code: func (evc ExternalEtcdVersionCheck) configRootCAs(config *tls.Config) (*tls.Config, error) {
  	var CACertPool *x509.CertPool
  	if evc.Etcd.External.CAFile != "" {
  		CACert, err := ioutil.ReadFile(evc.Etcd.External.CAFile)
  		if err != nil {
  			return nil, errors.Wrapf(err, "couldn't load external etcd's server certificate %s", evc.Etcd.External.CAFile)
  		}
  		CACertPool = x509.NewCertPool()
  		CACertPool.AppendCertsFromPEM(CACert)
  	}
  	if CACertPool != nil {
  		if config == nil {
  			config = &tls.Config{}
  		}
  		config.RootCAs = CACertPool
  	}
  	return config, nil
  }
docs: // configRootCAs configures and returns a reference to tls.Config instance if CAFile is provided