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Select a container engine (Docker or Podman)

tailor runs Image Customizer in a container through the Docker Engine API. Podman speaks the same API, so tailor can use either — the engine is just a different socket.

Use Podman for the whole workspace

Set runtime.engine in tailor.yaml:

# tailor.yaml
runtime:
  engine: podman   # docker (default) | podman | auto

With engine: podman, tailor connects to Podman's default socket: the rootless socket $XDG_RUNTIME_DIR/podman/podman.sock when XDG_RUNTIME_DIR is set, otherwise the rootful /run/podman/podman.sock. Start the service first if it is not socket-activated:

systemctl --user start podman.socket   # rootless
# or, ad hoc:
podman system service --time=0 &

Use Podman for one build only

The global --engine flag overrides the manifest for a single invocation:

tailor --engine podman build app

Point at a specific socket or a remote engine

Use --host (or runtime.host) for a non-default endpoint:

tailor --host unix:///run/user/1000/podman/podman.sock build app
tailor --engine podman --host tcp://builder:2375 build app

--host takes a unix://… socket path (a bare /path works too) or a tcp://… endpoint.

Auto-detect

engine: auto (or --engine auto) probes the Docker socket (or DOCKER_HOST), then the rootless and rootful Podman sockets, and uses the first that answers:

tailor --engine auto build app

Precedence

Engine and endpoint resolve as two independent axes, each highest-first:

  • engine — --engine → runtime.engine → docker.
  • endpoint — --host → the engine's environment variable (DOCKER_HOST for docker, CONTAINER_HOST for podman) → runtime.host → the engine's default socket (or, for auto, the probe list).

--engine and --host are complementary: --engine chooses the daemon, --host chooses where it lives. A DOCKER_HOST set in the environment is ignored when the resolved engine is podman.

Fail fast

Before a build or clean starts, tailor pings the resolved engine and aborts immediately — before any image work — if it is missing or unreachable, naming the engine, the endpoint, and a fix:

$ tailor --engine podman --host unix:///nonexistent.sock build app
error: container runtime error: podman engine not found: no socket at /nonexistent.sock.
Start it with `systemctl --user start podman.socket` (rootless) or `podman system service`.

tailor build --dry-run never contacts an engine, so it works without a running daemon regardless of --engine / --host.

If you point --engine at an endpoint that is actually a different engine (for example --engine podman at a Docker socket), tailor uses the engine the socket really is and prints a warning — the live daemon is the source of truth.