One server can only take so much. When traffic climbs, CPU saturates, response times stretch, and requests start failing — and every user is stuck behind the same bottleneck.
A load balancer sits in front of your backends and spreads incoming requests across them. Instead of one server at 98%, you get several at 40%.
The part that matters more than the distribution: HEALTH CHECKS. The balancer keeps probing each backend, and when one stops answering, it takes that server out of rotation and sends new traffic to the others. Your users see a working site while you fix the broken box.
USERS → LOAD BALANCER → SERVERS
Three honest limits, because this gets oversold:
✘ It won't stop every outage. The balancer itself can fail, your database is still a shared dependency, and losing enough backends still takes you down.
✘ It doesn't make any single response faster. One request to an idle server is the same speed either way — what improves is throughput and what happens under load.
✘ There's no single algorithm. Round robin, least connections, IP hash, weighted variants — what you get depends on the product and how it's configured.
NGINX and the cloud providers' load balancers both do this job, but they are not drop-in equivalents. Health check semantics, TLS termination, protocol support and failover behaviour all differ. Read the docs for the one you're actually running.
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