How to make Bootstrap 4 cards the same height in card-columns?

Question

You can either put the classes on the "row" or the "column"? Won't be visible on the cards (border) if you use it on the row. https://getbootstrap.com/docs/4.6/utilities/flex/#align-items

<div class="container">
    <div class="row">
        <div class="col-lg-4 d-flex align-items-stretch">
        <!--CARD HERE-->
        </div>
    </div>
</div>

UPDATE BS5 FULL HTML EXAMPLE

https://codepen.io/Kerrys7777/pen/QWgwEeG

I'm using Bootstrap 4 (Beta 2). Meanwhile the situations seems to have changed. I had the same problem and found an easy solution. This is my code:

<div class="container-fluid content-row">
    <div class="row">
        <div class="col-sm-12 col-lg-6">
            <div class="card h-100">
                … content card …
            </div>
        </div>
        … all the other cards … 
    </div>
</div>

With "col-sm-12 col-lg-6" I've made the cards responsive. With "card h-100" I've set all cards to the height of their parent column. On my system this works, but I'm not a pro. So, hopefully I helped someone.

Bootstrap 4 has all you need : USE THE .d-flex and .flex-fill class. Don't use the card-decks as they are not responsive. I used col-sm, you can use the .col class you want, or use col-lg-x the x means number of width column e.g 4 or 3 for best view if the post have many then 3 or 4 per column

Try to reduce the browser window to XS to see it in action :

<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" />

<link href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,500,500i,700,700i" rel="stylesheet">
<div class="container">
  <div class="row my-4">
    <div class="col">
      <div class="jumbotron">
        <h1>Bootstrap 4 Cards all same height demo</h1>
        <p class="lead">by djibe.</p>
        <span class="text-muted">(thx to BS4)</span>
        <p>Dependencies : standard BS4</p>
        <p>
          Enjoy the magic of flexboxes and leave the useless card-decks.
        </p>
        <div class="container-fluid">
          <div class="row">
            <div class="col-sm d-flex">
              <div class="card card-body flex-fill">
                A small card content.
              </div>
            </div>
            <div class="col-sm d-flex">
              <div class="card card-body flex-fill">
                "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor
                in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
              </div>
            </div>
            <div class="col-sm d-flex">
              <div class="card card-body flex-fill">
                Another small card content.
              </div>
            </div>
          </div>
        </div>
      </div>
    </div>
  </div>

You can apply the class h-100, which stands for height 100%.

UPDATE: In Bootstrap 4, flexbox is now default, and each card-deck row will contain 3 cards. The cards will fill to full height.

http://codeply.com/go/x91w5Cl6ip

The Bootstrap 4 alpha card-columns uses CSS3 columns which don't really support equal heights (except column-fill which is only suppored in Firefox).

If you instead enable Bootstrap 4 flexbox mode, you could instead use the card-deck and a little CSS to equalize the height and wrap every 3 columns.

@media (min-width:34em) {
    .card-deck > .card
    {
        width: 29%;
        flex-wrap: wrap;
        flex: initial; 
    }
}

http://codeply.com/go/YFFFWHVoRB

Related
Bootstrap 4 Cards of same height in columns

Here is how I did it:

CSS:

.my-flex-card > div > div.card {
    height: calc(100% - 15px);
    margin-bottom: 15px;
}

HTML:

<div class="row my-flex-card">
    <div class="col-lg-3 col-sm-6">
        <div class="card">
            <div class="card-block">
                aaaa
            </div>
        </div>
    </div>
    <div class="col-lg-3 col-sm-6">
        <div class="card">
            <div class="card-block">
                bbbb
            </div>
        </div>
    </div>
    <div class="col-lg-3 col-sm-6">
        <div class="card">
            <div class="card-block">
                cccc
            </div>
        </div>
    </div>
    <div class="col-lg-3 col-sm-6">
        <div class="card">
            <div class="card-block">
                dddd
            </div>
        </div>
    </div>
</div>