Update federation target to etcd/clientv3 (#6119)

With CoreDNS now supporting etcdv3 as the DNS backend, we
can update our federation target to etcdv3. Users will now be
able to use etcdv3 server as the federation backbone.

Minio will update bucket data to etcdv3 and CoreDNS can pick
that data up and serve it as bucket style DNS path.

cmd/common-main.go

@@ -26,7 +26,7 @@ import (
 	"strings"
 	"time"
 
-	etcd "github.com/coreos/etcd/client"
+	etcd "github.com/coreos/etcd/clientv3"
 
 	"github.com/minio/cli"
 	"github.com/minio/minio/cmd/logger"
@@ -51,17 +51,19 @@ func checkUpdate(mode string) {
 // Initialize and load config from remote etcd or local config directory
 func initConfig() {
 	if globalEtcdClient != nil {
-		kapi := etcd.NewKeysAPI(globalEtcdClient)
 		ctx, cancel := context.WithTimeout(context.Background(), 20*time.Second)
-		_, err := kapi.Get(ctx, getConfigFile(), nil)
+		resp, err := globalEtcdClient.Get(ctx, getConfigFile())
 		cancel()
-		if err == nil {
-			logger.FatalIf(migrateConfig(), "Config migration failed.")
-			logger.FatalIf(loadConfig(), "Unable to load config version: '%s'.", serverConfigVersion)
+		// This means there are no entries in etcd with config file
+		// So create a new config
+		if err == nil && resp.Count == 0 {
+			logger.FatalIf(newConfig(), "Unable to initialize minio config for the first time.")
+			logger.Info("Created minio configuration file successfully at %v", globalEtcdClient.Endpoints())
 		} else {
-			if etcd.IsKeyNotFound(err) {
-				logger.FatalIf(newConfig(), "Unable to initialize minio config for the first time.")
-				logger.Info("Created minio configuration file successfully at %v", globalEtcdClient.Endpoints())
+			// This means there is an entry in etcd, update it if required and proceed
+			if err == nil && resp.Count > 0 {
+				logger.FatalIf(migrateConfig(), "Config migration failed.")
+				logger.FatalIf(loadConfig(), "Unable to load config version: '%s'.", serverConfigVersion)
 			} else {
 				logger.FatalIf(err, "Unable to load config version: '%s'.", serverConfigVersion)
 			}
@@ -155,8 +157,9 @@ func handleCommonEnvVars() {
 		etcdEndpoints := strings.Split(etcdEndpointsEnv, ",")
 		var err error
 		globalEtcdClient, err = etcd.New(etcd.Config{
-			Endpoints: etcdEndpoints,
-			Transport: NewCustomHTTPTransport(),
+			Endpoints:         etcdEndpoints,
+			DialTimeout:       defaultDialTimeout,
+			DialKeepAliveTime: defaultDialKeepAlive,
 		})
 		logger.FatalIf(err, "Unable to initialize etcd with %s", etcdEndpoints)
 	}