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⚖️ How Load Balancers Work

Learn how load balancers distribute traffic, route by transport or application signals, remove unhealthy servers, and support reliable change.

4
lessons
~10 min
to learn
Adults
level
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What you’ll learn

  1. The Traffic ProblemExplain why several backend servers can share one public service address.A load balancer distributes arrivals across a pool while the application and its shared state still need their own design.
  2. Choosing a TargetDistinguish transport- and application-aware routing, then compare common target-selection algorithms.Layer 4 and Layer 7 make different information available; round robin is predictable, while weighted and least-load approaches adapt to capacity or current work.
  3. Health and FailureDescribe health checks, draining, and safe backend removal.Health signals control eligibility, and draining protects in-flight work during maintenance or scaling.
  4. Availability and Trade-offsConnect load-balancer scope, redundancy, state, and observability to reliable service.Regional and global routing add layers; resilient designs monitor the full path and match routing to protocol and state.

Questions this course answers

Which capability is most characteristic of Layer 7 load balancing?

Layer 7 balancers understand application information such as HTTP paths, hosts, headers, or cookies and can use it in routing rules.

Match each mechanism to its main job.

These mechanisms solve different problems: eligibility, distribution, and graceful change.

Why can a global DNS failover decision take time to reach every user?

Cached DNS answers can remain in use until their TTL or local policy allows another lookup, so DNS steering is not always immediate.

Grounded in trusted sources

  • https://docs.aws.amazon.com/elasticloadbalancing/latest/userguide/how-elastic-load-balancing-works.html
  • https://docs.aws.amazon.com/elasticloadbalancing/latest/application/introduction.html
  • https://learn.microsoft.com/en-us/azure/architecture/guide/technology-choices/load-balancing-overview
  • https://learn.microsoft.com/en-us/azure/load-balancer/concepts
  • https://nginx.org/en/docs/http/load_balancing.html
  • https://developers.cloudflare.com/load-balancing/understand-basics/

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