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Hiding The Lead: Coupling, cohesion and microservices
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.
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Introduction to hiding the lead in coupling, cohesion, and microservices. Discusses independent deployability of services like Inventory and Shipping.
Focus on modules and their structure for independent and reusable working. Importance of module communication through network calls.
Legislation of information hiding to define module boundaries, the importance of maintaining internal implementation secrecy.
Explains accidental breakage in code due to unclear definitions and changing dependencies within modules.
Definition of Data Transfer Objects (DTOs) and their role in reducing dependencies and facilitating data operations.
Discussion on connections between modules, based on assumptions, and importance of explicit contracts to reduce dependencies.
Use of schemas for compatibility checking and promoting better testing practices in microservices design.
Defines coupling and cohesion, emphasizing their roles in module interactions and system stability.
Various types of coupling: domain, common, and content coupling. Discusses implications on information hiding and service flexibility.Reinforces the importance of information hiding, types of coupling, and strong cohesion for effective independent deployability.
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Hiding The Lead: Coupling, cohesion and microservices
- 1. HIDING THE LEAD COUPLING,COHESION AND MICROSERVICES Sam Newman https://www.flickr.com/photos/spongebabyalwaysfull/8793058944/
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- 7. @samnewman Customer Service Accounts v1 Independent deployability requires interfacestability Maintaining backwards compatibility is key
- 8. @samnewman Customer Service Accounts v2 Independent deployability requires interfacestability Maintaining backwards compatibility is key
- 9. @samnewman Customer Service Accounts v2 Independent deployability requires interfacestability Maintaining backwards compatibility is key
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- 12. @samnewman MODULES Module A Module D ModuleB Module C Module E
- 13. @samnewman MODULES Module A Module D ModuleB Module C Module E Allow for independent working
- 14. @samnewman MODULES Module A Module D ModuleB Module C Module E Allow for independent working And reuse
- 15. @samnewman MODULES Module A Module D ModuleB Module C Module E Allow for independent working And reuse Namespaces, packages
- 16. @samnewman MODULES Module A Module D ModuleB Module C Module E Allow for independent working And reuse Namespaces, packages NPMs, Gems, JARs etc
- 17. @samnewman AND MICROSERVICES? Module A ModuleDModule B Module C Module E
- 18. @samnewman AND MICROSERVICES? Module A ModuleDModule B Module C Module E “Modules” run on different computers
- 19. @samnewman AND MICROSERVICES? Module A ModuleDModule B Module C Module E Communication between modules is done via network calls “Modules” run on different computers
- 20. @samnewman AND MICROSERVICES? Module A ModuleDModule 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 doneright, are a form of modular architecture
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- 25. @samnewman INFORMATION HIDING http://repository.cmu.edu/cgi/viewcontent.cgi?article=2979&context=compsci Published in1971 Looked at how best to define module boundaries
- 26. @samnewman INFORMATION HIDING http://repository.cmu.edu/cgi/viewcontent.cgi?article=2979&context=compsci Published in1971 Looked at how best to define module boundaries Found that “information hiding” worked best
- 27. @samnewman INFORMATION HIDING ANDMICROSERVICES https://blog.acolyer.org/2016/09/05/on-the-criteria-to-be-used-in-decomposing-systems-into-modules/
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- 30. @samnewman Accounts NOT HIDING? Shipping If anupstream consumer can reach into your internal implementation..
- 31. @samnewman Accounts NOT HIDING? Shipping If anupstream 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 anupstream 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 anupstream consumer can reach into your internal implementation.. …then you can’t change this implementation without breaking the consumer
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- 36. @samnewman HIDING! Accounts Shipping Hide your secrets! Beexplicit about what is shared, and what is hidden Hidden
- 37. @samnewman HIDING! Accounts Shipping Hide your secrets! Beexplicit about what is shared, and what is hidden Shared Hidden
- 38. @samnewman HIDING! Accounts Shipping Hide your secrets! Beexplicit about what is shared, and what is hidden Shared Hidden
- 39. @samnewman HIDING! Accounts Shipping Hide your secrets! Beexplicit about what is shared, and what is hidden Shared Hidden Hidden things can change, shared things can’t
- 40. @samnewman ACCIDENTAL BREAKAGE public classCustomer { private int id; private String name; private int age; … } Code
- 41. @samnewman ACCIDENTAL BREAKAGE public classCustomer { private int id; private String name; private int age; … } Code
- 42. @samnewman ACCIDENTAL BREAKAGE public classCustomer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON
- 43. @samnewman ACCIDENTAL BREAKAGE public classCustomer { private int id; private String name; private int age; … } Code { “id” : 123, “name” : “sam”, “age” : 15 } JSON
- 44. @samnewman ACCIDENTAL BREAKAGE public classCustomer { 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 classCustomer { 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 classCustomer { 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
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- 48. @samnewman DATA TRANSFER OBJECT https://martinfowler.com/eaaCatalog/dataTransferObject.html Customer publicclass Customer { private int id; private String name; private LocalDate dob; … }
- 49. @samnewman DATA TRANSFER OBJECT https://martinfowler.com/eaaCatalog/dataTransferObject.html Customer publicclass 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 publicclass 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
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- 52. @samnewman AND CONNECTIONS BETWEENTHEM? “The connections between modules are the assumptions which the modules make about each other.” - David Parnas
- 53. @samnewman AND CONNECTIONS BETWEENTHEM? “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
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- 56. @samnewman EXPLICIT CONTRACTS? Module DModuleB Need an explicit understanding of the assumptions of consumers
- 57. @samnewman EXPLICIT CONTRACTS? Module DModuleB 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 DModuleB Need an explicit understanding of the assumptions of consumers To help us understand what can change easily, and what cannot Schemas can help!
