Transients

index.php

<?php

function get_my_expensive_data() {
    $cache_key = 'my-cache-key';
    $transient = get_transient( $cache_key );
    
    if ( $transient ) {
        return $transient;
    } else {
       $data = wp_remote_get( 'http://your-service.com' );
       set_transient( $cacke_key, $data, DAY_IN_SECONDS );
       
       return $data;
    }
}