Hiding The Lead: Coupling, cohesion and microservices
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The document discusses the principles of microservices architecture as articulated by Sam Newman, emphasizing the importance of information hiding, independent deployability, and managing coupling and cohesion among modules. It highlights the need for explicit contracts and schemas to define module boundaries and minimize assumptions between them, thereby facilitating easier changes without breaking dependencies. Lastly, it underscores that low coupling and strong cohesion are crucial for achieving independent deployability in microservices.
Hiding The Lead: Coupling, cohesion and microservices
- 1. HIDING THE LEAD COUPLING, COHESION AND MICROSERVICES Sam Newman https://www.flickr.com/photos/spongebabyalwaysfull/8793058944/
- 7. @samnewman Customer Service Accounts v1 Independent deployability requires interface stability Maintaining backwards compatibility is key
- 8. @samnewman Customer Service Accounts v2 Independent deployability requires interface stability Maintaining backwards compatibility is key
- 9. @samnewman Customer Service Accounts v2 Independent deployability requires interface stability Maintaining backwards compatibility is key
- 12. @samnewman MODULES Module A Module D Module B Module C Module E
- 13. @samnewman MODULES Module A Module D Module B Module C Module E Allow for independent working
- 14. @samnewman MODULES Module A Module D Module B Module C Module E Allow for independent working And reuse
- 15. @samnewman MODULES Module A Module D Module B Module C Module E Allow for independent working And reuse Namespaces, packages
- 16. @samnewman MODULES Module A Module D Module B Module C Module E Allow for independent working And reuse Namespaces, packages NPMs, Gems, JARs etc
- 17. @samnewman AND MICROSERVICES? Module A Module DModule B Module C Module E
- 18. @samnewman AND MICROSERVICES? Module A Module DModule B Module C Module E “Modules” run on different computers
- 19. @samnewman AND MICROSERVICES? Module A Module DModule B Module C Module E Communication between modules is done via network calls “Modules” run on different computers
- 20. @samnewman AND MICROSERVICES? Module A Module DModule B Module C Module E Communication between modules is done via network calls “Modules” run on different computers Allows for easier independent deployability
- 21. @samnewman Microservices, when done right, are a form of modular architecture
- 25. @samnewman INFORMATION HIDING http://repository.cmu.edu/cgi/viewcontent.cgi?article=2979&context=compsci Published in 1971 Looked at how best to define module boundaries
- 26. @samnewman INFORMATION HIDING http://repository.cmu.edu/cgi/viewcontent.cgi?article=2979&context=compsci Published in 1971 Looked at how best to define module boundaries Found that “information hiding” worked best
- 27. @samnewman INFORMATION HIDING AND MICROSERVICES https://blog.acolyer.org/2016/09/05/on-the-criteria-to-be-used-in-decomposing-systems-into-modules/
- 30. @samnewman Accounts NOT HIDING? Shipping If an upstream consumer can reach into your internal implementation..
- 31. @samnewman Accounts NOT HIDING? Shipping If an upstream consumer can reach into your internal implementation.. …then you can’t change this implementation without breaking the consumer
- 32. @samnewman Accounts NOT HIDING? Shipping If an upstream consumer can reach into your internal implementation.. …then you can’t change this implementation without breaking the consumer
- 33. @samnewman Accounts NOT HIDING? Shipping If an upstream consumer can reach into your internal implementation.. …then you can’t change this implementation without breaking the consumer
- 36. @samnewman HIDING! Accounts Shipping Hide your secrets! Be explicit about what is shared, and what is hidden Hidden
- 37. @samnewman HIDING! Accounts Shipping Hide your secrets! Be explicit about what is shared, and what is hidden Shared Hidden
- 38. @samnewman HIDING! Accounts Shipping Hide your secrets! Be explicit about what is shared, and what is hidden Shared Hidden
- 39. @samnewman HIDING! Accounts Shipping Hide your secrets! Be explicit about what is shared, and what is hidden Shared Hidden Hidden things can change, shared things can’t
- 40. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code
- 41. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code
- 42. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON
- 43. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON
- 44. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON public class Customer { private int id; private String name; private LocalDate dob; … } Code
- 45. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON public class Customer { private int id; private String name; private LocalDate dob; … } Code
- 46. @samnewman ACCIDENTAL BREAKAGE public class Customer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON public class Customer { private int id; private String name; private LocalDate dob; … } Code { “id” : 123, “name” : “sam”, “dob” : 15/02/1974 } JSON
- 48. @samnewman DATA TRANSFER OBJECT https://martinfowler.com/eaaCatalog/dataTransferObject.html Customer public class Customer { private int id; private String name; private LocalDate dob; … }
- 49. @samnewman DATA TRANSFER OBJECT https://martinfowler.com/eaaCatalog/dataTransferObject.html Customer public class Customer { private int id; private String name; private LocalDate dob; … } public class CustomerDTO { private int id; private String name; private int age; … }
- 50. @samnewman DATA TRANSFER OBJECT https://martinfowler.com/eaaCatalog/dataTransferObject.html Customer public class Customer { private int id; private String name; private LocalDate dob; … } public class CustomerDTO { private int id; private String name; private int age; … } { “id” : 123, “name” : “sam”, “age” : 15 } JSON
- 51. @samnewman AND CONNECTIONS BETWEEN THEM?
