservice’s API only Database = infinite interface!
  26. 62.
  27. 64.
  28. 65.
  29. 66.
  30. 67.
  31. 68.
  32. 69.
  33. 71.

    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.
  34. 75.

    Campaign Management Campaign Placement Funnel Banner Landing Page Website Zone

    Asset Publisher Target Market Campaign Website Placement Funnel Subdomains? EnCCes?
  35. 76.
  36. 77.
  37. 78.

    ”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
  38. 79.

    ”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
  39. 80.

    ”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
  40. 81.

    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
  41. 83.

    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
  42. 84.

    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
  43. 85.

    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.
  44. 86.

    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?
  45. 88.

    HeurisCc #1: Decompose to Bounded Contexts Do not implement conflicting

    models in the same service. 
 Always decompose to Bounded Contexts.
  46. 89.

    HeurisCc #2: Don’t ”First Law of Distributed Object Design: 


    “Don’t distribute your objects” MarCn Fowler
  47. 96.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  48. 97.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  49. 98.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  50. 99.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  51. 100.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  52. 101.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  53. 102.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  54. 103.

    MarkeCng Sales Commissions Desks Optimization CRM Telephony Creative Catalog Contracts

    Billing Campaign Management Identity & Access Optimization Identity & Access Generic
  55. 107.

    MarkeCng Sales Commissions Desks Sales
 Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core
  56. 108.

    MarkeCng Sales Commissions Desks Sales
 Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core
  57. 109.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core
  58. 110.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core
  59. 111.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core
  60. 112.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core
  61. 114.

    HeurisCc #4: Core Subdomains - Don’t Rush Adhere to subdomain’s

    boundaries. Decompose further only when you acquire domain knowledge.
  62. 116.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  63. 117.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  64. 118.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  65. 119.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  66. 120.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  67. 121.

    MarkeCng Sales Commissions Desks Sales Optimization CRM Telephony Creative Catalog

    Contracts Billing Campaign Management Identity & Access Ad Optimization Identity & Access Generic Core Supporting
  68. 127.

    HeurisCc #6: Evaluate Consistency Requirements Read last write? - Two

    services, synchronous communication 
 Service A Method A 
 Service B Method B Sync call
  69. 128.

    HeurisCc #6: Evaluate Consistency Requirements Eventual consistency? - Two services,

    asynchronous communication 
 Service A Method A 
 Service B Method B Asynchronous Communication
  70. 129.

    HeurisCc #6: Evaluate Consistency Requirements Concurrency control? - Same service

    Read last write? - Two services, sync communication Eventual consistency? - Two services, async communication
  71. 130.
  72. 131.

    HeurisCc #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 …
  73. 132.

    HeurisCc #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) }
  74. 133.

    HeurisCc #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) }
  75. 138.
  76. 149.

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

    decoupled? Should be the same service? HeurisCc #9: Evaluate Reasons for Change
  77. 150.
  78. 155.

    1. A service is a unit of func/onality exposed to

    the world through its public interface. 2. A microservice is a service with micro interface 3. The “micro-interface” is rela/ve to the use cases of the system that the service is a part of
  79. 156.

    Heuris/c #1: Always decompose to Bounded Contexts Heuris/c #2: Don’t

    go further, unless you have to Heuris/c #3: Buy/adopt generic subdomains Heuris/c #4: Core subdomains - don’t rush Heuris/c #5: Suppor/ng subdomains can be decomposed early
  80. 157.

    Heuris/c #6: Evaluate Consistency Requirements Heuris/c #7: Private / Public

    Events Heuris/c #8: Explicitly Define Events Heuris/c #9: Evaluate Reasons for Change Heuris/c #10: Evaluate Services’ “Doors”
  81. 159.

    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. Implemen/ng Domain-Driven Design, Vaughn Vernon 6. Enterprise Integra/on 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 Applica/on Architecture, Mar/n 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