diff --git a/config/outline.go b/config/outline.go
index 5639b10..b314924 100644
--- a/config/outline.go
+++ b/config/outline.go
@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"golang.org/x/crypto/ssh"
 	"io/ioutil"
-	"log"
 	"net"
 	"net/http"
 	"strconv"
@@ -23,7 +22,46 @@ type Outline struct {
 	SSHPassword   string `json:"sshPassword"`
 }
 
+func (outline Outline) getConfig() ([]byte, error) {
+	if outline.Server == "" {
+		return nil, fmt.Errorf("server field cannot be empty")
+	}
+	tryList := []func() ([]byte, error){
+		outline.getConfigFromLink,
+		outline.getConfigFromSSH,
+	}
+	var (
+		err  error
+		errs []error
+		b    []byte
+	)
+	for _, f := range tryList {
+		b, err = f()
+		if err != nil {
+			errs = append(errs, err)
+			continue
+		}
+		if b != nil {
+			break
+		}
+	}
+	if b != nil {
+		return b, nil
+	}
+	if len(errs) > 0 {
+		err = errs[0]
+		for i := 1; i < len(errs); i++ {
+			err = fmt.Errorf("%v; %v", err, errs[i])
+		}
+		return nil, err
+	}
+	return nil, InvalidUpstreamErr
+}
+
 func (outline Outline) getConfigFromLink() ([]byte, error) {
+	if outline.Link == "" {
+		return nil, nil
+	}
 	client := http.Client{
 		Timeout: 10 * time.Second,
 	}
@@ -36,6 +74,9 @@ func (outline Outline) getConfigFromLink() ([]byte, error) {
 }
 
 func (outline Outline) getConfigFromSSH() ([]byte, error) {
+	if outline.SSHUsername == "" || (outline.SSHPrivateKey == "" && outline.SSHPassword == "") {
+		return nil, nil
+	}
 	var (
 		conf        *ssh.ClientConfig
 		authMethods []ssh.AuthMethod
@@ -86,14 +127,7 @@ func (outline Outline) GetServers() (servers []Server, err error) {
 			err = fmt.Errorf("outline.GetGroups: %v", err)
 		}
 	}()
-	var b []byte
-	if outline.Link != "" {
-		b, err = outline.getConfigFromLink()
-	}
-	if err != nil {
-		log.Printf("[warning] %v\n", err)
-		b, err = outline.getConfigFromSSH()
-	}
+	b, err := outline.getConfig()
 	if err != nil {
 		return
 	}
diff --git a/config/upstream.go b/config/upstream.go
index 70658be..2915e7b 100644
--- a/config/upstream.go
+++ b/config/upstream.go
@@ -9,6 +9,8 @@ type Upstream interface {
 	GetServers() (servers []Server, err error)
 }
 
+var InvalidUpstreamErr = fmt.Errorf("invalid upstream")
+
 func Map2upstream(m map[string]string, upstream interface{}) error {
 	v := reflect.ValueOf(upstream)
 	if !v.IsValid() {