Otdfbt

I have the following Dockerrun.aws.json:

 "AWSEBDockerrunVersion": "1",
 "Authentication": 
 "Bucket": "bucket-of-another-aws-account",
 "Key": "docker/.dockercfg"
 ,
 "Image": 
 "Name": "docker-image"
 ,
 "Ports": [
 
 "ContainerPort": "8080"
 
 ]

The Elastic Beanstalk Environment with our Docker container is running in the customer's AWS account and the S3 bucket with the .dockercfg belongs to our AWS account.

For testing purposes I set the bucket policy principle to * so that anyone can download the .dockercfg file. Nevertheless Elastic Beanstalk is not able to download that file ("Failed to download authentication credentials docker/.dockercfg from bucket-of-another-aws-account").

The next test was to move the file to an S3 bucket within the customer's AWS account. That worked.

Question is: Is it possible to use a bucket of another account in the Dockerrun.aws.json? I could not find any hints in the documentation and I don't want to give the DockerHub API key to our customer.

We managed to overcome the "Failed to download authentication credentials" like this:

1) In account B (the one trying to access the remote bucket), look in the Elastic Beanstalk environments' settings for the instance role name it is using (configuration, instances (cog), Instance profile)

2) Still in account B, in the IAM manager, go to Roles and find the ec2 role from the previous step that EB is using for the instances, and attach an inline policy

 "Version": "2012-10-17",
 "Statement": [
 
 "Sid": "BucketAccess",
 "Effect": "Allow",
 "Action": [
 "s3:List*",
 "s3:GetBucketLocation"
 ],
 "Resource": [
 "arn:aws:s3:::bucket-of-another-aws-account"
 ]
 ,
 
 "Sid": "S3ObjectAccess",
 "Effect": "Allow",
 "Action": [
 "s3:GetObject*",
 "s3:List*"
 ],
 "Resource": [
 "arn:aws:s3:::bucket-of-another-aws-account/*"
 ]
 
 ]

3) on the target s3 bucket in Account A attach a policy (where 222222222222 is your account no of Account B)

 "Version": "2012-10-17",
 "Statement": 
 "Sid": "AccountBAccess1",
 "Effect": "Allow",
 "Principal": 
 "AWS": "222222222222"
 ,
 "Action": "s3:*",
 "Resource": [
 "arn:aws:s3:::bucket-of-another-aws-account",
 "arn:aws:s3:::bucket-of-another-aws-account/*"
 ]
 

I know its a late answer to the OP (made me think of https://xkcd.com/979/ ) but I also could not find any concise or definitive answer in the docs online, and with more people moving to AWS and Elastic Beanstalk I hope this can be of use to others!