1. 1. Watch your communication How communication drives designUwe Friedrichsen codecentric AG 2016
2. 2. @ufried Uwe Friedrichsen | uwe.friedrichsen@codecentric.de | http://slideshare.net/ufried | http://ufried.tumblr.com
3. 3. The one-size-fits-all trap
4. 4. Standardization as a virtue
5. 5. We see that a lot One programming language One framework One build system One type of runtime unit One data store One type of database access One application server One ... One communication paradigm
6. 6. Why are we doing it?
7. 7. Reducing complexity Avoid intellectual overload Easier to understand Easier to change Faster to change Easier to operate Less error-prone Cheaper
8. 8. These are valid and important reasons
9. 9. ... but that is just one side of the coin
10. 10. The complexity of a solution must match the complexity of the problem to solve
11. 11. If your task is to build a box from pre-cut boards, only using a hammer might be adequate
12. 12. If your task is also to paint the box you just built, only having a hammer might be a problem
13. 13. Now imagine building a whole house just with a hammer
14. 14. Yet, in IT we often tend to build whole houses just with a hammer because boxes can be built with a hammer
15. 15. Complexity mismatch means Increased accidental complexity Harder to understand Harder to change Slower to change Harder to operate More error-prone More expensive
16. 16. Complexity Essential complexity Adds direct accidental complexity Problem complexity Ideal solution complexity Adds indirect accidental complexity
17. 17. Complexity Problem complexity Overly complex solution Increased accidental complexity More tooling than needed to get the job done well
18. 18. Complexity Problem complexity Over- simplified solution Increased accidental complexity Not enough tooling to get the job done well
19. 19. Overall Solution Complexity :=Essential Problem Complexity +Solution Complexity Mismatch Solution Complexity Mismatch a.k.a. Accidental ComplexityBe aware that mismatch in both directions adds to overall solution complexity
20. 20. Complexity Essential complexity Problem complexity Aim for the least complex solution with respect to the problem you have to solve(Yes, it is about trade-offs as always in architecture)
21. 21. Communication paradigms
22. 22. Communication paradigms Dimensions of communication Synchronous vs. asynchronous Request/response vs. message passing Commands, Events and Documents Sender/Receiver dependency
23. 23. Communication paradigms Typical communication patterns Synchronous request/response Asynchronous commands (with known receiver) Asynchronous events (without known receiver)
24. 24. The synchronous request/response everywhere trap
25. 25. Why are we doing it?
26. 26. Remember the one-size-fits-all trap?
27. 27. Yes, but why this paradigm?
28. 28. Why synchronous R/R? Its how the internet works The library support is better It is easier to reason about Matches the way we consciously think Matches the way we learned to do design
29. 29. Do not forget the other side of the coin
30. 30. The flipside of the coin HTTP was designed for a specific use case Access hypermedia content Not an ubiquitous communication solution The world outside a process is different Non-determinism kills easy reasoning Latency creep kills easy reasoning Solution mismatch adds complexity Compromises functional encapsulation Changes and extensions become more complicated Longer activation paths compromise robustness
31. 31. Designing communication
32. 32. An (invidious) example
33. 33. Order fulfillment
34. 34. Let us begin with the well-known synchronous request/response design ...
35. 35. Order fulfillmentInitial version with limited functionality Order includes Items Amounts Price per item Total price Credit card payment Only non-digital items
36. 36. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Credit Card Coordinate Warehouse
37. 37. Order fulfillmentAdd coupons Order additionally includes Optional coupon ID Optional remaining coupon value Coupon is already charged against total price Validate coupon
38. 38. Order Fulfillment Service Online Shop Payment Service Shipment Service Warehouse System Coupon Management CouponCredit Card Coordinate Warehouse Coordinate Credit Card Provider
39. 39. Order fulfillmentAdd promotions Order additionally includes Optional promotion ID Promotion is already applied to order Notify Campaign Management System about promotion usage
40. 40. Order Fulfillment Service Online Shop Payment Service Shipment Service Warehouse System Coupon Management Coupon Campaign Management Promotion Credit Card Coordinate Warehouse Coordinate Credit Card Provider
41. 41. Order fulfillmentAdd customer accounts Order additionally includes Payment type (Credit card/Account) Charge customer account
42. 42. Order Fulfillment Service Online Shop Payment Service Shipment Service Warehouse System Coupon Management Campaign Management Account service Accounts Receivables Coordinate Warehouse Credit Card Provider Coupon Promotion Credit Card Coordinate
43. 43. Order fulfillmentAdd PayPal Order additionally includes More payment types (Credit card/PayPal/Account) Payment via PayPal
44. 44. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Coupon Management Promotion Campaign Management Account service Payment provider PayPal Accounts Receivables Coupon Credit Card Coordinate Warehouse PayPal Coordinate
45. 45. Order fulfillmentAdd digital music library New shipment method Activate music assets in digital music library Notify customer via email including access link Digital music library has its own API
46. 46. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Coupon Management Promotion Campaign Management Account service Payment provider PayPal Accounts Receivables Music Library E-Mail Server Coupon Credit Card Coordinate Warehouse Coordinate Music Notify Cust. PayPal Coordinate
