When using bootstrap 4 or 5, flexbox could be used to achieve desired effect:
<body class="d-flex flex-column min-vh-100">
<header>HEADER</header>
<content>CONTENT</content>
<footer class="mt-auto"></footer>
</body>
Please check the examples: Bootstrap 4 Bootstrap 5
In bootstrap 3 and without use of bootstrap. The simplest and cross browser solution for this problem is to set a minimal height for body object. And then set absolute position for the footer with bottom: 0 rule.
body {
min-height: 100vh;
position: relative;
margin: 0;
padding-bottom: 100px; //height of the footer
box-sizing: border-box;
}
footer {
position: absolute;
bottom: 0;
height: 100px;
}
Please check this example:
Bootstrap 3