googleapi：错误503：后端错误，golang中的backenderror

I'm trying to upload a file to Google Cloud Storage, i received notice error :

[ERROR] [ERROR] googleapi: Error 503: Backend Error, backendError

[ERROR] dial tcp 108.177.97.109:587: connectex: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.

intermittently I'm getting this exception from Google

In my source, at function:

func getGsUtil() (*st.Util, error) {
    c := GetMainConfig()
    return gcp.NewGSUtil(&gcp.GCPConfig{
        PrivateKeyPem: c.GCP.PrivateKeyPem,
        Email:         c.GCP.Email,
        ProjectID:     c.GCP.ProjectID,
    })
}

AND

func NewGSUtil(cfg *GCPConfig) (*st.Util, error) {
    pKeyFilePath := cfg.PrivateKeyPem
    if !ext.FileExists(pKeyFilePath) && !filepath.IsAbs(pKeyFilePath) {
        pKeyFilePath = filepath.Join(filepath.Dir(os.Args[0]), pKeyFilePath)
    }
    pemKeyBytes, err := ioutil.ReadFile(pKeyFilePath)

    if err != nil {
        return nil, err
    }
    conf := &jwt.Config{
        Email:      cfg.Email,
        PrivateKey: pemKeyBytes,
        Scopes: []string{
            storage.CloudPlatformScope,
            storage.DevstorageReadWriteScope,
        },
        TokenURL: google.JWTTokenURL,
    }

    // Initiate an http.Client
    client := conf.Client(context.Background())
    storageService, err := storage.New(client)

    if err != nil {
        return nil, err
    }

    // Verify service by get buckets list
    _, err = storageService.Buckets.List(cfg.ProjectID).Do()
    if err != nil {
        return nil, err
    }

    mSTUtil := &st.Util{
        Service:   storageService,
        ProjectId: cfg.ProjectID,
    }

    return mSTUtil, nil
}

after I call this handle the error is returned, i don't know if the error is due to the SMTP mail server or googleapi's service, the error error googleapi is returned first.

I tried searching for this error on google, is it an error connecting to the google service?

I don't know the error how will this be solved.