title: ClientError: An error occurred (403) when calling the HeadObject operation: Forbidden
body: <p>I'm creating an AWS Lambda Function that tries to download a file (s3.download_file) to a temp dir that I create using the <em>tempfile</em> library from Python (3.6). Then, I make some transformations to the file and I need to upload it (s3.upload_file) again. I'm confident about the life cycle from my temp dir, when the Lambda finish its job, the temp dir is going to destroy itself. The Lambda returns an error related to forbidden HeadObject operation. The exact error is:</p>
  
  <p>"An error occurred (403) when calling the HeadObject operation: Forbidden"</p>
  
  <p>How can I debug this error? I already checked several sources, some of them talk about adjusting policies, check permissions, but my question is, there is some step by step (that AWS in its documentation doesn't have), that allows me to survive to this problem?</p>