How does an Elastic Load Balancer work, and what are ALB vs NLB vs CLB?
AWS · Basic level
Answer
Elastic Load Balancing distributes traffic to healthy targets. ALB is Layer 7 for HTTP/HTTPS routing, NLB is Layer 4 for TCP/UDP/TLS and high performance/static IP needs, and CLB is legacy for older patterns.
Technical explanation
ALB is application-aware; NLB is transport-focused; CLB should generally be treated as legacy.
Compute design should balance availability, scaling speed, startup time, instance limits, health checks, and deployment rollback, not just raw instance size.
Autoscaling and load balancing only work well when health checks reflect readiness and when applications externalize state.
Cost optimization should be tied to utilization data and workload tolerance for interruption, commitment, and architecture changes.
Hands-on example
1. Build a launch template or workload definition with IAM role, security groups, user data/bootstrap, health endpoint, and CloudWatch metrics.
2. Place compute behind an ALB/NLB or scaling group and run a controlled load test to observe scaling and health behavior.
3. Tune scaling policy, warmup/cooldown, target group health checks, and rollback procedure.
4. Compare cost and reliability after the test, then promote the configuration through IaC.
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