UPDATE: For Bootstrap 5
The class name is now "float-end" instead of "pull-right"
<div class="alert alert-info clearfix">
<a href="#" class="alert-link">
Summary:Its some description.......testtesttest
</a>
<button type="button" class="btn btn-primary btn-lg float-end">
Large button
</button>
</div>
For Bootstrap 4 and under
Just add a simple pull-right class to the button, and make sure the container div is clearfixed:
<div class="alert alert-info clearfix">
<a href="#" class="alert-link">
Summary:Its some description.......testtesttest
</a>
<button type="button" class="btn btn-primary btn-lg pull-right">
Large button
</button>
</div>