AWS SDK to S3 works fine from my shared hosting but not from EC2

I have a working account on Amazon S3. I have used it together with my shared hosting and it has worked well. I have now setup an Amazon EC2 instance with Amazon Linux (a similar CentOS / Redhat Linux) and installed apache and php with

sudo yum install -y httpd24 php56

and added www group etc from this page. Everything else expect MySQL. http://ift.tt/1aE3oJu

Installed AWS SDK to EC2 from composer and it worked great.

I can run simple PHP scripts on EC2 without problems, e.g

<?php phpinfo(); ?>

But this example code is not working on my EC2.

require 'vendor/autoload.php';
use Aws\Common\Aws;
use Aws\S3\S3Client;

 $aws = S3Client::factory(array(
    'key' => 'CORRECT KEY, USING THE SAME ON MY SHARED HOSTING',
    'secret' => 'CORRECT SECRET, USING THE SAME ON MY SHARED HOSTING',
//  'region'  => 'us-east-1',
));

 $bucket = 'CORRECT BUCKET';

$objects = $aws->getIterator('ListObjects', array('Bucket' => $bucket));

echo "Keys retrieved!\n";
foreach ($objects as $object) {
    echo $object['Key'] . "\n";
}

This code works fine on my shared hosting but not on EC2. I have tested to list all buckets and other simple code that works fine on my shared hosting but not on EC2.

I can see that the SDK is included on my page on EC2 with this.

$included_files = get_included_files();

foreach ($included_files as $filename) {
    echo "$filename\n";
}

Have I missed something on EC2? Why is the same code working on my shared hosting but not on EC2 to the same Amazon S3 account/bucket. No error messages on the page or something else that indicates that something is wrong.