Art of Codeartofcode
Lesson 16 of 17

27. Monolith vs Microservices

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The picture to keep in your head
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27.1 What is a monolith?
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27.2 What are a monolith's strengths?
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27.3 What is a modular monolith?
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27.4 What are microservices?
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27.5 What is the real cost of microservices?
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27.6 How do you draw service boundaries?
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27.7 How does service discovery work?
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27.8 Sync vs async calls between services: when to use which?
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27.9 What does "database per service" mean?
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27.10 When should you split?
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Memory card and where the analogy breaks
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Practice: five levels
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Interview questions
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Solutions
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Sources
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Code lab
27. Monolith vs Microservices

Sources

3 min read+10 XP

Source notes

  • Prime Video: "Scaling up the Prime Video audio/video monitoring service and reducing costs by 90%", Prime Video Tech blog, 2023 (initial design on Step Functions and Lambda hit a scaling limit at about 5% of expected load; moving to a single process on ECS/EC2 cut infrastructure cost by 90%). Checked 2026-10-08.
  • Shopify's modular monolith: Kirsten Westeinde, "Deconstructing the Monolith: Designing Software that Maximizes Developer Productivity", Shopify Engineering, 2019. Checked 2026-10-08.
  • Martin Fowler, "MonolithFirst" (2015) and "StranglerFigApplication" (2004); Martin Fowler and James Lewis, "Microservices" (2014).
  • Conway's law: Melvin E. Conway, "How Do Committees Invent?", Datamation, 1968.
  • Bounded contexts: Eric Evans, Domain-Driven Design (2003).
  • "The Tail at Scale": Jeffrey Dean and Luiz André Barroso, Communications of the ACM, 2013.
  • Team sizes, availabilities, latencies and call counts are illustrative assumptions; arithmetic computed 2026-10-08.
  • Level 3 and Level 4 code: tested 2026-10-08 (code/ch27_services.py, all checks pass).