Glossary · Reliability & operations
Shadow Traffic
A copy of live request traffic sent to a candidate system for observation while the candidate response remains outside the primary user response path. Because the copied request still executes, its side effects must be isolated.
Why it matters
It exposes the candidate to real input shapes and load while limiting user impact, which can reveal failures absent from synthetic tests.
In practice
Remove or tokenize sensitive fields, route tools and dependencies to sandboxed or no-op targets, block writes at capability boundaries, preserve request correlation, and prevent shadow load from competing with user traffic.
Common confusion
Keeping a candidate response off the primary path does not make execution side-effect-free. A canary release differs because it serves real users from the candidate for a controlled share of traffic.
Related terms
Sources
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