modal.html.erb

<div class="header">
  <div class="header-img" style="background-image: url('/assets/inside.jpg')">
    <button data-toggle="modal" data-target=".photos-modal" class="view-photos">View Photos</button>
  </div>
  <div class="modal fade photos-modal" tabindex="-1" role="dialog" data-focus="true" aria-labelledby="myLargeModalLabel" aria-hidden="true">
    <div class="modal-dialog modal-lg modal-dialog-centered" role="document">
      <div class="modal-content">
        <div class="modal-header">
          <h5 class="modal-title"><%= @rental.title %></h5>
          <button type="button" class="close" data-dismiss="modal" aria-label="Close">
            <span aria-hidden="true">&times;</span>
          </button>
        </div>
        <div class="modal-body">
          <div id="modal-carousel" class="carousel slide" data-ride="carousel">
            <div class="carousel-inner">
              <% @rental.photos.each_with_index do |photo, index| %>
                <div class="<%= index == 0 ? 'carousel-item active' : 'carousel-item' %>">
                  <%= image_tag photo.url %>
                </div>
              <% end %>
            </div>
            <a class="carousel-control-prev" href="#modal-carousel" role="button" data-slide="prev">
              <span class="carousel-control-prev-icon" aria-hidden="true"></span>
              <span class="sr-only">Previous</span>
            </a>
            <a class="carousel-control-next" href="#modal-carousel" role="button" data-slide="next">
              <span class="carousel-control-next-icon" aria-hidden="true"></span>
              <span class="sr-only">Next</span>
            </a>
          </div>
        </div>
      </div>
    </div>
  </div>
</div>