Better error message on startup healthcheck

client.go

@@ -1086,6 +1086,7 @@ func (c *Client) startupHealthcheck(timeout time.Duration) error {
 	c.mu.Unlock()
 
 	// If we don't get a connection after "timeout", we bail.
+	var lastErr error
 	start := time.Now()
 	for {
 		// Make a copy of the HTTP client provided via options to respect
@@ -1104,13 +1105,18 @@ func (c *Client) startupHealthcheck(timeout time.Duration) error {
 			res, err := cl.Do(req)
 			if err == nil && res != nil && res.StatusCode >= 200 && res.StatusCode < 300 {
 				return nil
+			} else if err != nil {
+				lastErr = err
 			}
 		}
 		time.Sleep(1 * time.Second)
 		if time.Now().Sub(start) > timeout {
 			break
 		}
 	}
+	if lastErr != nil {
+		return errors.Wrapf(ErrNoClient, "health check timeout: %v", lastErr)
+	}
 	return errors.Wrap(ErrNoClient, "health check timeout")
 }
 

client_test.go

@@ -279,6 +279,9 @@ func TestClientHealthcheckStartupTimeout(t *testing.T) {
 	if !IsConnErr(err) {
 		t.Fatal(err)
 	}
+	if !strings.Contains(err.Error(), "connection refused") {
+		t.Fatalf("expected error to contain %q, have %q", "connection refused", err.Error())
+	}
 	if duration < 5*time.Second {
 		t.Fatalf("expected a timeout in more than 5 seconds; got: %v", duration)
 	}