How uploading to S3 through PHP script on EC2 works?

Question

Please help me understand the process of uploading files to Amazon S3 server via PHP. I have a website on EC2, which will have PHP script for uploading file to S3 server from client's machine. What I need to understand, is whether the file will go directly to S3 from client's machine, or if it will first be uploaded onto EC2, and then to S3. If it's the second option, then how can I optimize the upload so that file goes directly to S3 from client's machine?

Answer 1

It is possible to upload a file to S3 using any of the scenarios you specified.

In the first scenario, the file gets uploaded to your PHP backend on EC2 and then you upload it from PHP to S3 via a PUT request. Basically, in this scenario, all uploads pass through your EC2 server.

The second option is to upload the file directly to S3 from the client's browser. This is done by using a POST request directly to S3 and a policy that you can generate using your PHP logic, and attach it to the POST request. This policy is basically a set of rules that allow S3 to accept the upload (without it anyone would be able to upload anything in your bucket).

In this second scenario, your PHP scripts on EC2 will only need to generate a valid policy for the upload, but the actual file that's being uploaded will go directly to S3 without passing trough your EC2 server.

You can get more info on the second scenario here:

http://aws.amazon.com/articles/1434

even if it's not PHP specific, it explains how to generate the policy and how to form the POST request.

You can also get more information by reading through the API docs for POST requests:

http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html

EDIT: The official AWS SDK for PHP contains a helper class for doing this: http://docs.aws.amazon.com/aws-sdk-php-2/latest/class-Aws.S3.Model.PostObject.html