How to set an button align-right with Bootstrap?

Try this:

<div class="row">
<div class="alert alert-info" style="min-height:100px;">
    <div class="col-xs-9">
        <a href="#" class="alert-link">Summary:Its some
           description.......testtesttest</a>  
    </div>
    <div class="col-xs-3">
        <button type="button" class="btn btn-primary btn-lg">Large      button</button>
    </div>
 </div>
</div>

Demo:

http://jsfiddle.net/Hx6Sx/1/

This worked for me:

<div class="text-right">
    <button type="button">Button 1</button>
    <button type="button">Button 2</button>
</div>

Bootstrap 5 implementation:

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>

---

Bootstrap 4 (and under) implementation:

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>