Feature request: Allow Direct Request Routing to Canary Deployment During Rollout

[lennarkivimae]

Describe the feature

Allow users to explicitly route requests directly to the canary deployment during an active rollout, bypassing the current weight-based distribution. This is particularly beneficial for conducting end-to-end tests against the canary build, enabling early detection of potential issues before full deployment.

Proposed solution

Currently, defining headers automatically initiates A/B testing mode within Flagger. The suggested improvement is to decouple A/B testing from header-based routing by introducing a separate flag. This would allow headers to be utilized exclusively for routing specific traffic directly to the canary deployment.

Any alternatives you've considered?

No viable alternatives were found. As previously mentioned, using headers currently forces Flagger into A/B testing mode. While it is possible to run e2e tests and perform load testing within the existing framework, load tests alone often fail to replicate realistic usage scenarios effectively.