A team wants to shift 5% of production traffic to a new Lambda version while keeping instant rollback, all without changing client code. Which feature enables this?
A.Environment variable flag
An env flag can't split invocations across deployed versions.
B.Lambda alias with weighted routing between versions
Correct. Weighted aliases are Lambda's native traffic-shifting feature.
C.Two separate function names with client-side load balancing
Duplicating functions pushes orchestration to clients — wrong layer.
D.Lambda layers
Layers share code libraries; they don't route traffic.
Why this answer
Lambda versions are immutable snapshots; aliases are named pointers that can split traffic between two versions by weight (e.g., 95%/5%) — the built-in canary mechanism. Rollback is repointing the alias.
Correct answer: B · Last reviewed 2026-10-26
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