Pilot is the core traffic management component of Istio's control plane for the Envoy sidecars. It pushes communication-based policies to sidecar proxies at runtime to enforce traffic management configurations for intelligent routing, such as Canary deployments, blue/green testing, and resiliency features such as timeouts, retries, and circuit breakers. These are all topics that we will look at in more detail later in this chapter.

The following diagram shows the Pilot architecture:

As we can see, Pilot maintains an abstract model of all of the services in the mesh that have been discovered through either Kubernetes or external services through Galley. The platform-specific adapters, such as Kubernetes, Mesos, Cloud Foundry, and so on, are used to populate the abstract model with the service registry and resource information. Kubernetes keeps the service discovery metadata in the etcd database when we create Kubernetes services.

The etcd database is updated when the endpoints are updated when a pod becomes healthy. The traffic management policies that are defined using Istio provide Kubernetes Custom Resource Definitions (CRD) and are pushed down to the Envoy sidecar for implementation.