I had this after reading #12537 and #9047. Currently `DockerOperator`’s `volumes` argument is passed directly to docker-py’s `bind` (aka `docker -v`). But `-v`’s behaviour has long been problematic, and [Docker has been pushing users to the new `--mount` syntax instead](https://docs.docker.com/storage/bind-mounts/#choose-the--v-or---mount-flag). With #12537, it seems like `-v`’s behaviour is also confusing to some Airflow users, so I want to migrate Airflow’s internals to `--mount`.

However, `--mount` has a different syntax to `-v`, and the behaviour is also slightly different, so for compatibility reasons we can’t just do it under the hood. I can think of two possible solutions to this:

A. Deprecate `volumes` altogether and introduce `DockerOperator(mounts=...)`

This will emit a deprecation warning when the user passes `DockerOperator(volumes=...)` to tell them to convert to `DockerOperator(mounts=...)` instead. `volumes` will stay unchanged otherwise, and continue to be passed to bind mounts.

`mounts` will take a list of [`docker.types.Mount`](https://docker-py.readthedocs.io/en/stable/api.html#docker.types.Mount) to describe the mounts. They will be passed directly to the mounts API. Some shorthands could be useful as well, for example:

```python
DockerOperator(
    ...
    mounts=[
        ('/root/data1', './data1'),  # Source and target, default to volume mount.
        ('/root/data2', './data2', 'bind'),  # Bind mount.
    ],
)
```

B. Reuse `volumes` and do introspection to choose between binds and mounts

The `volumes` argument can be augmented to also accept `docker.types.Mount` instances, and internally we’ll do something like

```python
binds = []
mounts = []
for vol in volumes:
    if isinstance(vol, str):
        binds.append(vol)
    elif isintance(vol, docker.types.Mount):
        mounts.append(vol)
    else:
        raise ValueError('...')
if binds:
    warnings.warn('...', DeprecationWarning)
```

and pass the collected lists to binds and mounts respectively.

I’m very interested in hearing thoughts on this.


**Are you willing to submit a PR?**
Yes

**Related Issues**

* #12537: Confusing on the bind syntax.
* #9047: Implement mounting in `DockerSwarmOperator` (it’s a subclass of `DockerOperator`, but the `volumes` option is currently unused).

airflow/providers/docker/operators/docker.py
"""Run a Docker container with the provided image"""
        self.log.info('Starting docker container from image %s', self.image)
        with TemporaryDirectory(prefix='airflowtmp', dir=self.host_tmp_dir) as host_tmp_dir:
            self.volumes.append(f'{host_tmp_dir}:{self.tmp_dir}')
            if not self.cli:
                raise Exception("The 'cli' should be initialized before!")
            self.container = self.cli.create_container(
                command=self.format_command(self.command),
                name=self.container_name,
                environment={**self.environment, **self._private_environment},
                host_config=self.cli.create_host_config(
                    auto_remove=False,
                    binds=self.volumes,
                    network_mode=self.network_mode,
                    shm_size=self.shm_size,
                    dns=self.dns,
                    dns_search=self.dns_search,
                    cpu_shares=int(round(self.cpus * 1024)),
                    mem_limit=self.mem_limit,
                    cap_add=self.cap_add,
                    extra_hosts=self.extra_hosts,
                    privileged=self.privileged,
                ),
                image=self.image,
                user=self.user,
                entrypoint=self.format_command(self.entrypoint),
                working_dir=self.working_dir,