title: aws s3 sync not working as expected
body: <p>I'm trying to set up a one-way directory sync process from one local PC to an AWS EC2 instance via S3.</p>
  
  <p>Both machines are Windows.</p>
  
  <p>I tried using the command line interface.</p>
  
  <p>On the local machine:</p>
  
  <pre><code>aws s3 sync source_dir s3://bucket --region eu-central-1
  </code></pre>
  
  <p>This command seems to to work well. If there is nothing new, nothing is sync'ed. So far so good.</p>
  
  <p>On the AWS instance:</p>
  
  <pre><code>aws s3 sync s3://bucket target_dir --region eu-central-1
  </code></pre>
  
  <p>With this command, I have a an issue.  Whenever I run it, there is always something to download (it seems to be always the same set of files, perhaps they are all of them, but it seems a subset of them).  My expectation was that once in sync, running the command again produced no downloads.</p>
  
  <p>I granted these permissions in the policy:      </p>
  
  <pre><code>"Action": [
       "s3:GetObject",
       "s3:GetObjectAcl",
       "s3:ListBucket",
       "s3:PutObject",
       "s3:PutObjectAcl" 
  ],
  "Resource": [
       "arn:aws:s3:::bucket_name",
       "arn:aws:s3:::bucket_name/*" 
  ]
  </code></pre>
  
  <p>Am I missing anything in this setup so that I do not get files downloaded if there is nothing to download when I run the second sync?</p>