47. 47. Order fulfillmentAdd digital video library New digital shipment channel Activate video assets in digital video library Notify customer via email including access link Digital video library has its own API Different from the music library API
48. 48. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Coupon Management Promotion Campaign Management Account service Payment provider PayPal Accounts Receivables Music LibraryVideo Library E-Mail Server Coupon Credit Card Coordinate Warehouse Coordinate Assets Notify Cust. PayPal Coordinate
49. 49. Order fulfillmentAdd e-book library New digital shipment channel Activate e-books in e-book library Notify customer via email including access link E-Book library has its own API Different from the other asset library APIs
50. 50. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Coupon Management Promotion Campaign Management Account service Payment provider PayPal Accounts Receivables Music Library E-Book Library Video Library E-Mail Server Coupon Credit Card Coordinate Warehouse Coordinate Assets Notify Cust. PayPal Coordinate
51. 51. Order fulfillmentAdd bonus card Order additionally includes Optional bonus card ID Potential discount is already applied to order Notify Loyalty Management System about customer purchase
52. 52. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Coupon Management Promotion Campaign Management Loyalty Account service Payment provider PayPal Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server Coupon Credit Card Coordinate Warehouse Coordinate Assets Notify Cust. PayPal Coordinate
53. 53. Order fulfillmentMore requirements to come
54. 54. Order Fulfillment Service Online Shop Payment Service Credit Card Provider Shipment Service Warehouse System Coupon Management Promotion Campaign Management Loyalty Account service Payment provider PayPal Loyalty Management Accounts Receivables Music Library E-Book Library Video Library E-Mail Server Coupon Credit Card Coordinate Warehouse Coordinate Assets Notify Cust. PayPal Coordinate Synchronous request/response findingsDivide and conquer design Tight service coupling including cross-domain coupling Long activation paths Latency creep Availability erosion Underlying design assumption is 100% availability of all services used Complex orchestration logic in services including cross-service transactions New downstream services require changes of upstream services including knowledge about how to access downstream services in upstream services
55. 55. Let us repeat the design using asynchronous events ...
56. 56. Order fulfillment
57. 57. Order fulfillmentInitial version with limited functionality Order includes Items Amounts Price per item Total price Credit card payment Only non-digital items
58. 58. Order confirmed Online Shop Credit Card Provider Warehouse System Credit Card Service Warehouse Service Payment authorized Payment failed
59. 59. Order fulfillmentAdd coupons Order additionally includes Optional coupon ID Optional remaining coupon value Coupon is already charged against total price Validate coupon
60. 60. Order confirmed Online Shop Credit Card Provider Warehouse System Credit Card Service Warehouse Service Payment authorized Payment failed Coupon Management Coupon Service
61. 61. Order fulfillmentAdd promotions Order additionally includes Optional promotion ID Promotion is already applied to order Notify Campaign Management System about promotion usage
62. 62. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Credit Card Service Warehouse Service Promotion Service Coupon Service Payment authorized Payment failed
63. 63. Order fulfillmentAdd customer accounts Order additionally includes Payment type (Credit card/Account) Charge customer account
64. 64. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Warehouse Service Promotion Service Coupon Service Payment authorized Payment failed
65. 65. Order fulfillmentAdd PayPal Order additionally includes More payment types (Credit card/PayPal/Account) Payment via PayPal
66. 66. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Payment authorized Payment failed
67. 67. Order fulfillmentAdd digital music library New shipment method Activate music assets in digital music library Notify customer via email including access link Digital music library has its own API
68. 68. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Music Library E-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Music Library Service Notification Service Payment authorizedDigital asset provisioned Payment failed
69. 69. Order fulfillmentAdd digital video library New digital shipment channel Activate video assets in digital video library Notify customer via email including access link Digital video library has its own API Different from the music library API
70. 70. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Music Library Video LibraryE-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Music Library Service Video Library Service Notification Service Payment authorizedDigital asset provisioned Payment failed
71. 71. Order fulfillmentAdd e-book library New digital shipment channel Activate e-books in e-book library Notify customer via email including access link E-Book library has its own API Different from the other asset library APIs
72. 72. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Accounts Receivables Music Library E-Book Library Video LibraryE-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Payment authorizedDigital asset provisioned Payment failed
73. 73. Order fulfillmentAdd bonus card Order additionally includes Optional bonus card ID Promotion is already applied to order Notify Loyalty Management System about customer purchase
74. 74. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Loyalty Management Accounts Receivables Music Library E-Book Library Video LibraryE-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Bonus Card Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Payment authorizedDigital asset provisioned Payment failed
75. 75. And how do we figure out if a business transaction eventually completes?
