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Canary deployments: validating CORS headers before full rollouts
Shift a small percentage of traffic to new builds and compare preflight success rates and header parity.
1 min read
deploymentcorstesting
What to measure
Track OPTIONS success ratio, not just GET/POST, because middleware ordering bugs often surface only on preflight.
Diff Allow-Origin, Allow-Headers, and Max-Age between canary and baseline using scripted probes.
Rollback criteria
Define automatic rollback if CORS denials spike beyond a threshold for any monitored partner origin.
Keep feature flags for risky header changes separate from unrelated application logic.