diff --git a/infra/conf/http.go b/infra/conf/http.go
index 84155d54..63294ca1 100644
--- a/infra/conf/http.go
+++ b/infra/conf/http.go
@@ -64,25 +64,24 @@ type HTTPClientConfig struct {
 func (v *HTTPClientConfig) Build() (proto.Message, error) {
 	config := new(http.ClientConfig)
 	if v.Address != nil {
-		if len(v.Username) == 0 {
-			v.Servers = []*HTTPRemoteConfig{
-				{
-					Address: v.Address,
-					Port:    v.Port,
-				},
-			}
-		} else {
-			v.Servers = []*HTTPRemoteConfig{
-				{
-					Address: v.Address,
-					Port:    v.Port,
-					Users:   []json.RawMessage{{}},
-				},
-			}
+		v.Servers = []*HTTPRemoteConfig{
+			{
+				Address: v.Address,
+				Port:    v.Port,
+			},
 		}
+		if len(v.Username) > 0 {
+			v.Servers[0].Users = []json.RawMessage{{}}
+		}
+	}
+	if len(v.Servers) != 1 {
+		return nil, errors.New(`HTTP settings: "servers" should have one and only one member. Multiple endpoints in "servers" should use multiple HTTP outbounds and routing balancer instead`)
 	}
 	config.Server = make([]*protocol.ServerEndpoint, len(v.Servers))
 	for idx, serverConfig := range v.Servers {
+		if len(serverConfig.Users) > 1 {
+			return nil, errors.New(`HTTP servers: "users" should have one member at most. Multiple members in "users" should use multiple HTTP outbounds and routing balancer instead`)
+		}
 		server := &protocol.ServerEndpoint{
 			Address: serverConfig.Address.Build(),
 			Port:    uint32(serverConfig.Port),
diff --git a/infra/conf/shadowsocks.go b/infra/conf/shadowsocks.go
index a05c1dc5..04e60bd0 100644
--- a/infra/conf/shadowsocks.go
+++ b/infra/conf/shadowsocks.go
@@ -172,16 +172,16 @@ type ShadowsocksServerTarget struct {
 }
 
 type ShadowsocksClientConfig struct {
-	Address    *Address `json:"address"`
-	Port       uint16   `json:"port"`
-	Level      byte     `json:"level"`
-	Email      string   `json:"email"`
-	Cipher     string   `json:"method"`
-	Password   string   `json:"password"`
-	IVCheck    bool     `json:"ivCheck"`
-	UoT        bool     `json:"uot"`
-	UoTVersion int      `json:"uotVersion"`
-	Servers []*ShadowsocksServerTarget `json:"servers"`
+	Address    *Address                   `json:"address"`
+	Port       uint16                     `json:"port"`
+	Level      byte                       `json:"level"`
+	Email      string                     `json:"email"`
+	Cipher     string                     `json:"method"`
+	Password   string                     `json:"password"`
+	IVCheck    bool                       `json:"ivCheck"`
+	UoT        bool                       `json:"uot"`
+	UoTVersion int                        `json:"uotVersion"`
+	Servers    []*ShadowsocksServerTarget `json:"servers"`
 }
 
 func (v *ShadowsocksClientConfig) Build() (proto.Message, error) {
@@ -200,8 +200,8 @@ func (v *ShadowsocksClientConfig) Build() (proto.Message, error) {
 			},
 		}
 	}
-	if len(v.Servers) == 0 {
-		return nil, errors.New("0 Shadowsocks server configured.")
+	if len(v.Servers) != 1 {
+		return nil, errors.New(`Shadowsocks settings: "servers" should have one and only one member. Multiple endpoints in "servers" should use multiple Shadowsocks outbounds and routing balancer instead`)
 	}
 
 	if len(v.Servers) == 1 {
diff --git a/infra/conf/socks.go b/infra/conf/socks.go
index 1d7c6249..fa5d2bf3 100644
--- a/infra/conf/socks.go
+++ b/infra/conf/socks.go
@@ -82,25 +82,24 @@ type SocksClientConfig struct {
 func (v *SocksClientConfig) Build() (proto.Message, error) {
 	config := new(socks.ClientConfig)
 	if v.Address != nil {
-		if len(v.Username) == 0 {
-			v.Servers = []*SocksRemoteConfig{
-				{
-					Address: v.Address,
-					Port:    v.Port,
-				},
-			}
-		} else {
-			v.Servers = []*SocksRemoteConfig{
-				{
-					Address: v.Address,
-					Port:    v.Port,
-					Users:   []json.RawMessage{{}},
-				},
-			}
+		v.Servers = []*SocksRemoteConfig{
+			{
+				Address: v.Address,
+				Port:    v.Port,
+			},
 		}
+		if len(v.Username) > 0 {
+			v.Servers[0].Users = []json.RawMessage{{}}
+		}
+	}
+	if len(v.Servers) != 1 {
+		return nil, errors.New(`SOCKS settings: "servers" should have one and only one member. Multiple endpoints in "servers" should use multiple SOCKS outbounds and routing balancer instead`)
 	}
 	config.Server = make([]*protocol.ServerEndpoint, len(v.Servers))
 	for idx, serverConfig := range v.Servers {
+		if len(serverConfig.Users) > 1 {
+			return nil, errors.New(`SOCKS servers: "users" should have one member at most. Multiple members in "users" should use multiple SOCKS outbounds and routing balancer instead`)
+		}
 		server := &protocol.ServerEndpoint{
 			Address: serverConfig.Address.Build(),
 			Port:    uint32(serverConfig.Port),
diff --git a/infra/conf/trojan.go b/infra/conf/trojan.go
index d7d4ea17..b495bab4 100644
--- a/infra/conf/trojan.go
+++ b/infra/conf/trojan.go
@@ -28,13 +28,13 @@ type TrojanServerTarget struct {
 
