When using awscli to create CloudFormation stacks, there’s a pre-create step of template validation that checks for template syntax issues:

aws cloudformation validate-template --template-body file:///path/to/template.json

The URI prefix file:// indicates that we are using local templates while templates at web-accessible locations like your S3 bucket are accessed using the –template-url option. For more information see the awscli docs or CLI help:

aws cloudformation validate-template help

For local templates, make sure you don’t forget the file:// URI and try to refer to the template via normal filesystem paths, otherwise you’ll get a confusing syntax error.

Without file:// URI:

aws cloudformation validate-template --template-body /Users/foo/git-repos/aws-mojo/cloudformation/aws-deploy-codecommit-repo.yml

An error occurred (ValidationError) when calling the ValidateTemplate operation: Template format error: unsupported structure.

That’s a rather unhelpful error message that makes me think I’ve got some sort of template content error.

When we run the same command with file:// URI, we get the expected output:

aws cloudformation validate-template --template-body file:///Users/foo/git-repos/aws-mojo/cloudformation/aws-deploy-codecommit-repo.yml
{
   "Description": "CloudFormation template for creating a CodeCommit repository along with a SNS topic for repo activity trigger notifications",
   "Parameters": [
 {
   "NoEcho": false,
   "Description": "Email address for SNS notifications on repo events",
   "ParameterKey": "Email"
 },
 {
   "NoEcho": false,
   "Description": "A unique name for the CodeCommit repository",
   "ParameterKey": "RepoName"
 },
 {
   "DefaultValue": "Dev",
   "NoEcho": false,
   "Description": "Environment type (can be used for tagging)",
   "ParameterKey": "Environment"
 },
 {
   "NoEcho": false,
   "Description": "A description of the CodeCommit repository",
   "ParameterKey": "RepoDescription"
 }
 ]
}