code: func HTTPGetCheck(url string, timeout time.Duration) Check {
  	client := http.Client{
  		Timeout: timeout,
  		// never follow redirects
  		CheckRedirect: func(*http.Request, []*http.Request) error {
  			return http.ErrUseLastResponse
  		},
  	}
  	return func() error {
  		resp, err := client.Get(url)
  		if err != nil {
  			return err
  		}
  		resp.Body.Close()
  		if resp.StatusCode != 200 {
  			return fmt.Errorf("returned status %d", resp.StatusCode)
  		}
  		return nil
  	}
  }
docs: // HTTPGetCheck returns a Check that performs an HTTP GET request against the
  // specified URL. The check fails if the response times out or returns a non-200
  // status code.