The control plane is a management layer that applies a consistent set of policies to a distributed data plane. Application network traffic today is frequently managed by data plane proxies such as Envoy Proxy. These data plane proxies are optimized to route and manage traffic based on specific policies. A control plane manages and configures a fleet of data plane proxies to manage traffic appropriately.
The Ambassador API Gateway is an edge control plane built on Envoy Proxy, and translates configuration from Kubernetes Custom Resource Definitions into Envoy configuration to manage North/South (edge) traffic.
Istio is a service mesh built on Envoy Proxy. Similarly, Istio translates Kubernetes Custom Resource Definitions into Envoy configuration for managing East/West traffic.