Horizontal Scaling: What Changes When You Add More Servers

“Learn stateless services, shared state and the hidden complexity of scaling out.”

Horizontal Scaling

Vertical scaling gives one machine more CPU, RAM or storage.

Horizontal scaling adds more machines.

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If a session exists only inside Application 1, a request reaching Application 2 may not know about it.

Possible solutions include signed tokens, Redis-backed sessions or database-backed sessions.

Shared object storage is usually a better fit than ephemeral local disks.

2 servers × 20 connections = 40
20 servers × 20 connections = 400

Connection pooling becomes important.

Note

Scaling one layer can simply move the bottleneck to another layer.

Always ask what happens if two different machines execute the same code at the same time.

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