Question: is Podman (Docker-compatible API) in scope for the Linux Docker backend?

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Evaluación

Dificultad
5/5
Tiempo estimado
Más de una semana
Aptitud para principiantes
25/100
Tipo de issue
Documentación
Claridad
Necesita aclaración
Estado de actividad
Activo
Stack tecnológico
docker, rust
Área
infrastructure

Línea de trabajo

This is a support-scope question rather than a concrete change, and it reports blockers in the Linux Docker backend at engine/crates/layerfs-sandbox/src/backend/docker/version.rs, backend/docker/topology.rs, and backend/docker/container.rs. First confirm whether Podman support is intended with the maintainers; only then decide whether platform notes should document support or exclusion. Done means an explicit answer and, if appropriate, documentation describing the supported configuration.

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Descripción

Hello, and thank you for LayerFS.

This is a question, not a request: is running the Linux Docker backend against Podman's Docker-compatible API socket something you want to support? I could not find an existing issue or a platform note about it (searched this repository for "podman", "rootless", "seccomp", "Engine API" and "1.48"), so I am asking before assuming anything.

What I tried

Rootless Podman 6.1.4 on x86_64 Linux (btrfs, /dev/fuse present), podman.socket enabled, LayerFS built from main (checked again at 67310175e). I used a static docker CLI client against the Podman socket, LAYERFS_DOCKER pointing at it, and @layerfs/runtime for Init.

What I measured

  1. The runtime shells out to docker (api/runtime/src/platform/shared.js), so a docker client binary has to be on PATH. That works with a static client; I list it only for completeness.
  2. Init as the ordinary user fails with the Store install runs as user 1000; it must run as user 0, the daemons' user. Under rootless Podman, container root maps to the host user, so the Store file is owned by that user; running Init inside podman unshare passes the check. I understand the check exists because the daemon (0:0) opens only a Store it owns.
  3. GET /version on Podman reports ApiVersion 1.44. The Sandbox backend (engine/crates/layerfs-sandbox/src/backend/docker/version.rs, OLDEST) refuses anything below 1.48 with Unsupported("Engine API version") before sending a request. The documentation gives the reason (Docker before 28 fails the daemon archive upload with getent unable to find entry "0:0"), which does not obviously apply to Podman. To see what comes next, I put a small forwarding proxy in front of the socket that only rewrites "ApiVersion":"1.44" to "1.48"; LayerFS itself was unchanged.
  4. With that, POST /containers/create fails with HTTP 500: {"cause":"file name too long","message":"container create: open {\"defaultAction\":\"SCMP_ACT_ALLOW\",.... HostConfig.SecurityOpt carries seccomp=<inline JSON> (SECCOMP in backend/docker/topology.rs, written by backend/docker/container.rs). Docker's Engine accepts the profile text there; Podman's compatibility API treats the value as a file path. As far as I can tell no single string works for both. I did not get past this point, so I do not know whether the container inspection check in topology.rs would accept Podman's answer.

Why I am not proposing to just relax these

Both the version gate and the inline seccomp profile look deliberate: the gate avoids a real failure on older Docker, and the profile blocks user namespaces so a command cannot copy a Workspace mount out of the daemon's namespace. I would not want to weaken either.

The question

Is Podman support in scope for the Docker backend, or would you rather point Podman users at one of the other Sandbox backends being consolidated for 2.0.0? If it is in scope, two directions seem possible, and I do not claim either is small:

  • Detect the engine from GET /version (Components) and use the form that engine accepts for the version check and for passing the seccomp profile.
  • Let the deployment pass the seccomp profile (inline text or a host path) through a setting instead of a constant.

If it is out of scope, a line in the platform notes saying so would help the next person who tries. Happy to share the proxy and logs if useful.

🤖 Generated with Claude Code

Lenguaje dominante
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