When using cloud-init, a widely used tool for early initialization of cloud instances, the first line of a user-data script must indicate the type of content. For YAML configuration, the correct first line is #cloud-config.
* #cloud-config: This line tells cloud-init that the following content is YAML formatted and should be processed as a cloud-config file.
The other options are incorrect:
* A. cloud-config: Incorrect syntax.
* B. --- cloud-config: Incorrect syntax.
* C. #!/usr/bin/cloud-init: This is not the correct first line for a YAML configuration file.
* D. [cloud-config]: Incorrect syntax.
References:
* Cloud-Init Documentation - Examples