Terminology

Host: An entity capable of network communication (application on a mobile phone, server, etc.). In this documentation a host is a logical network application. A physical piece of hardware could possibly have multiple hosts running on it as long as each of them can be independently addressed.

Upstream: An upstream host receives connections and requests from Envoy and returns responses.

Cluster: A cluster is a group of logically similar upstream hosts that Envoy connects to. Envoy discovers the members of a cluster via service discovery. It optionally determines the health of cluster members via . The cluster member that Envoy routes a request to is determined by the load balancing policy.

Runtime configuration: Out of band realtime configuration system deployed alongside Envoy. Configuration settings can be altered that will affect operation without needing to restart Envoy or change the primary configuration.