76. 76. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Loyalty Management Accounts Receivables Music Library E-Book Library Video LibraryE-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Bonus Card Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Order fulfillment supervisor Payment authorizedDigital asset provisioned Payment failed Track flow of events. Reschedule events in case of failure Services are responsible to eventually succeed or fail for good, usually incorporating a supervision/escalation hierarchy for that
77. 77. Order confirmed Online Shop Credit Card Provider Warehouse System Coupon Management Campaign Management Account service Credit Card Service Loyalty Management Accounts Receivables Music Library E-Book Library Video LibraryE-Mail Server PayPal PayPal Service Warehouse Service Promotion Service Bonus Card Service Coupon Service Music Library Service Video Library Service E-Book Library Service Notification Service Payment authorizedDigital asset provisioned Payment failed Order fulfillment supervisor Track flow of events Reschedule events in case of failure Services are responsible to eventually succeed or fail for good, usually incorporating a supervision/escalation hierarchy for that Asynchronous events findingsGo with the flow design Services and domains decoupled Very short activation paths High responsiveness High availability No design assumptions about availability of services Coordination via choreography No central coordination and cross-service transactions Instead functional compensation logic in external supervision service New services can be integrated without touching existing services Services only focus on their task (no knowledge about other services required)
78. 78. Didnt we miss any special cases that would lead to very different findings?
79. 79. Some special casesSynchronous request/response design Current order status E.g., pass status through call chain Maybe additionally extend order fulfillment service to store status in an status information database Payment failed E.g., stop processing in fulfillment service and send back appropriate status to online shop Cashing coupon failed E.g., extend payment service to place task in desk officers inbox Integrate new video library (different API) Adapt shipment service to new API Make sure not to disrupt other service aspects
80. 80. Some special casesAsynchronous events design Current order status E.g., track events with a new service and store them in an status information database Payment failed E.g., track dedicated event with a new service that notifies customer and/or online shop Cashing coupon failed E.g., send out dedicated event that a new service subscribes to New service then places task in desk officers inbox Integrate new video library (different API) Implement new service Replace existing service with new service
81. 81. Feels a lot like recurring patterns
82. 82. What did we learn so far?
83. 83. Comparing the paradigms Decomposition Vertically divide-and-conquer vs. horizontally go-with-the-flow Coordination Coordination logic/services and orchestration vs. event chains and choreography Transactions Built-in transaction handling vs. external supervision Error handling Built into service vs. escalation/supervision strategy Separation of concerns Multiple responsibilities service vs. single responsibility services Encapsulation Domain logic distributed across services vs. domain logic in one place Complexity A draw
84. 84. Different communication paradigms lead to very different service designs which means different options to address a given problem
85. 85. Related areas and limitations
86. 86. Mixing communication paradigms
87. 87. Mixing paradigms Always an option Note the trade-off between design purity and solution mismatch complexity A (very) simple heuristic Single functionality All-or-nothing characteristic Single domain Synchronous request/response Multiple functionalities Flow/Process characteristic Multiple domains Asynchronous messaging
88. 88. What if the paradigm is fixed?
89. 89. Fixed paradigm You can simulate other paradigms E.g., simulate sync. r/r with async. messaging E.g., simulate async. commands with sync. r/r Will support the service design topic Apart from that it is a (lame) compromise
90. 90. What about user interaction?
91. 91. User interaction Interaction with user client is usually r/r Use web sockets if available Use the mediator pattern with timeouts Could be implemented via a BFF service Complement with processing status page
92. 92. Can we apply the same patterns inside process boundaries?
93. 93. Inside process boundaries Have the process context in mind Without threads If your downstream call dies, you are also dead Usually synchronous r/r is appropriate Otherwise single-threaded scheduler is needed With threads Multi-process light Better multi-threading resilience possible More design options
94. 94. Wrap-up The one-size-fits-all trap Communication paradigms The synchronous-r/r-everywhere trap Designing communication Influence on service design Different communication paradigms lead to very different service designs
95. 95. There is no one-size-fits-all solution
96. 96. @ufried Uwe Friedrichsen | uwe.friedrichsen@codecentric.de | http://slideshare.net/ufried | http://ufried.tumblr.com