add workflow for docker

[sed-i]

This PR introduces a new workflow:

• docker-playground, which is useful for uploading image resources to charmcraft and basically anything related to oci images. Since docker iptables rules conflict with juju/lxd/multipass, it is convenient to have a separate instance for docker.

[valentincanonical]

Hey there! Dropping a few ideas here, from the demo I saw today:

• integrate with an open source UI for OCI runtimes, like Portainer (IMO, K8s options should be left to other projects such as microk8s.io)
• once multipass launch is complete, provide a few getting started commands such as enabling the UI, launching a container (happy for you to use https://hub.docker.com/u/ubuntu or https://hub.docker.com/_/ubuntu as examples) or listing the running containers

a few threads to explore,

• how are upgrades handled?
• docker-compose integration
• out of disk space issues when the VM starts to fill with images (help message on how to resize? and/or how to clear some space?)
• pausing/resuming the VM when it is not being used (and, how will I be warned if I try to run a command while the VM is stopped?)

[Saviq]

• integrate with an open source UI for OCI runtimes, like Portainer

Should be doable, yeah.

(IMO, K8s options should be left to other projects such as microk8s.io)

Any other opinions on this?

• once multipass launch is complete, provide a few getting started commands such as enabling the UI, launching a container (happy for you to use https://hub.docker.com/u/ubuntu or https://hub.docker.com/_/ubuntu as examples) or listing the running containers

Totally, we want to have a "first run" experience where a message is printed after multipass launch docker for the first time.

• how are upgrades handled?

Snaps get auto updated, unattended-upgrades is configured with defaults, we could maybe tweak those. Anything else in your mind?

• docker-compose integration

👍

• out of disk space issues when the VM starts to fill with images (help message on how to resize? and/or how to clear some space?)

That sounds like a generic thing, we could warn about low disk on multipass shell and/or multipass exec (and by extension, on alias execution).

• pausing/resuming the VM when it is not being used (and, how will I be warned if I try to run a command while the VM is stopped?)

Executing the alias would kick the machine to life. Pausing is problematic as how do we know it's not being used?

[valentincanonical]

Snaps get auto updated, unattended-upgrades is configured with defaults, we could maybe tweak those. Anything else in your mind?

Sounds right for patches/security updates. Upgrading (esp. major) versions may be trickier. Only something to keep in mind I guess. Not sure I have an answer!

• out of disk space issues when the VM starts to fill with images (help message on how to resize? and/or how to clear some space?) That sounds like a generic thing, we could warn about low disk on multipass shell and/or multipass exec (and by extension, on alias execution).

👍

• pausing/resuming the VM when it is not being used (and, how will I be warned if I try to run a command while the VM is stopped?) Executing the alias would kick the machine to life. Pausing is problematic as how do we know it's not being used?

Right, pausing needs to be opt-in. Might be something to document in the post-launch message.