Art of Codeartofcode
Lesson 15 of 16

6. Vertical vs Horizontal Scaling

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The picture to keep in your head
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6.1 What does "scaling" actually mean?
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6.2 What is vertical scaling?
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6.3 What is horizontal scaling?
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6.4 Why does scaling out need stateless servers?
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6.5 If servers are stateless, where does the state go?
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6.6 What is autoscaling, and how do you get it right?
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6.7 What about the database? Why is it the hardest part to scale?
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6.8 What does each kind of scaling really cost?
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6.9 So when do you choose which?
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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
6. Vertical vs Horizontal Scaling

Sources

3 min read+10 XP

Source notes

  • Amdahl's law: Gene Amdahl, "Validity of the single processor approach to achieving large scale computing capabilities", AFIPS Conference Proceedings, 1967. Speed-up figures computed 2026-10-08.
  • Autoscaling concepts (target tracking, scheduled and predictive scaling, cooldowns, warm-up) are described in the major cloud providers' autoscaling documentation (for example, AWS EC2 Auto Scaling and Google Cloud managed instance groups). Behaviour details vary by provider.
  • Spot or preemptible instances can be reclaimed by the provider at short notice: provider documentation (AWS Spot Instances, Google Cloud Spot VMs).
  • All Book Fest numbers (traffic, per-server capacity, warm-up time, hours) are illustrative assumptions. Arithmetic computed 2026-10-08.
  • Level 3 and Level 4 code: tested 2026-10-08 (code/ch06_scaling.py, all checks pass).