The correct option is Istiod.

Istiod is the Istio control plane component that manages configuration distribution and service discovery for Envoy sidecars. It programs Envoy proxies with routing rules and traffic shifting so you can steer traffic between service revisions during canary deployments.

Traffic Director is a Google Cloud managed service for controlling proxy based traffic in GCP environments but it is not part of the Istio control plane and it does not perform Istio specific routing for canaries.

Istio Mixer was the policy and telemetry component in older Istio releases but it did not program Envoy routing and it has been deprecated and removed in recent Istio versions. That is why it is not responsible for steering traffic on modern Istio installations.

Istio Citadel provided certificate authority and workload identity functions for mTLS. Its responsibilities were merged into Istiod and it did not handle routing rules, so it is not used to steer traffic during canary deployments.

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