Initial checkin of gRPC to third_party/

third_party/grpc/doc/naming.md

+#gRPC Naming and Discovery Support
+
+## Overview
+
+gRPC supports DNS as the default name-system. A number of alternative name-systems are used in various deployments. We propose an API that is general enough to support a range of name-systems and the corresponding syntax for names. The gRPC client library in various languages will provide a plugin mechanism so resolvers for different name-systems can be plugged in.
+
+## Detailed Proposal
+
+ A fully qualified, self contained name used for gRPC channel construction uses the syntax:
+
+```
+scheme://authority/endpoint_name
+```
+
+Here, scheme indicates the name-system to be used. Example schemes to be supported include: 
+
+* `dns`
+
+* `zookeeper`
+
+* `etcd`
+
+Authority indicates some scheme-specific bootstrap information, e.g., for DNS, the authority may include the IP[:port] of the DNS server to use. Often, a DNS name may used as the authority, since the ability to resolve DNS names is already built into all gRPC client libraries.
+
+Finally, the  endpoint_name indicates a concrete name to be looked up in a given name-system identified by the scheme and the authority. The syntax of endpoint name is dictated by the scheme in use.
+
+### Plugins
+
+The gRPC client library will switch on the scheme to pick the right resolver plugin and pass it the fully qualified name string.
+
+Resolvers should be able to contact the authority and get a resolution that they return back to the gRPC client library. The returned contents include a list of IP:port, an optional config and optional auth config data to be used for channel authentication. The plugin API allows the resolvers to continuously watch an endpoint_name and return updated resolutions as needed. 
+
+## Zookeeper
+
+Apache [ZooKeeper](https://zookeeper.apache.org/) is a popular solution for building name-systems. Curator is a service discovery system built on to of ZooKeeper. We propose to organize names hierarchically as `/path/service/instance` similar to Apache Curator.
+
+A fully-qualified ZooKeeper name used to construct a gRPC channel will look as follows:
+
+```
+zookeeper://host:port/path/service/instance
+```
+Here `zookeeper` is the scheme identifying the name-system. `host:port` identifies an authoritative name-server for this scheme (i.e., a  Zookeeper server). The host can be an IP address or a DNS name. 
+Finally `/path/service/instance` is the Zookeeper name to be resolved. 
+
+## Service Registration
+
+
+Service providers can register their services in Zookeeper by using a Zookeeper client.  
+
+Each service is a zookeeper node, and each instance is a child node of the corresponding service. For example, a MySQL service may have multiple instances, `/mysql/1`, `/mysql/2`, `/mysql/3`. The name of the service or instance, as well as an optional path is specified by the service provider.
+
+The data in service nodes is empty. Each instance node stores its address in the format of `host:port`, where host can be either hostname or IP address.