xDS is a suite of configuration service APIs that allow for dynamic configuration of an Envoy proxy. It's possible to configure Envoy with a few or all of these services. This overview will describe what each service does, and why you would use it.
The Cluster Discovery Service tells Envoy about your clusters. In Envoy’s vernacular, a “cluster” is a named group of host/ports, over which it will load-balance traffic. CDS also allows configuration health checks, and TLS, and other connection types. Cluster instances can be listed statically in CDS or, more commonly, dynamically managed using EDS
Read more about CDS configuration here.
The Endpoint Discovery Service tells Envoy about the instances (endpoints) of your clusters. EDS produces a list of instances for each cluster, and some metadata about each instance.
Read more about EDS configuration here.
The Listener Discovery Service tells Envoy what ports to listen on, and what protocols to terminate on those ports. You can also configure TLS and request logging with this service.
Read more about LDS configuration here.
The Route Discovery Service tells Envoy about the routes for each HTTP Listener configured in the LDS. You can partition the URL-space in to multiple paths, each potentially backed by a different services. You can also add redirects, request and response headers, timeouts, and retry policies.
Read more about RDS configuration here.
For the full xDS configuration reference, read more here.