Return a clear error when bind-mounting relative path

[psviderski]

When attempting to deploy the following compose.yaml:

services:
  atomdns:
    #    image: registry.science.ru.nl/cncz/sys/image/atomdns:latest
    image: debian:bookworm-slim
    entrypoint:
      - /bin/sh
      - "-c"
      - "ls -l /conf/Conffile"
    x-ports:
      - ctrl.uncld.science.ru.nl:443/https

    deploy:
      replicas: 1

    volumes:
      - ./atomdns:/conf:ro
      - atomdns_data:/var/lib/atomdns

volumes:
  atomdns_data:

it will attempt to mount /Users/richard/projects/uc/atom/atomdns on the remote machine but this is the path resolved from ./atomdns on the local machine.

$ docker container inspect d32e134ec731
...
 "Mounts": [
            {
                "Type": "bind",
                "Source": "/Users/richard/projects/uc/atom/atomdns",
                "Destination": "/conf",
                "Mode": "",
                "RW": false,
                "Propagation": "rprivate"
            },
            {
                "Type": "volume",
                "Name": "atomdns_data",
                "Source": "/var/lib/docker/volumes/atomdns_data/_data",
                "Destination": "/var/lib/atomdns",
                "Driver": "local",
                "Mode": "z",
                "RW": true,
                "Propagation": ""
            }
        ],
...

We should fail with a clear error message that mounting a relative path won't work as a user might expect. And we can hint that using configs is likely what the user needs.

See original issue: #330

[miekg]

once you've parsed a spec all paths are absolute, so this needs to be done very early, or even before loading a spec brrr (on the cmdline uc run is slightly easier)

[psviderski]

Yeah, that's true. I think we should be able to use the mechanism for registering custom transformers to hook into the load process and check the values in the original config without modifying anything:

uncloud/pkg/client/compose/project.go

Lines 23 to 25 in 0e820f9

	registerComposeOverrides.Do(func() {
	transform.RegisterDefaultValue("services.*.deploy.update_config", setUpdateConfigDefaults)
	})