Support for generic artifact download

[pickgr]

To date, we have primarily utilized the Atlas artifact registry for pointers to other resources (for example, AMI IDs). There is a growing use case for artifacts with archives attached. The driver for opening this ticket is the versioning of application archives for AWS Lambda.

While upload and indexing in Atlas is fairly straight forward, the Terraform language is lacking either a form of URL interpolation for remote file download or the ability for the Lambda function resource to leverage the Atlas artifact registry. There is support for a versioned S3 bucket, which is a little surprising, as HashiCorp typically positions their solution ahead of alternatives in the beginning. I suspect this feature will be added at some point soon.

To continue down the path of remaining agnostic to our artifact provider and thus keeping our Terraform code generic, the proposed solution for these limitations at this time would be to extend the build framework to support Atlas artifacts that have binaries associated with them. This would function similar to the existing logic for querying and retrieving key values, but would include an additional flag for artifact download and specification of download path.

• Extend build framework Atlas plug-in to support artifact download
• Verify with Lambda use case by modeling demonstrating that the artifact could be resolved during a Terraform execution without any race conditions