Mixer is a general-purpose policy and telemetry hub. It enforces access control and usage policies across the service mesh. Mixer includes a flexible plugin model that can abstract the Envoy proxy and Istio-managed services. This model allows Istio to interface with a variety of infrastructure backends. 

Mixer is a platform-independent component of Istio that runs in Kubernetes or other environments.

The base model of Mixer allows it to connect to a variety of access control systems for authorization, telemetry capturing, quota enforcement, logging backend, and more. This can be seen in the following diagram:

Mixer is a framework that can be seamlessly integrated with infrastructure layers to give control to operations and remove policy logic from the control plane.

The sidecar proxy function is used to call Mixer before each request to perform condition checks. This is also done after each request to report on telemetry data. This introduces Mixer as a single point of the bottleneck, and this is avoided by the proxy to keep a cache of precondition checks and to buffer telemetry data in order to avoid each hop to the Mixer.

The policy enforcement and telemetry collections are configuration-driven, which means Mixer gives us control of the operations. Mixer insulates the Istio control plane from the implementation details of individual backends.