Interview › Istio & Service Mesh
How does Istio support traffic mirroring (shadowing), and why is it useful?
Istio & Service Mesh · Advanced level
Answer
Traffic mirroring, or shadowing, sends a copy of live requests to another destination while the original request still goes to the primary service. It is useful for testing a new version with production-like traffic without affecting user responses.
Technical explanation
Mirrored traffic should not perform real side effects such as charging cards, sending emails, or writing authoritative data unless safely isolated.
The mirrored response is discarded, so it cannot directly affect the user's request.
Mirror percentage and destination must be controlled to avoid overloading the shadow service.
Hands-on example
VirtualService sketch:
route:
- destination:
host: checkout
subset: v1
weight: 100
mirror:
host: checkout
subset: v2
mirrorPercentage:
value: 10
Ensure v2 writes to a shadow database or runs in read-only mode before enabling.
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