System design interview question
"Design a load balancer. It distributes incoming traffic across a fleet of backend servers, detects unhealthy ones, and must itself be highly available. Millions of connections per second. Tell me which layer you operate at and why."
networking fundamentals plus the balancing algorithms, and — the part most candidates skip — how the load balancer itself is made highly available, since it is by definition in front of everything. The distinguishing content is L4 versus L7, why "least connections" beats round-robin, and health checking that does not cause cascading failure.
On Practick another engineer interviews you live for 60 minutes on a question from this bank. They have the full interviewer guide beside the call: the answers to your clarifying questions, the numbers to hand out, a ladder of follow-ups and a scoring rubric. You get the model solution once the session settles. It is free: interview someone for an hour and you have earned your own.
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