Breaking down problems

When starting with microservice architectures a common question people ask is "how big should a service be?” While this is sometimes useful when considering the complexity of a system, it doesn’t capture the variety of use cases or problems systems may be solving — a service that selects emoji for push notifications will probably be simpler than one of the core services in a payment processor?

In this talk we’ll look at how Monzo approach problem solving, taking business ideas and breaking them down into small, simple, services which together build a system that is more than the sum of its parts.

Transcript

1. Breaking down problems Building systems of systems with microservices at Monzo 
 @mattheath
2. Hi, I’m Matt
3. @mattheath
6. 16:02 Wednesday 29 May
7. Nov 2015 May 2019 Fastest growing UK Bank
 2m customers 40k a week
12. LICENCE WITH RESTRICTIONS WE ARE HERE A UK banking licence is authorised by the PRA and regulated by the PRA and FCA1, allowing deposit- taking and balance sheet lending. Once granted, it allows firms to passport across Europe, accessing This is followed by a “mobilisation” phase during which final capital is raised and IT systems are completed, before launching to the public. We received a UK banking licence in August 2016! FEB 2015 JAN 2016 JAN 2017 MAR FEB FEB APR MAR MAR APR MAY JUN JUL MAY APR JUN MAY JUL JUN AUG JUL SEP AUG NOV SEP DEC NOV DEC PRE APPLICATION APPLICATION MOBILISATION LAUNCH LICENCE WITH RESTRICTIONS 50K MAX DEPOSIT WE ARE HERE A UK banking licence is authorised by the PRA and regulated by the PRA and FCA1, allowing deposit- taking and balance sheet lending. Once granted, it allows firms to passport across Europe, accessing This is followed by a “mobilisation” phase during which final capital is raised and IT systems are completed, before launching to the public. We received a UK banking licence in August 2016! JAN 2016 JAN 2017 MAR FEB FEB APR MAR MAR APR MAY JUN JUL MAY APR JUN MAY JUL JUN AUG JUL SEP AUG NOV SEP DEC NOV DEC E APPLICATION APPLICATION MOBILISATION LAUNCH LICENCE WITH RESTRICTIONS WE ARE HERE AUG
 2016 JAN
 2016 Feb
 2015 APR
 2017 A UK banking licence is authorised by the PRA and regulated by the PRA and FCA1, allowing deposit- taking and balance sheet lending. Once granted, it allows firms to passport across Europe, accessing This is followed by a “mobilisation” phase during which final capital is raised and IT systems are completed, before launching to the public. We received a UK banking licence in August 2016! FEB 2015 JAN 2016 JAN 2017 MAR FEB FEB APR MAR MAR APR MAY APR JUN MAY JUL JUN AUG JUL SEP AUG NOV SEP DEC NOV DEC PRE APPLICATION APPLICATION MOBILISATION LICENCE WITH RESTRICTIONS WE ARE HERE
13. Henrik Kniberg
14. Henrik Kniberg
15. James Leah Matt
16. James Leah Matt
17. James Leah Matt
22. X X X
26. ☕☕
27. ☕☕
28. Payment API Ledger
29. Payment API Ledger Database
30. Transactions Payment API Ledger
31. Transactions Payment API Ledger Accounts
32. Payment API Transactions Ledger Accounts Cassandra Database
33. Payment API Transactions Ledger Accounts Cassandra Database ? ? ? ? ? ? ? ? ?
34. Henrik Kniberg
40. Payment API Transactions Ledger Accounts Cassandra Database
41. Card API Payment API Transactions Ledger Accounts Cassandra Database
42. IT’S REAL!
50. Feb 2015 May 2019 monzo services
51. 1136 Feb 2015 May 2019 monzo services
52. Why do we break down problems?
56. Why do we break down problems? Manage risk , Scale organisations Use the best tools for the job
57. Why do we break down problems? Manage risk , Scale organisations Use the best tools for the job
58. Managing risk ⚠ Are we building the right thing? ⚠ Will we hit deadlines?
59. Henrik Kniberg
60. Guiding Principle: 
 Ship it, and iterate.
61. Guiding Principle: 
 Make changes small, make them often
62. Why do we break down problems? Manage risk Use the best tools for the job , Scale organisations
63. Why do we break down problems? Manage risk Use the best tools for the job , Scale organisations
64. How do we break down problems?
65. Dividing features up
66. Henrik Kniberg
67. Split by domain
