Is there an option to use `--config` and Go templates for containers?

[TheRealBecks]

In containers/podlet#206 we got an feature request to support compose configs, but I can't see such an option in Podman? Especially configs with (Golang or other) templates would be a great feature as it's already in use by Docker and docker-compose.

Docker has a config feature that can be used to create configs for services. Furthermore there's a --template-driver option that can be used to specify a template engine like --template-driver golang. This feature is useful when dynamic configs (or files) shell be linked into a container, e.g. a templated nginx.conf.

Therefore docker-compose also supports configs as can be seen here. But there's no support for the template_driver as of now, but Docker defaults to golang as far as I can tell. compose-spec also has no template_driver, yet, but I can create an issue over there if needed.

The questions here are:

• Does Podman has an equivalent feature?
• Is there a Quadlet option to be used with?
• Has this config feature already been discussed? I wasn't able to find a related issue

[Luap99]

The docker docs make it clear this only work with docker swarm which we never supported and have no plans to support, for multi node use cases we recommend kubernetes.

And on a signle node it is not clear to me what this is adding over the regular volumes/bind mounts? Personally I would be against adding yet another option to mount content into a container. This can trivially be done by just writing to a tmp file on the host and bind mounting that one.

[TheRealBecks]

@Luap99 Yes, you are right, that Docker config feature is Docker Swarm related, haven't seen that it's Swarm related!

That being said: Theres still a configsoption in the YAML notation ofcompose-spec. If there's not a docker command that can be used to render and mount the config files, how do they do it? Is the render feature "compose" (docker-compose, podman-compose` (<- not yet implemented) ) specific and a temporary file is being mounted into the container? Creating config files out of templates and mounting them into the container makes the admin live way easier 😀 Is Podman (with Quadlets) able to use a template engine?

[Luap99]

code suggest this is handled on the compose (client) site https://github.com/docker/compose/blob/ae92bef4e1d02bfb75afeafc0ce9334a133f952f/pkg/compose/secrets.go#L42-L69

Is Podman (with Quadlets) able to use a template engine?

just shell out to your engine of choice before calling podman. Other than that quadlet/systemd can use template untis and systemd specifiers.

Besides the compose code shows no signs of supporting templates there

[decentral1se]

Yes, the compose folx will not support template_driver: docker/compose#13598.

The reality is that a lot of compose configs are using configs/template_driver out in the wild and even for single-node docker swarm deployments (because it handles automagically zero-downtime deploys pretty OK).

There might not be much of a technical consistency to implement this but maybe we can figure out a way to translate these docker swarm practices into something podlet can consume and translate.

Work-arounds are fine as long as they are work-arounds which everyone can do. Happy to think along from the podlet side of things.