Software → System Design
Horizontal Scaling
Increasing capacity by adding more machines, instances, or nodes.
Where it fits
Horizontal scaling increases capacity by adding more instances or nodes. It is a core system design and operations idea.
Mental model
Instead of making one machine bigger, you add more machines and distribute work across them.
Example
A service running on two servers can scale to ten servers behind a load balancer during high traffic.
Common mistakes
- Horizontally scaling stateful services without handling shared state.
- Forgetting load balancing, data partitioning, and coordination.
- Assuming all workloads scale linearly.
Related concepts
Load balancer, stateless, database sharding, autoscaling, elasticity.