68. Split by domain users transactions faster payments card payments cards accounts addresses profiles feature flags points pots direct debits
69. Split by responsibility
70. Split by responsibility card management customer
 signup clearing
 processing reconciliation pots accounts authentication authorisation bank
 statements message signing
71. Guiding Principle: 
 Do one thing, do it well.
72. Examples:
 Building APIs
75. API
76. API
77. API Service API Service API Service API Service API Service API Service API Service API Service Edge Gateway
79. Accounts Cards Pots Feed Payments … Edge Gateway
80. Edge Gateway Accounts Cards Pots Payments … New
 Exciting
 API!! Feed
81. Cards Pots Payments … Accounts New
 Exciting
 API!! Feed Edge Gateway
82. Cards Pots Payments … Accounts New
 Exciting
 API!! Feed Edge Gateway
83. Edge Gateway Accounts Cards Pots Payments … New
 Exciting
 API!! Feed
84. Isolate failure Make changes small, make them often Ship it, and iterate , Scale teams and organisations
85. Single responsibility
86. Load Balancer Edge Gateway
87. Load Balancer Edge Gateway API Service
88. Service A Load Balancer Edge Gateway API Service
89. Service A Service B Load Balancer Edge Gateway API Service
90. Service A Service B Load Balancer Edge Gateway API Service Responsible for external interface Responsible for domain logic Responsible for routing
91. Manage complexity
92. Account
 Service Load Balancer Edge Gateway Account
 API
93. Account
 Service Load Balancer Edge Gateway Account
 API Account
 Number
 Service
94. Account
 Service Load Balancer Edge Gateway Account
 API Account
 Number
 Service IBAN
 Service
95. Account
 Service Load Balancer Edge Gateway Account
 API Account
 Number
 Service IBAN
 Service Account service responsibility remains unchanged, even as overall system complexity increases
96. Account
 Service Load Balancer Edge Gateway Account
 API Account
 Number
 Service IBAN
 Service Additional, simple, services solve related but separate problems
97. Account
 Service Load Balancer Edge Gateway Account
 API Account
 Number
 Service IBAN
 Service
98. Account
 Service Load Balancer Edge Gateway Account
 API Account
 Number
 Service IBAN
 Service Euro
 Payment
 Services 5
99. Account
 Service Account
 Number
 Service IBAN
 Service Euro
 Payment
 Services 5 Decoupling more specialised behaviour keeps services simple 6
100. Account
 Service Account
 Number
 Service IBAN
 Service Euro
 Payment
 Services 5 Faster
 Payment
 Services 6
101. Account
 Service Account
 Number
 Service IBAN
 Service Euro
 Payment
 Services 5 Faster
 Payment
 Services 6
102. Account
 Service Account
 Number
 Service IBAN
 Service Euro
 Payment
 Services 5 Faster
 Payment
 Services 6 Isolating failure along domain boundaries improves availability
103. Managing Complexity
104. Guiding Principle: 
 Simplicity
105. https://xkcd.com/927/
106. Feb 2015 May 2019 monzo services
107. Feb 2015 May 2019 monzo services The Refactathon https://monzo.com/blog/2018/12/04/refactoring-old-code/
108. 8 Identify areas of complexity and debt ⏱ Make time to improve these Teams move faster as a result
109. Guiding Principle: 
 Standardisation
110. Build on abstractions
111. instance instance instance instance instance instance
112. instance instance instance instance instance instance Kubernetes
113. kubernetes
114. kubernetes service service service service service service service service service service service service service
115. kubernetes service Prometheus service service Kafka envoy Kafka service service Elasticsearch calico API service
116. Service Service Reliable inter-service
 communication offloaded to Envoy, simplifying services
117. API Service Service A Service B Load Balancer Edge Gateway Service D Service D Service C Event based communication decouples services, lets us build reliable pipelines, and helps isolate failure
118. Simple systems are more reliable Small systems are faster to iterate Failure can be isolated and constrained
119. Standardisation makes everything easier Onboard new people quickly People feel empowered and productive Build reliable systems, faster.
121. monzo.com/careers