portainer/app/docker/components/dashboard-cluster-agent-info/dashboardClusterAgentInfo.html

<rd-widget>
  <rd-widget-header icon="fa-tachometer-alt" title-text="Cluster information"></rd-widget-header>
  <rd-widget-body classes="no-padding">
    <table class="table">
      <tbody>
        <tr>
          <td>Nodes in the cluster</td>
          <td>{{ $ctrl.agentCount }}</td>
        </tr>
        <tr>
          <td colspan="2">
            <div class="btn-group" role="group" aria-label="...">
              <a ui-sref="docker.swarm.visualizer"><i class="fa fa-object-group space-right" aria-hidden="true"></i>Go to cluster visualizer</a>
            </div>
          </td>
        </tr>
      </tbody>
    </table>
  </rd-widget-body>
</rd-widget>