- 52. @samnewman AND CONNECTIONS BETWEEN THEM? “The connections between modules are the assumptions which the modules make about each other.” - David Parnas
- 53. @samnewman AND CONNECTIONS BETWEEN THEM? “The connections between modules are the assumptions which the modules make about each other.” - David Parnas Information hiding is about reducing the assumptions one module has for another
- 56. @samnewman EXPLICIT CONTRACTS? Module DModule B Need an explicit understanding of the assumptions of consumers
- 57. @samnewman EXPLICIT CONTRACTS? Module DModule B Need an explicit understanding of the assumptions of consumers To help us understand what can change easily, and what cannot
- 58. @samnewman EXPLICIT CONTRACTS? Module DModule B Need an explicit understanding of the assumptions of consumers To help us understand what can change easily, and what cannot Schemas can help!
- 62. @samnewman And of course testing…
- 66. @samnewman COUPLING AND COHESION Coupling Cohesion
- 67. @samnewman COUPLING AND COHESION Coupling Cohesion Low
- 68. @samnewman COUPLING AND COHESION Coupling Cohesion Low Strong
- 69. @samnewman COHESION The code that changes together, stays together
- 72. @samnewman COUPLING The degree to which changing one module requires a change in another
- 73. @samnewman CONSTANTINE’S LAW “A structure is stable if cohesion is strong and coupling is low.” - Albert Endres and Dieter Rombach
- 76. @samnewman TYPES OF COUPLING Domain Tramp
- 77. @samnewman TYPES OF COUPLING Domain CommonTramp
- 78. @samnewman TYPES OF COUPLING Domain Common ContentTramp
- 79. @samnewman TYPES OF COUPLING Domain Common ContentTramp
- 80. @samnewman TYPES OF COUPLING Domain Common Content Increasing coupling Tramp
- 81. @samnewman DOMAIN COUPLING Order Processor Warehouse Reserve Stock Payment Take Payment
- 82. @samnewman DOMAIN COUPLING Order Processor Warehouse Reserve Stock Payment Take Payment Domain Coupling
- 85. @samnewman Order Processor Warehouse TRAMP COUPLING
- 86. @samnewman Order Processor Warehouse Shipping Manifest Send Order Request # Item ID 3 2231 2 134 TRAMP COUPLING
- 87. @samnewman Order Processor Shipping Warehouse Shipping Manifest Send Order Request # Item ID 3 2231 2 134 TRAMP COUPLING
- 88. @samnewman Order Processor Shipping Warehouse Shipping Manifest Send Order Request # Item ID 3 2231 2 134 TRAMP COUPLING Shipping Manifest Dispatch Package Request
- 90. @samnewman AVOIDING TRAMP COUPLING Order Processor
- 91. @samnewman AVOIDING TRAMP COUPLING Order Processor Warehouse
- 92. @samnewman AVOIDING TRAMP COUPLING Order Processor Warehouse Send Order Request # Item ID 3 2231 2 134
- 93. @samnewman AVOIDING TRAMP COUPLING Order Processor Shipping Warehouse Send Order Request # Item ID 3 2231 2 134
- 94. @samnewman AVOIDING TRAMP COUPLING Order Processor Shipping Warehouse Shipping Manifest Send Order Request # Item ID 3 2231 2 134
- 95. @samnewman AVOIDING TRAMP COUPLING (CONT) Order Processor Warehouse Shipping 1342 22313 ItemID# Send Order Request Shipping Manifest Dispatch Package Request 123 The Place, UK Express Shipping
- 99. @samnewman COMMON COUPLING Warehouse Stock Levels Order Processor
- 100. @samnewman COMMON COUPLING Warehouse Stock Levels Order ProcessorForecasting
- 101. @samnewman COMMON COUPLING Warehouse Stock Levels Order ProcessorForecasting Change to the common data impacts multiple microservices
- 102. @samnewman CONTENT COUPLING Order ID Status 123 PLACED 456 SHIPPED
- 103. @samnewman CONTENT COUPLING Order ID Status 123 PLACED 456 SHIPPED Order Processor
- 104. @samnewman CONTENT COUPLING Order ID Status 123 PLACED 456 SHIPPED WarehouseOrder Processor
- 105. @samnewman CONTENT COUPLING Order ID Status 123 PLACED 456 SHIPPED WarehouseOrder Processor Information hiding bypassed
- 106. @samnewman CONTENT COUPLING Order ID Status 123 PLACED 456 SHIPPED WarehouseOrder Processor Information hiding bypassed Unclear what can safely be changed in the Order service
- 107. @samnewman CONTENT COUPLING Order ID Status 123 PLACED 456 SHIPPED WarehouseOrder Processor Information hiding bypassed Unclear what can safely be changed in the Order service Aka Pathological Coupling
- 108. @samnewman TYPES OF COUPLING Domain Common ContentTramp
- 109. @samnewman TYPES OF COUPLING Domain Common Content Increasing coupling Tramp
- 111. @samnewman IN SUMMARY Information hiding is super important
- 112. @samnewman IN SUMMARY Information hiding is super important Some coupling is worse than others
- 113. @samnewman IN SUMMARY Information hiding is super important Some coupling is worse than others Information hiding, low coupling, strong cohesion = Independent Deployability