Codebuild with SAM CLI Cross Account S3 issue - amazon-web-services

Question

I have a multi-account setup at my current company. I am using CodeBuild in Account B, I am running a buildspec that uploads a transformed sam template to an s3 bucket in Account A. So the Cloudformation package uploads the sam build of the code to the "account-a-bucket". The job successfully uploads the transformed template as defined in the artifacts section, to a bucket in Account B. The problem comes when trying to deploy the template in account C. Because codebuild creates the lambda code artifact in the build step and writes the object to the bucket outside of the account. When you go look at the actual lambda artifact depositied in the bucket, so s3:://account-a-bucket/e309uofijokasjdfokajsllsk , you will see in the object permission that it does not belong to any account. Therefore no one can access it. How do I make codebuild create the object in the other account bucket, so it is owned by an account?
To note as well, I already configured the Bucket Policy to grant access to account-a-bucket to all accounts in my organization, additionally the canonical ids of the accounts for permissions. So I know for a fact is the lambda artifact is created with no canonical account owner, however the artifact that is uploaded (in the artifact section of buildspec) is created under the account canonical id.
I know you can use, if for example I was uploading in the build phase using an
aws s3api copy-object --bucket destination_awsexammplebucket --key source_awsexamplebucket/myobject --acl bucket-owner-full-control
I could use --acl bucket-owner-full-control, but that is not a supported flag with aws cloudformation package.
env:
variables:
RELEASE_NUMBER: ""
MINOR_NUMBER: "value"
phases:
install:
runtime-versions:
docker: 18
build:
commands:
- echo Building Release Version $RELEASE_NUMBER
- pip install --user aws-sam-cli
- USER_BASE_PATH=$(python -m site --user-base)
- export PATH=$PATH:$USER_BASE_PATH/bin
- sam build -t template.yaml
- aws cloudformation package --template-file template.yaml --s3-bucket account-a-bucket --output-template-file TransformedTemplate.yaml
artifacts:
files:
- TransformedTemplate.yaml
discard-paths: yes

Answer 1

The 'aws cloudformation package' command does not have an "--acl" option which is the cause of the issue you are facing. This is an open issue [1] but one that has not got any traction.
For now, I am thinking you can parse out the S3 object key from 'TransformedTemplate.yaml', and then run the following command in your buildspec to put an ACL on the S3 object:
$ aws s3api put-object-acl --bucket account-a-bucket --key keyname --acl bucket-owner-full-control
For parsing a json file, 'jq' is probably the best utility. Since you are using Yaml, yq [2] seems to be an option though I have never tested it myself.
Ref:
[1] https://github.com/aws/aws-cli/issues/2681
[2] https://yq.readthedocs.io/en/latest/