Lock: Use REST API instead of RPC (#7469)

In distributed mode, use REST API to acquire and manage locks instead
of RPC.

RPC has been completely removed from MinIO source.

Since we are moving from RPC to REST, we cannot use rolling upgrades as the
nodes that have not yet been upgraded cannot talk to the ones that have
been upgraded.

We expect all minio processes on all nodes to be stopped and then the
upgrade process to be completed.

Also force http1.1 for inter-node communication

cmd/namespace-lock.go

@@ -38,7 +38,7 @@ import (
 var globalNSMutex *nsLockMap
 
 // Global lock server one per server.
-var globalLockServer *lockRPCReceiver
+var globalLockServer *lockRESTServer
 
 // Instance of dsync for distributed clients.
 var globalDsync *dsync.Dsync
@@ -66,7 +66,7 @@ func newDsyncNodes(endpoints EndpointList) (clnts []dsync.NetLocker, myNode int)
 		if endpoint.IsLocal {
 			myNode = len(clnts)
 
-			receiver := &lockRPCReceiver{
+			receiver := &lockRESTServer{
 				ll: localLocker{
 					serverAddr:      endpoint.Host,
 					serviceEndpoint: lockServicePath,
@@ -79,8 +79,7 @@ func newDsyncNodes(endpoints EndpointList) (clnts []dsync.NetLocker, myNode int)
 		} else {
 			host, err := xnet.ParseHost(endpoint.Host)
 			logger.FatalIf(err, "Unable to parse Lock RPC Host")
-			locker, err = NewLockRPCClient(host)
-			logger.FatalIf(err, "Unable to initialize Lock RPC Client")
+			locker = newlockRESTClient(host)
 		}
 
 		clnts = append(clnts, locker)