Understand the load balancer’s role
See how a shared entry point distributes requests across healthy backends.
- Describe the client, load balancer, backend pool, and health-check relationship.
A load balancer accepts traffic at a shared address and chooses a backend from a pool. It can spread work, stop sending new requests to unhealthy instances, and provide a stable entry point while backends change. It does not make an overloaded backend faster, and it can become a bottleneck or failure point unless its own capacity and availability are planned.
In production, a load balancer may be a managed service, a proxy process, or functionality built into a platform.
Practice: lose a backend
Try it
Up to 15 XPWhat happens when app-b dies?
Halfway through this run, app-b stops responding. Look at how many requests fail, then turn on health checks.
Why doesn’t the number drop to zero? Think about what was already happening when it died, and how long noticing takes.
Three equal backends share steady traffic, and app-b fails halfway through.
- app-abusiest: 3 of 8, handled 40
- app-bbusiest: 3 of 8, handled 20
- app-cbusiest: 3 of 8, handled 40
The bar is the busiest moment. The line marks what the backend can handle.
Try it
Up to 15 XPCan a load balancer fix this?
A balancer solves distribution problems. Decide which of these it can actually help with.
“One server is overloaded while two sit idle.”
“You need to replace servers without changing the address clients use.”
“Every server is at full capacity.”
“A slow database query is making every request slow.”
“A crashed server keeps receiving requests.”
Key takeaways
A balancer routes work among a backend pool.
Health checks guide routing but are imperfect signals.
Plan capacity and redundancy for the balancer itself.
Lesson quiz
5 questions · pass with 4 correct · up to 50 XP
Passing this quiz completes the lesson and keeps your streak going. Questions you miss come back in review sessions later.
Questions about this lesson
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