Is the monolith a problem? - Full version -

presented at wroclove.rb 2025 / record
presented at Baltic Ruby 2025

Duration: 35 mins

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1. Is the monolith a problem? Chikahiro Tokoro
2. The monolith was blamed for last decade… Not scalable Complex and hard to debug Deployment bottleneck Not clear boundary Difficult to maintain
3. The monolith was blamed for last decade… Not scalable Not clear boundary Difficult to maintain Deployment bottleneck Complex and hard to debug
4. ….and is the microservices a solution? ✅
5. Tobi Lutke (Shopify co-founder) - X Is the monolith, not scalable?
6. Is the monolith, deployment bottleneck? Interpreters Everywhere and All the Time - Stefan Marr, PLISS 2023
7. And Is the microservices, simple and easy to maintain?
9. BBC NEWS | UK | Magazine | The life cycle of a fashion trend
10. 2014 2025 2004 1998
11. Macro trends in the tech industry | April 2024 | Thoughtworks
12. Freedom Dumlao on X - 2024.09 Scaling up the Prime Video audio/video monitoring service and reducing costs by 90% - 2023
13. 2025 rails, ruby - Explore - Google Trends
14. rails, spring, nextjs, django, laravel - Explore - Google Trends 2025
15. Monolith / Microservices are the architectures which has own pros and cons
16. CI / Deployment Language Monolingual Multilingual Slow Fast Simple Complex Infrastructure Latency Tracing Scaling Boundary Low High Single instance Multiple instances Clear Vague scale up (vertical) high cost, limited, simple scale out (horizontal) low cost, unlimited, complex
17. Monday 3-2-1 Conway's law - refactoring.fm Microservices can be more related for autonomy / scalability of organization
18. Building Microservices, 2nd Edition - Sam Newman: 1. What Are Microservices? - Should I Use Microservices? 2000 engineers, 2 millions lines of code: the history of a Rails monolith - Cristian and Anatoly | EuRuKo 2024
19. Method call API call which can be failed 😱 Circuit Breaker Retry mechanism In order to use another component… Is it essential complexity? (never failed)
20. Is the monolith a problem? No Then what’s the problem?
21. Jason Warner (Github ex-CTO) - X
22. Modular Monolith
23. What’s the modular monolith? InfoQ: Monolith Decomposition Patterns - Sam Newman
24. Shopify/packwerk: Good things come in small packages
25. 2014 2025 2004 1998 Macro trends in the tech industry | April 2024 | Thoughtworks Modular Monolith
26. 2014 2025 2004 1998 Macro trends in the tech industry | April 2024 | Thoughtworks Modular Monolith
27. Eileen Uchitelle - The Myth of the Modular Monolith - Rails World 2024
28. High cohesion is necessary
29. God Object
30. This is a problem! God Object
31. Tight coupling / Poor cohesion Antipattern: Single object knows/does too much What’s the God Object (Class) ? Hard to change, buggy Not clear boundary / Tangling e.g. Changing User Registration logic break Payment feature 😱 (violating Open/Closed Principle) Ball of Mud
32. Example of God Object
33. Not scalable Deployment bottleneck ✅ ✅ The monolith was blamed for last decade… Difficult to maintain Complex and hard to debug Not clear boundary
34. Not scalable Deployment bottleneck ✅ Those are characteristics of God Object! The monolith was blamed for last decade… Difficult to maintain Complex and hard to debug Not clear boundary
35. Distributed Monolith
36. 2. Refactoring God Object 1. Better Model Design Where the God Object come from?
37. DRY ~ Don’t Repeat Yourself ~ “Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.“ NOT for the code!! 1. Better Model Design
38. Invoice Receipt Customer understand DRY Let’s DRY for duplicated code!!
39. understand DRY Customer Document type: invoice / receipt Invoice Receipt Receipt is issued after invoice was paid use STI
40. understand DRY Customer Invoice Receipt Invoice can only be issued for company Document type: invoice / receipt
41. understand DRY Customer Invoice Receipt Company After issuing invoice, it should generate PDF Document type: invoice / receipt
42. Document type: invoice / receipt understand DRY Customer Invoice Receipt Company pdf
43. understand DRY Customer Invoice Receipt Company pdf Document type: invoice / receipt
44. understand DRY Invoice Receipt Customer This is a similarity! Code duplication might be coincident Invoice and Receipt are different (domain) knowledge
45. understand DRY Customer Invoice Receipt Company pdf
46. Customer Invoice Receipt Company pdf Document type: invoice / receipt Customer Invoice Receipt Company pdf Modularity / Cohesion / (Domain) Boundary may appear naturally
47. DRY is about Knowledge | Mathias Verraes DRY + Domain-Driven Design 1. Better Model Design
48. 1. Better Model Design
49. User type: admin/customer/seller Admin Customer Seller Mixed model 1. Better Model Design
50. Article status: draft / scheduled / published Author Author DraftArticle Article Schedule Mixed model 1. Better Model Design
51. Order status: accepted / shipped Product Customer Domain crossing model Order Product Customer Shipment 1. Better Model Design
52. 2. Refactoring God Object 1. Better Model Design
53. Go with clear business merit Don’t underestimate, It takes time!!
54. Example: User Single Sign-On User type: admin/customer/seller User Application A New Application B
55. Example: User Single Sign-On User type: admin/customer/seller Application A UserAuth User New Application B
56. User Single Sign-On UserAuth Auth Engine Application A Example: User User New Application B
57. User Single Sign-On UserAuth Auth Engine Application A Example: User User New Application B
58. User Single Sign-On UserAuth Auth Engine Application A Example: User User New Application B
59. Example: Order … Order status: new / ordered / paid / fulfilled / shipping / finished Order cannot track multiple Shipments Mixing Domains: Process / Payment / Fulfillment / Shipment Changing Order needs re-Payment Order Shipment Shipment Shipment Basket Payment Order Related Order needs another Order 2. Refactoring God Object etc….
61. Is your Software Ready for the Next Build? – Webomates
62. Order status: new / ordered / paid / fulfilled / shipping / finished Shipment Shipment Shipment Order status: new / ordered / paid / fulfilled Track multiple Shipments No need to re-payment Make multiple Orders Order Shipment Shipment Shipment Basket Payment Order Shipment Shipment Shipment Order status: paid / fulfilled Basket Order status: paid / fulfilled 2. Refactoring God Object
63. Example: Order can track multiple Shipments Order status: new / ordered / paid / fulfilled / shipping / finished Shipment Shipment Shipment Order status: new / ordered / paid / fulfilled
64. Strangler Fig Pattern - Martin Fowler The Big Bang | Creating Software - A Sisyphean Task?
65. Refactoring Legacy Code with the Strangler Fig Pattern - Shopify
66. Is the monolith a problem? No The problem is often “God Object” there is a tendency to blame the technology the issue of modeling
67. 1. North star modeling: DRY + DDD To fix “God Object” 2. Refactoring: Incremental release with business merit Feature Flag (Canary release) Shadow Traffic (Parallel adoption) Strangler Fig (Phased implementation)
68. Thank you! Let’s have a chat! https://chikahirotokoro.com/ Chikahiro
69. one more thing…
70. Matz came to my podcast guest! 🤯 (japanese)
71. https://en.kaigaiiju.ch Just released English (AI) translated episodes of Matz! Living Overseas