docker-compose container name use dash (-) instead of underscore (_)

This naming convention difference appears to be a difference between Docker Compose versions v1 (Python) and v2 (Go). The latest docker/compose repo that is packaged with Docker Desktop is the golang version in the docker/compose v2 branch. Looking at the source code here in this branch:

// Separator is used for naming components
var Separator = "-"

The python branch source code is using the _ naming convention for components, here for example:

    def rename_to_tmp_name(self):
        """Rename the container to a hopefully unique temporary container name
        by prepending the short id.
        """
        if not self.name.startswith(self.short_id):
            self.client.rename(
                self.id, '{}_{}'.format(self.short_id, self.name)
            )

As to solving this, you may want to uninstall the compose included with Docker Desktop and revert to a 1.28.x version. The compose readme says you can use pip install docker-compose to install. The compose docs have a section about upgrading this and commands to migrate to v2: https://docs.docker.com/compose/install/#upgrading but your question suggests you want to stay with the _ v1 naming convention.

As mentioned in comments, the following options retain the compose compatibility:

1. use --compatibility flag with docker-compose commands
2. set COMPOSE_COMPATIBILITY=true environment variable

Other doc links:

• Backward compatibility is discussed here: https://github.com/docker/compose#about-update-and-backward-compatibility
• Docs/Readmes suggest installing compose-switch for translating docker-compose commands
• If you instead want to upgrade to v2 on Ubuntu and modify scripts: https://docs.docker.com/compose/cli-command/#install-on-linux

After the last Docker Desktop update, "docker-compose" automatically downgraded to v1.

Now there is a new option to select your "docker-compose" version, which was disabled by default:

Just to save people from insanity: Docker Desktop packaging appears to be glitchy.

I am running Docker Desktop 4.3.0 (71786) on Windows 11, with the WSL2 backend.

Here are the docker-compose information from my terminal:

% which docker-compose
/usr/bin/docker-compose
% ls -al /usr/bin/docker-compose
lrwxrwxrwx 1 root root 56 Dec   9 19:52 /usr/bin/docker-compose -> /mnt/wsl/docker-desktop/cli-tools/usr/bin/docker-compose
% sha256sum /usr/bin/docker-compose
35dd89af6820dc111991f4c9b8ed7b253fefa33a30392fed506490ddc2553e91 /usr/bin/docker-compose
% docker-compose --version
Docker Compose version v2.2.1

Docker Desktop has been freshly installed. With this version, _ is used as the separator character.

Now, let's switch to the same version of docker-compose, downloaded from GitHub:

% sudo wget -q https://github.com/docker/compose/releases/download/v2.2.1/docker-compose-linux-x86_64 -O /usr/local/bin/docker-compose-v2.2.1-gh
% sudo chmod 755 /usr/local/bin/docker-compose-v2.2.1-gh
% sudo ln -sf /usr/local/bin/docker-compose-v2.2.1-gh /usr/bin/docker-compose
% ls -al /usr/bin/docker-compose
lrwxrwxrwx 1 root root 39 Dec   9 20:18 /usr/bin/docker-compose -> /usr/local/bin/docker-compose-v2.2.1-gh
% sha256sum /usr/bin/docker-compose
68a3bb67bd25abf0f6da2a9d171a873ac182c3cc1c51fb4866e7770675823d2f  /usr/bin/docker-compose
% docker-compose --version
Docker Compose version v2.2.1

With the GitHub version, - is used as the separator character, as expected.

This means that Docker doesn't just repackage the binaries available on GitHub, but make their own builds from a source tree that is different from the one tagged with the same version on GitHub. (Thanks @tentative for pointing out the line of code defining the separator!)

And some final notes:

• docker-compose from other recent versions of Docker Desktop used - as expect.
• It is not the first time that switching between - and _ happened. Anecdotally, I remember having the very same issue a few months back, but after upgrading it went away.
• If you don't destroy your environment, docker-compose up will use the existing container names. This means that it may take you a while to notice the change.
• I have reported this to the GitHub Issue Tracker of Docker for Windows.

We noticed that the command

docker compose up and docker-compose up

would give either _ or - depending on which one you used.