In support of https://github.com/envoyproxy/envoy/issues/2200 and some
Google internal needs, we are planning on adding support to Envoy to
allow a configuration (or possibly build) driven decision on whether to
using the existing Envoy in-built Grpc::AsyncClient or
the Google C++ gRPC client library (https://grpc.io/grpc/cpp/index.html).
To move in this direction, the idea is we have the xDS ApiConfigSources,
rate limit service config and other filter configurations point at a
GrpcService object. This can be configured to use an Envoy cluster,
where Grpc::AsyncClient will orchestrate communication, or to contain
the config needed to establish a channel in Google C++ gRPC client
library.
Signed-off-by: Harvey Tuch <htuch@google.com>