I ditched Docker for Podman

I've been on Podman for about two years now. My coworkers and the entire company codebase / scripts etc are on Docker.

Podman has a number of caveats that make it not a drop in replacement out of the box, but they are mostly few and far between. Once you've learned to recognize a handful of common issues, it's quite simple to migrate.

This might sound like me trying to explain away some of the shortcomings of podman, but honestly, from my point of view, podman does it better, and the workarounds and fixes I make to our scripts and code for podman are backwards compatible and I view them as improvements.

Do you have a summary of those most common issues and their workarounds?

Broadly, the claim that Podman is a drop-in replacement for Docker is true only for the simple cases, but people have developed assorted dependencies on Docker implementation details. Examples:

1. People hear about how great rootless is with Podman but then expect to be able to switch directly from rootful Docker to rootless Podman without changing anything. The only way that could work is if there was no difference between rootful and rootless to begin with, but people don't want to hear that. They combine these two selling points in their head and think they can get both a drop-in replacement for Docker and also rootless by default. The proper choice is to either switch from rootful Docker to rootful Podman *or* put in the work to make your container work in rootless, work you would also have had to do with rootless Docker.

2. Docker Compose started out as an external third-party add-on (v1) which was later rewritten as an internal facility (v2) but `podman compose` calls out to either `docker-compose` (i.e. v1) or to its own clone of the same mechanism, `podman-compose`. The upshot is a lot of impedance mismatch. Combine that with the fact that Podman wants you to use Quadlets anyway, resulting in less incentive to work on these corner cases.

3. Docker has always tried to pretend SELinux doesn't exist, either by hosting on Debian and friends or by banging things into place by using their privileged (rootful) position. Podman comes from Red Hat, and until recently they had Mr SELinux on the team. Thus Podman is SELinux-first, all of which combines to confuse transplants who think they can go on ignoring SELinux.

4. On macOS and Windows, both Podman and Docker need a background Linux VM to provide the kernel, without which they cannot do LXC-type things. These VMs are not set up precisely the same way, which produces migration issues when someone is depending on exact details of the underlying VM. One common case is that they differ in how they handle file sharing with the host.

For #2, it will also use docker compose v2 if available. Docker compose v2 is still a standalone binary even in the case of installing Docker (it's a plugin). As long as you download the v2 binary, put it in the correct location, the podman compose subcommand will invoke it.