_ec2_tag.html.erb

<tr>
  <td>
    <%= f.text_field(:name, ... %>
  </td>
  <td>
    <%= f.text_field(:value, ... %>
  </td>
  <td>
    <%= link_to_remove_fields(_('Remove'), f) if f.object.new_record? %>
  </td>
</tr>

form.html.erb

<div id="ec2_tags">
  <table>
    <!-- with cols name, value, action -->
    <% tags.each do |key, val| %>
      <%= f.fields_for :tags, OpenStruct.new(name: key, value: val) do |fields| %>
        <%= render "compute_resources/ec2_tag", :f => builder %>
      <% end %>
    <% end %>
    <%= link_to_add_fields('+ ' + _("Add tag"), f, :tags, "compute_resources/ec2_tag", { :target => '#ec2_tags' }) %>
  </table>
</div>