What Is a Load Balancer?
a Load Balancer — a device or service that spreads incoming requests across multiple servers so no single one is overwhelmed — the backbone of every large website's availability.
How it works
Clients hit one virtual address; the balancer forwards each request to a healthy backend chosen by algorithm (round-robin, least connections). Health checks pull dead servers out automatically. Layer 4 balancers work on IP/port; Layer 7 balancers read HTTP and can route by URL or cookie.
Why it matters
Load balancing links networking to cloud: AWS/Azure balancers are among the first services engineers meet, and the concept (plus health checks and session persistence) shows up in CCNP design and cloud interviews alike.
Frequently asked questions
Why use a load balancer?
To scale beyond one server and to survive server failures — traffic automatically shifts to healthy machines.
What is the difference between Layer 4 and Layer 7 load balancing?
L4 balances on addresses/ports without reading content; L7 understands HTTP and can route on URLs, headers or cookies.
What is a health check?
A periodic probe the balancer sends each backend; failures remove that server from rotation until it recovers.
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