File upload destination

I am a bit confused about how a File Upload works.

Assuming I have a simple HTML Form that upload a file to Web Server 2, so:

<form action="http://webserver2/index.php" method="post" enctype="multipart/form-data">
   Select image to upload:
   <input type="file" id="file">
   <input type="submit" value="Upload File" name="submit">
</form>

As you can see the form action points to "webserver2" so the file data will get received and read from Web Server 2, which will be able to save the file.

Question: Is the file upload directly to Web Server 2 or passing through Web Server 1 first?

My need is: uploading the file to Web Server 2 but retaining a copy on Web Server 1. Is this possible / already happening?

Thank you