How to create a file without any content using CloudFormation Init? - amazon-web-services

Question

I want an empty file to be created by CloudFormation.
I tried providing an empty string in the 'content' field in my CloudFormation template yaml file.
Resources:
Instance:
Type: AWS::EC2::Instance
Metadata:
AWS::CloudFormation::Init:
config:
files:
/var/log/app.log:
content: ""
mode: '000646'
I get the following error: File specified without source or content
2023-01-10 14:32:55,132 [DEBUG] Writing content to /var/log/app.log
2023-01-10 14:32:55,132 [ERROR] Error encountered during build of config: File specified without source or content
Traceback (most recent call last):
File "/usr/lib/python3.7/site-packages/cfnbootstrap/construction.py", line 579, in run_config
CloudFormationCarpenter(config, self._auth_config, self.strict_mode).build(worklog)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/construction.py", line 267, in build
self._config.files, self._auth_config)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/file_tool.py", line 131, in apply
self._write_file(f, attribs, auth_config)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/file_tool.py", line 221, in _write_file
raise ToolError("File specified without source or content")
cfnbootstrap.construction_errors.ToolError: File specified without source or content
2023-01-10 14:32:55,137 [ERROR] -----------------------BUILD FAILED!------------------------
2023-01-10 14:32:55,137 [ERROR] Unhandled exception during build: File specified without source or content
Traceback (most recent call last):
File "/opt/aws/bin/cfn-init", line 181, in <module>
worklog.build(metadata, configSets, strict_mode)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/construction.py", line 137, in build
Contractor(metadata, strict_mode).build(configSets, self)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/construction.py", line 567, in build
self.run_config(config, worklog)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/construction.py", line 579, in run_config
CloudFormationCarpenter(config, self._auth_config, self.strict_mode).build(worklog)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/construction.py", line 267, in build
self._config.files, self._auth_config)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/file_tool.py", line 131, in apply
self._write_file(f, attribs, auth_config)
File "/usr/lib/python3.7/site-packages/cfnbootstrap/file_tool.py", line 221, in _write_file
raise ToolError("File specified without source or content")
cfnbootstrap.construction_errors.ToolError: File specified without source or content
I get the same error if I omit the 'content' field.
Can you tell me the proper way to instruct CloudFormation to create an empty file?

Answer 1

You need to specify a content. If you really want to create an empty file, then I suggest to use commands.

Answer 2

As brushtakopo pointed out, CloudFormation Init doesn't support creating empty files so the only option appears to be to use a command.
I just wanted to include the corresponding command since he didn't include it in his answer.
Resources:
Instance:
Type: AWS::EC2::Instance
Metadata:
AWS::CloudFormation::Init:
config:
commands:
a_createLogFile:
command: "touch /var/log/app.log"
test: "test ! -e /var/log/app.log"
b_chmodLogFile:
command: "chmod 646 /var/log/app.log"
test: "test -e /var/log/app.log"
Note: The command prefixed with a_ creates the file and the command prefixed with b_ changes its access permissions. The prefixes are to ensure the first command is executed before the second command since CloudFormation executes commands in alphabetical order.
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-init.html
The commands are processed in alphabetical order by name.