- `provider` (required) - the name of the provider ("gce" in this case).
- `tag_value` (required) - the value of the tag to auto-join on.
- `project_name` (optional) - the name of the project to auto-join on. Discovered if not set.
- `zone_pattern` (optional) - the list of zones can be restricted through an RE2 compatible regular expression. If omitted, servers in all zones are returned.
- `credentials_file` (optional) - the credentials file for authentication. See below for more information.
#### Authentication & Precedence
- Use credentials from `credentials_file`, if provided.
- Use JSON file from `GOOGLE_APPLICATION_CREDENTIALS` environment variable.
- Use JSON file in a location known to the gcloud command-line tool.
- On Windows, this is `%APPDATA%/gcloud/application_default_credentials.json`.
- On other systems, `$HOME/.config/gcloud/application_default_credentials.json`.
- On Google Compute Engine, use credentials from the metadata
server. In this final case any provided scopes are ignored.