clientv3: add keep-alive to connection

this makes the grpc client connection use a keep-alive.

clientv3/client.go

@@ -31,6 +31,7 @@ import (
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/keepalive"
 	"google.golang.org/grpc/metadata"
 )
 
@@ -215,6 +216,13 @@ func (c *Client) dialSetupOpts(endpoint string, dopts ...grpc.DialOption) (opts
 	if c.cfg.DialTimeout > 0 {
 		opts = []grpc.DialOption{grpc.WithTimeout(c.cfg.DialTimeout)}
 	}
+	if c.cfg.DialKeepAlive > 0 {
+		opts = append(opts, grpc.DialOption{
+			grpc.WithKeepaliveParams(keepalive.ClientParameters{
+				Time:    c.cfg.DialKeepAlive * time.Second,
+				Timeout: c.cfg.DialKeepAlive * time.Second,
+			})})
+	}
 	opts = append(opts, dopts...)
 
 	f := func(host string, t time.Duration) (net.Conn, error) {

clientv3/config.go

@@ -33,6 +33,10 @@ type Config struct {
 	// DialTimeout is the timeout for failing to establish a connection.
 	DialTimeout time.Duration `json:"dial-timeout"`
 
+	// DialKeepAlive is the time after which client pings the server to see if transport is
+	// alive. It waits for this duration for a response before closing the connection.
+	DialKeepAlive time.Duration `json:"dial-keep-alive"`
+
 	// TLS holds the client secure credentials, if any.
 	TLS *tls.Config