fix: Use dynamic filer address function to eliminate race condition

Instead of using a goroutine to wait for filer discovery before setting
the filer address function, we now set a dynamic function immediately
that returns the current filer address whenever it's called.

This eliminates the race condition where users could create users before
the goroutine completed, and provides clearer error messages when no
filer is available.

The dynamic function is HA-aware - it automatically returns whatever
filer is currently available, adapting to filer failovers.

weed/admin/dash/admin_server.go

@@ -101,36 +101,18 @@ func NewAdminServer(masters string, templateFS http.FileSystem, dataDir string)
 		server.credentialManager = credentialManager
 		glog.V(0).Infof("Credential manager initialized with store type: %s", credentialManager.GetStore().GetName())
 
-		// For stores that need filer address function, set them
+		// For stores that need filer address function, configure them
 		if store := credentialManager.GetStore(); store != nil {
 			if filerFuncSetter, ok := store.(interface {
 				SetFilerAddressFunc(func() pb.ServerAddress, grpc.DialOption)
 			}); ok {
-				glog.V(0).Infof("Credential store supports filer address function, starting discovery goroutine")
-				// Set up a goroutine to configure filer address function once we discover filers
-				// Use aggressive initial retries with exponential backoff for faster startup
-				go func() {
-					retryInterval := 200 * time.Millisecond // Start with fast retries
-					maxInterval := 5 * time.Second
-					for {
-						filerAddr := server.GetFilerAddress()
-						if filerAddr != "" {
-							// Configure the function to dynamically return the current active filer (HA-aware)
-							filerFuncSetter.SetFilerAddressFunc(func() pb.ServerAddress {
-								return pb.ServerAddress(server.GetFilerAddress())
-							}, server.grpcDialOption)
-							glog.V(0).Infof("Credential manager configured with filer: %s", filerAddr)
-							break
-						}
-						glog.V(0).Infof("Waiting for filer discovery for credential manager (retry in %v)...", retryInterval)
-						time.Sleep(retryInterval)
-						// Exponential backoff up to maxInterval
-						retryInterval = retryInterval * 2
-						if retryInterval > maxInterval {
-							retryInterval = maxInterval
-						}
-					}
-				}()
+				// Configure the filer address function to dynamically return the current active filer
+				// This function will be called each time credentials need to be loaded/saved,
+				// so it will automatically use whatever filer is currently available (HA-aware)
+				filerFuncSetter.SetFilerAddressFunc(func() pb.ServerAddress {
+					return pb.ServerAddress(server.GetFilerAddress())
+				}, server.grpcDialOption)
+				glog.V(0).Infof("Credential store configured with dynamic filer address function")
 			} else {
 				glog.V(0).Infof("Credential store %s does not support filer address function", store.GetName())
 			}