 // TrojanClientConfig is configuration of trojan servers
 type TrojanClientConfig struct {
-	Address  *Address `json:"address"`
-	Port     uint16   `json:"port"`
-	Level    byte     `json:"level"`
-	Email    string   `json:"email"`
-	Password string   `json:"password"`
-	Flow     string   `json:"flow"`
-	Servers []*TrojanServerTarget `json:"servers"`
+	Address  *Address              `json:"address"`
+	Port     uint16                `json:"port"`
+	Level    byte                  `json:"level"`
+	Email    string                `json:"email"`
+	Password string                `json:"password"`
+	Flow     string                `json:"flow"`
+	Servers  []*TrojanServerTarget `json:"servers"`
 }
 
 // Build implements Buildable
@@ -51,8 +51,8 @@ func (c *TrojanClientConfig) Build() (proto.Message, error) {
 			},
 		}
 	}
-	if len(c.Servers) == 0 {
-		return nil, errors.New("0 Trojan server configured.")
+	if len(c.Servers) != 1 {
+		return nil, errors.New(`Trojan settings: "servers" should have one and only one member. Multiple endpoints in "servers" should use multiple Trojan outbounds and routing balancer instead`)
 	}
 
 	config := &trojan.ClientConfig{
diff --git a/infra/conf/vless.go b/infra/conf/vless.go
index aa410e5c..b45b9057 100644
--- a/infra/conf/vless.go
+++ b/infra/conf/vless.go
@@ -228,7 +228,7 @@ func (c *VLessOutboundConfig) Build() (proto.Message, error) {
 		}
 	}
 	if len(c.Vnext) != 1 {
-		return nil, errors.New(`VLESS settings: "vnext" should have one and only one member`)
+		return nil, errors.New(`VLESS settings: "vnext" should have one and only one member. Multiple endpoints in "vnext" should use multiple VLESS outbounds and routing balancer instead`)
 	}
 	config.Vnext = make([]*protocol.ServerEndpoint, len(c.Vnext))
 	for idx, rec := range c.Vnext {
@@ -236,7 +236,7 @@ func (c *VLessOutboundConfig) Build() (proto.Message, error) {
 			return nil, errors.New(`VLESS vnext: "address" is not set`)
 		}
 		if len(rec.Users) != 1 {
-			return nil, errors.New(`VLESS vnext: "users" should have one and only one member`)
+			return nil, errors.New(`VLESS vnext: "users" should have one and only one member. Multiple members in "users" should use multiple VLESS outbounds and routing balancer instead`)
 		}
 		spec := &protocol.ServerEndpoint{
 			Address: rec.Address.Build(),
diff --git a/infra/conf/vmess.go b/infra/conf/vmess.go
index c0171c4b..71eafaa2 100644
--- a/infra/conf/vmess.go
+++ b/infra/conf/vmess.go
@@ -139,16 +139,16 @@ func (c *VMessOutboundConfig) Build() (proto.Message, error) {
 			},
 		}
 	}
-	if len(c.Receivers) == 0 {
-		return nil, errors.New("0 VMess receiver configured")
+	if len(c.Receivers) != 1 {
+		return nil, errors.New(`VMess settings: "vnext" should have one and only one member. Multiple endpoints in "vnext" should use multiple VMess outbounds and routing balancer instead`)
 	}
 	serverSpecs := make([]*protocol.ServerEndpoint, len(c.Receivers))
 	for idx, rec := range c.Receivers {
-		if len(rec.Users) == 0 {
-			return nil, errors.New("0 user configured for VMess outbound")
+		if len(rec.Users) != 1 {
+			return nil, errors.New(`VMess vnext: "users" should have one and only one member. Multiple members in "users" should use multiple VMess outbounds and routing balancer instead`)
 		}
 		if rec.Address == nil {
-			return nil, errors.New("address is not set in VMess outbound config")
+			return nil, errors.New(`VMess vnext: "address" is not set`)
 		}
 		spec := &protocol.ServerEndpoint{
 			Address: rec.Address.Build(),