tmpfs options are incompatible with type cluster

Error message

tmpfs options are incompatible with type cluster

What it means

Returned by handleClusterToMount (cli/compose/convert/volume.go:203-204). tmpfs options (size) describe an in-memory filesystem and are meaningless for a Swarm cluster volume, so the converter rejects a `tmpfs:` block on a cluster entry. (The handler accepts its own `cluster:` block and does not check `image:`; it explicitly forbids tmpfs, bind, and volume.)

Solutions

Delete the `tmpfs:` options block from the cluster entry.
If a size-capped in-memory filesystem was intended, change `type:` to `tmpfs` (no source).

Example fix

# before
volumes:
  - type: cluster
    source: my-cluster-vol
    target: /data
    tmpfs:
      size: 67108864

# after
volumes:
  - type: cluster
    source: my-cluster-vol
    target: /data

Defensive patterns

Strategy: validation

Validate before calling

for i, v := range serviceVolumes {
    if v.Type == "cluster" && v.Tmpfs != nil {
        return fmt.Errorf("service volume[%d] target=%q: type cluster must not declare a tmpfs block", i, v.Target)
    }
}

Try / catch

mounts, err := convert.Volumes(serviceVolumes, stackVolumes, namespace)
if err != nil && strings.Contains(err.Error(), "tmpfs options are incompatible with type cluster") {
    return fmt.Errorf("compose config error: %w (remove the tmpfs: block from the cluster entry)", err)
}

Prevention

Cluster volumes are persistent Swarm storage; tmpfs options never apply.
Strip tmpfs blocks when converting a tmpfs entry into a cluster volume.

When it happens

Trigger: ServiceVolumeConfig with Type=="cluster" and Tmpfs!=nil passed to convertVolumeToMount().

Common situations: Converting a tmpfs entry to a cluster volume without removing the `tmpfs:` block; YAML anchors merging tmpfs options.

Related errors

AI-assisted analysis of docker/cli@4f84911bfe (2026-08-07). Data as JSON: /api/errors/4ca9d2f6fa701630. Report an issue: GitHub.

Appendix: source

Thrown at cli/compose/convert/volume.go:204

	}
	if volume.Bind != nil {
		result.BindOptions = &mount.BindOptions{
			Propagation: mount.Propagation(volume.Bind.Propagation),
		}
	}
	return result, nil
}

func handleClusterToMount(
	volume composetypes.ServiceVolumeConfig,
	stackVolumes volumes,
	namespace Namespace,
) (mount.Mount, error) {
	if volume.Source == "" {
		return mount.Mount{}, errors.New("invalid cluster source, source cannot be empty")
	}
	if volume.Tmpfs != nil {
		return mount.Mount{}, errors.New("tmpfs options are incompatible with type cluster")
	}
	if volume.Bind != nil {
		return mount.Mount{}, errors.New("bind options are incompatible with type cluster")
	}
	if volume.Volume != nil {
		return mount.Mount{}, errors.New("volume options are incompatible with type cluster")
	}

	result := createMountFromVolume(volume)
	result.ClusterOptions = &mount.ClusterOptions{}

	if !strings.HasPrefix(volume.Source, "group:") {
		// if the volume is a cluster volume and the source is a volumegroup, we
		// will ignore checking to see if such a volume is defined. the volume
		// group isn't namespaced, and there's no simple way to indicate that
		// external volumes with a given group exist.
		stackVolume, exists := stackVolumes[volume.Source]
		if !exists {

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