The Raw Control Editor's Match Joints to Mesh (ML) operator runs Epic's nlstools ML matcher in an isolated Python 3.11 process. The addon ships two transports for that process, selectable in Edit ▸ Preferences ▸ Add-ons ▸ Character DNA ▸ NLS Worker Transport:

This page covers the Docker route.

Prerequisites

• A 64-bit x86 host. (The worker image only ships for linux/amd64.)
• Free disk space for the worker image (~300 MB after build).
• On Windows: Docker Desktop 4.x or newer with the WSL 2 backend enabled.
• On macOS: Docker Desktop 4.x or newer.
• On Linux: Docker Engine 24+ (or Docker Desktop for Linux).

Install

• Windows / macOS: download Docker Desktop from docker.com/products/docker-desktop and run the installer. Launch Docker Desktop once and wait for the whale icon in the system tray to report Docker Desktop is running.
• Linux: follow the distro instructions at docs.docker.com/engine/install. Make sure your user is in the docker group (sudo usermod -aG docker $USER, then log out + back in) so the addon can talk to the daemon without sudo.

Verify

Open a terminal and run:

docker version

You should see both a Client and a Server section. If the Server section is missing or reports an error, the daemon isn't running -- start Docker Desktop / the docker service and try again.

First Match Bones click

The first time you run Match Joints to Mesh (ML) with the Docker transport selected, the addon will:

1. Probe the Docker daemon (cached for 30 s thereafter).
2. Build the worker image character-dna-nls-worker:py311-v1 from the bundled Dockerfile. This downloads python:3.11-slim plus a handful of shared libraries and installs numpy==1.26.4 -- typically 30 -- 60 s on a warm broadband connection.
3. Spawn the container, bind-mount the extracted Linux NLS package read-only at /work/nls, bind-mount your ML model directory read-only at /work/models, and start the worker on a free local port.

Subsequent Match Bones clicks skip steps (2) and re-use the cached container for the rest of the Blender session. The container is labeled character_dna_worker=true so a stale instance (e.g. after a Blender crash) is automatically removed the next time you load the addon.

Switching back to System Python

Open Edit ▸ Preferences ▸ Add-ons ▸ Character DNA ▸ NLS Worker Transport and choose System Python. The dropdown is hidden on macOS because there are no native NLS binaries for darwin.

Troubleshooting

docker CLI not found on PATH. Install Docker Desktop / Engine and make sure the installer added the CLI to your shell's PATH. On Linux this is usually /usr/bin/docker.

Docker is installed but the daemon is not reachable. Start Docker Desktop or run sudo systemctl start docker.

Image build fails with a network error. Docker pulled the base image from Docker Hub; check your firewall / proxy settings. You can also pre-pull the base image with docker pull python:3.11-slim.

Linux NLS package missing. Click Extract Dependencies in the addon preferences. On Windows hosts extraction now lays down both the Windows and Linux trees so you can switch between transports without re-extracting.