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- 62. @samnewman And of coursetesting…
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- 67. @samnewman COUPLING AND COHESION CouplingCohesion Low
- 68. @samnewman COUPLING AND COHESION CouplingCohesion Low Strong
- 69. @samnewman COHESION The code thatchanges together, stays together
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- 72. @samnewman COUPLING The degree towhich changing one module requires a change in another
- 73. @samnewman CONSTANTINE’S LAW “A structureis stable if cohesion is strong and coupling is low.” - Albert Endres and Dieter Rombach
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- 77. @samnewman TYPES OF COUPLING DomainCommonTramp
- 78. @samnewman TYPES OF COUPLING DomainCommon ContentTramp
- 79. @samnewman TYPES OF COUPLING DomainCommon ContentTramp
- 80. @samnewman TYPES OF COUPLING DomainCommon Content Increasing coupling Tramp
- 81. @samnewman DOMAIN COUPLING Order Processor Warehouse ReserveStock Payment Take Payment
- 82. @samnewman DOMAIN COUPLING Order Processor Warehouse ReserveStock Payment Take Payment Domain Coupling
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- 86. @samnewman Order Processor Warehouse ShippingManifest Send Order Request # Item ID 3 2231 2 134 TRAMP COUPLING
- 87. @samnewman Order Processor Shipping Warehouse Shipping Manifest SendOrder Request # Item ID 3 2231 2 134 TRAMP COUPLING
- 88. @samnewman Order Processor Shipping Warehouse Shipping Manifest SendOrder Request # Item ID 3 2231 2 134 TRAMP COUPLING Shipping Manifest Dispatch Package Request
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- 91. @samnewman AVOIDING TRAMP COUPLING OrderProcessor Warehouse
- 92. @samnewman AVOIDING TRAMP COUPLING OrderProcessor Warehouse Send Order Request # Item ID 3 2231 2 134
- 93. @samnewman AVOIDING TRAMP COUPLING OrderProcessor Shipping Warehouse Send Order Request # Item ID 3 2231 2 134
- 94. @samnewman AVOIDING TRAMP COUPLING OrderProcessor 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
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- 99. @samnewman COMMON COUPLING Warehouse Stock LevelsOrder Processor
- 100. @samnewman COMMON COUPLING Warehouse Stock LevelsOrder ProcessorForecasting
- 101. @samnewman COMMON COUPLING Warehouse Stock LevelsOrder ProcessorForecasting Change to the common data impacts multiple microservices
- 102. @samnewman CONTENT COUPLING Order IDStatus 123 PLACED 456 SHIPPED
- 103. @samnewman CONTENT COUPLING Order IDStatus 123 PLACED 456 SHIPPED Order Processor
- 104. @samnewman CONTENT COUPLING Order IDStatus 123 PLACED 456 SHIPPED WarehouseOrder Processor
- 105. @samnewman CONTENT COUPLING Order IDStatus 123 PLACED 456 SHIPPED WarehouseOrder Processor Information hiding bypassed
- 106. @samnewman CONTENT COUPLING Order IDStatus 123 PLACED 456 SHIPPED WarehouseOrder Processor Information hiding bypassed Unclear what can safely be changed in the Order service
- 107. @samnewman CONTENT COUPLING Order IDStatus 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 DomainCommon ContentTramp
- 109. @samnewman TYPES OF COUPLING DomainCommon Content Increasing coupling Tramp
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- 111. @samnewman IN SUMMARY Information hidingis super important
- 112. @samnewman IN SUMMARY Information hidingis super important Some coupling is worse than others
- 113. @samnewman IN SUMMARY Information hidingis super important Some coupling is worse than others Information hiding, low coupling, strong cohesion = Independent Deployability
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