Galley is the top-level config ingestion, processing and distribution component of Istio. It is responsible for insulating the rest of the Istio components from the details of obtaining user configuration from the underlying platform. It contains Kubernetes CRD listeners for collecting configuration, an MCP protocol server implementation for distributing config, and a validation web-hook for pre-ingestion validation by Kubernetes API Server.
High-level design doc (Oct 2019)