AWS S3 Access Denied Only Sometimes

Question

I have been trying for days to get upload file from the aws-sdk for javascript to an s3 bucket. I have added the correct CORS policy and for testing purposes the bucket has public permissions. File upload only works 50% of the time though.

I am trying to upload 3-4 files in immediate succession from my website but I am getting access denied after the 2nd one. For some reason the first 2 upload successfully but the 3rd onwards fail. I have no idea if i have uncovered a glitch or if there is something I have done wrong.

My CORs policy is. I have also tried

`<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
    <AllowedOrigin>http://*</AllowedOrigin>
    <AllowedOrigin>https://*</AllowedOrigin>
    <AllowedMethod>PUT</AllowedMethod>
    <AllowedMethod>POST</AllowedMethod>
    <AllowedMethod>GET</AllowedMethod>
    <AllowedMethod>DELETE</AllowedMethod>
    <MaxAgeSeconds>3000</MaxAgeSeconds>
    <ExposeHeader>ETag</ExposeHeader>
    <AllowedHeader>*</AllowedHeader>
</CORSRule>
</CORSConfiguration>` 

I have also tried:

<AllowedOrigin>*</AllowedOrigin>

To no success.

To upload files I use temporary credentials from the aws-cognito sdk for js. The code I use to upload files is as follows:

function uploadFile(fileData,callback){
var file = fileData[4];
var key = "";
for(i=0; i<3; i++){
var temp = Math.ceil(Math.random()*1000000000000)
key=key+temp;
}

AWS.config.sessionToken= mySessionToken;
AWS.config.accessKeyId= myAccessKey;
AWS.config.secretAccessKey= mySecretKey;
AWS.config.region= myRegion;
var bucket = new AWS.S3({params: {Bucket: myBucketName}});
var params = {Key: key, ContentType: file.type, Body: file, ACL:'bucket-owner-
full-control'};
bucket.upload(params, function (err, data) {
if (err) {

callback(false,err,fileData);

}
else{
callback(true,"",fileData);
}
});

}

If it matters the website I am uploading from is hosted on an ec2 instance.

I know there are alot of posts about how to get file uploads to work with S3 but I have never seen any where it only works a portion of the time. I assume the credentials I use and my CORS configuration is correct because otherwise the uploads would never work right?

Thanks in advance for the help!

Edit:

This error only occurs on the 3rd sequential upload and onwards. The first and second file I upload have no errors and are successful.

The error code I receive is as follows:

Put [S3Instance] 403 Forbidden

<Error>
<Code>
AccessDenied
</Code>
<Message>
Access Denied
</Message>
<RequestId>
RequestId
</RequestId>
<HostId>
HostId
</HostId>
</Error>

Answer 1

I had the same problem, I attached the two strategies: AWSLambdaExecute and AWSLambdaBasicExecutionRole to the IAM role associated with my lambda and that solved the problem.