Adding dry-run mode.

[jsargiot]

This mode allows to process template resources and run check_cmd on the result without updating target files nor running reload_cmd. This mode is useful to run monitoring checks where it's nice to be able to detect problems with the templates at rendering and application level.

Example usage:

Confd is configured to update nginx.conf file and you need a way to detect problems with template. Right now -noop is ok to test template rendering but it won't catch problems in the nginx configuration (like duplicated upstreams), so this new command allows to render the template and run nginx template check.

[bacongobbler]

Hey @jsargiot! So essentially this is just a dry run? Perhaps --dry-run would be a better name to call this flag to follow the convention of other projects. This sounds like a handy feature to support.

[jsargiot]

Perhaps --dry-run would be a better name to call this flag to follow the convention of other projects.

To me --dry-run means "pretend you are doing things" in this case the template is being rendered and check_cmd is actually executed... so it would feel a bit akward to me but I don't really have a strong opposition to it.