Documentation: add grpc naming resolver doc

Documentation/dev-guide/grpc_naming.md

@@ -0,0 +1,65 @@
+# gRPC naming and discovery
+
+etcd provides a gRPC resolver to support an alternative name system that fetches endpoints from etcd for discovering gRPC services. The underlying mechanism is based on watching updates to keys prefixed with the service name.
+
+## Using etcd discovery with go-grpc
+
+The etcd client provides a gRPC resolver for resolving gRPC endpoints with an etcd backend. The resolver is initialized with an etcd client and given a target for resolution:
+
+```go
+import (
+	"github.com/coreos/etcd/clientv3"
+	etcdnaming "github.com/coroes/etcd/clientv3/naming"
+
+	"google.golang.org/grpc"
+)
+
+...
+
+cli, cerr := clientv3.NewFromURL("http://localhost:2379")
+r := &etcdnaming.GRPCResolver{Client: cli}
+b := grpc.RoundRobin(r)
+conn, gerr := grpc.Dial("my-service", grpc.WithBalancer(b))
+```
+
+## Managing service endpoints
+
+The etcd resolver treats all keys under the prefix of the resolution target following a "/" (e.g., "my-service/") with JSON-encoded go-grpc `naming.Update` values as potential service endpoints. Endpoints are added to the service by creating new keys and removed from the service by deleting keys.
+
+### Adding an endpoint
+
+New endpoints can be added to the service through `etcdctl`:
+
+```sh
+ETCDCTL_API=3 etcdctl put my-service/1.2.3.4 '{"Addr":"1.2.3.4","Metadata":"..."}'
+```
+
+The etcd client's `GRPCResolver.Update` method can also register new endpoints with a key matching the `Addr`:
+
+```go
+r.Update(context.TODO(), "my-service", naming.Update{Op: naming.Add, Addr: "1.2.3.4", Metadata: "..."})
+```
+
+### Deleting an endpoint
+
+Hosts can be deleted from the service through `etcdctl`:
+
+```sh
+ETCDCTL_API=3 etcdctl del my-service/1.2.3.4
+```
+
+The etcd client's `GRPCResolver.Update` method also supports deleting endpoints:
+
+```go
+r.Update(context.TODO(), "my-service", naming.Update{Op: naming.Delete, Addr: "1.2.3.4"})
+```
+
+### Registering an endpoint with a lease
+
+Registering an endpoint with a lease ensures that if the host can't maintain a keepalive heartbeat (e.g., its machine fails), it will be removed from the service:
+
+```sh
+lease=`ETCDCTL_API=3 etcdctl lease grant 5 | cut -f2 -d' '`
+ETCDCTL_API=3 etcdctl put --lease=$lease my-service/1.2.3.4 '{"Addr":"1.2.3.4","Metadata":"..."}'
+ETCDCTL_API=3 etcdctl lease keep-alive $lease
+```

Documentation/docs.md

@@ -14,6 +14,7 @@ The easiest way to get started using etcd as a distributed key-value store is to
  - [Interacting with etcd][interacting]
  - [API references][api_ref]
  - [gRPC gateway][api_grpc_gateway]
+ - [gRPC naming and discovery][grpc_naming]
  - [Embedding etcd][embed_etcd]
  - [Experimental features and APIs][experimental]
 
@@ -60,6 +61,7 @@ To learn more about the concepts and internals behind etcd, read the following p
 [demo]: demo.md
 [download_build]: dl_build.md
 [embed_etcd]: https://godoc.org/github.com/coreos/etcd/embed
+[grpc_naming]: dev-guide/grpc_naming.md
 [failures]: op-guide/failures.md
 [gateway]: op-guide/gateway.md
 [glossary]: learning/glossary.md