How does a load balancer distribute traffic, and what algorithms are common?
Reviewed by Gurusankar M.
⚡ Short Answer
A load balancer spreads requests across healthy backends and removes failed ones via health checks. Common algorithms: round-robin, least-connections, and consistent-hashing (sticky by key). L4 balances by TCP/IP (fast), L7 by HTTP content (path/host routing).
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“How does a load balancer distribute traffic, and what algorithms are common?”
🧠Mind Map Answer
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🔥What If?
Think Beyond the Expected
Why are health checks essential to a load balancer?
Without them the LB keeps sending traffic to dead/unhealthy instances, so users get errors. Health checks let the LB detect failures and route only to healthy targets — the core of self-healing and zero-downtime deploys.
😂Real World
L7 load balancers (ALB/Nginx) do path/host routing and TLS termination; least-connections suits uneven request costs. Health checks + connection draining make deploys and failures invisible to users.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗No/weak health checks
- ✗Sticky sessions defeating even distribution
- ✗Single LB as a SPOF
✅Best Practices
- ✓Health checks + connection draining
- ✓Pick the algorithm to match request cost
- ✓Run the LB redundantly
🔁Follow-up Questions
- 1When do you need sticky sessions (and why avoid them)?
- 2L4 vs L7 — trade-offs?
- 3How does the LB itself avoid being a SPOF?
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Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: Load Balancing (System Design) Interview question: "How does a load balancer distribute traffic, and what algorithms are common?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
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