vendor update for CSI 0.3.0

vendor/google.golang.org/grpc/Documentation/stickiness.md

@@ -0,0 +1,46 @@
+# Stickiness
+
+With load balancer, each RPC pick a different backend based on the load
+balancing policy. Stickiness policies try to preserve peers for the duration of
+a session, so that RPCs with the same stickiness key will be directed to the
+same server.
+
+Note that there's only "soft" stickiness now, which means RPCs with the same
+stickienss key could still be sent to different servers. If stickiness is
+critical for the system, server side application level handling is still
+necessary.
+
+## Stickiness Key
+
+A stickiness key works as the session id. RPCs with the same stickiness key will
+be assigned to the same backend.
+
+Stickiness key is set as part of the custom metadata.
+
+## Enable stickiness
+
+Stickiness can be enabled by setting `stickinessKey` field in [service
+config](https://github.com/grpc/grpc/blob/master/doc/service_config.md).
+
+```json
+{
+  "stickinessKey": "sessionid"
+}
+```
+
+The value `sesseionid` will be used as the key of the metadata entry that
+defines the stickiness key for each RPC.
+
+## Send RPC with stickiness
+
+To set the stickiness key for an RPC, set the corresponding metadata. The
+following RPC will be sent with stickiness key `session1`.
+
+```go
+// "sessionid" is the metadata key specified by service config, "session1" is
+// the stickiness key for this RPC.
+md := metadata.Paris("sessionid", "session1")
+
+ctx := metadata.NewOutgoingContext(context.Background(), md)
+resp, err := client.SomeRPC(ctx, req)
+```