Abort request on missing Graylog server version

If we fail to read the server version from Graylog,
stop using a fallback to 4.0.0 and retry the request
instead.

In scenarios with multiple Graylog nodes behind a load balancer,
this can lead to the sidecar temporarly stopping all collectors.

Fixes #481

api/graylog.go

@@ -42,22 +42,20 @@ var (
 )
 
 func GetServerVersion(httpClient *http.Client, ctx *context.Ctx) (*GraylogVersion, error) {
-	// In case of an error just assume 4.0.0
-	fallbackVersion, _ := NewGraylogVersion("4.0.0")
-
 	c := rest.NewClient(httpClient, ctx)
 	c.BaseURL = ctx.ServerUrl
 	r, err := c.NewRequest("GET", "/", nil, nil)
 	if err != nil {
 		log.Errorf("Cannot retrieve server version %v", err)
-		return fallbackVersion, err
+		return nil, err
 	}
 	versionResponse := graylog.ServerVersionResponse{}
 	resp, err := c.Do(r, &versionResponse)
 	if err != nil || resp == nil {
 		log.Errorf("Error fetching server version %v", err)
-		return fallbackVersion, err
+		return nil, err
 	}
+	log.Debugf("Graylog server version %v", versionResponse.Version)
 	return NewGraylogVersion(versionResponse.Version)
 }
 

services/periodicals.go

@@ -49,7 +49,10 @@ func StartPeriodicals(context *context.Ctx) {
 			}
 			firstRun = false
 
-			serverVersion, _ := api.GetServerVersion(httpClient, context)
+			serverVersion, err := api.GetServerVersion(httpClient, context)
+			if err != nil {
+				continue
+			}
 
 			// registration regResponse contains configuration assignments
 			regResponse, err := updateCollectorRegistration(httpClient, lastRegResponse.Checksum, context, serverVersion)