## Sidecar Mode Implementation Details

Istio CNI injection is currently based on the same Pod annotations used in init-container/inject mode.

### Selection API

- plugin config "exclude namespaces" applies first
- ambient is enabled if:
    - namespace label "istio.io/dataplane-mode" == "ambient", and/or pod label "istio.io/dataplane-mode" == "ambient"

- [PodDisruptionBudget](https://kubernetes.io/docs/concepts/workloads/pods/disruptions/#how-disruption-budgets-work)
- [pod annotations](https://kubernetes.io/docs/concepts/overview/working-with-objects/annotations/)
- [container environment variables](https://kubernetes.io/docs/tasks/inject-data-application/define-environment-variable-container/)
- [ImagePullPolicy](https://kubernetes.io/docs/concepts/containers/images/)

workloads can talk with each other and obey the Istio configuration resources, but each environment
can use different Istio versions and different configuration defaults.

`istioctl kube-inject` or the automatic sidecar injector are used to select the environment.
In the case of the sidecar injector, the namespace label `istio-env: <NAME_OF_ENV>` is used instead