Callout-based Service Extensions let you use Cloud Load Balancing to make gRPC calls to user-managed services during data processing. You write callout extensions against Envoy's external processing gRPC API. Callout extensions run as general-purpose gRPC servers on user-managed compute VMs and Google Kubernetes Engine Pods on Google Cloud, multicloud, or on-premises environments. This directory contains Python SDKs that will simplify your extension development. SDKs for other languages are coming soon.