🐳 Docker over SSH

The solver runs inside a Docker container on a remote Linux host, managed by a Docker daemon reached through SSH. Two UI modes cover the two ways to provide SSH credentials: Custom (explicit fields) and Command (parsed from a raw ssh ... string).

Where each piece lives, and how the add-on reaches it. Blue solid arrows carry lifecycle commands (container start/stop, exec, port check). Purple dashed arrows carry the TCP connection to ppf-cts-server, which rides an SSH tunnel into the container’s published port on the remote’s localhost. For the local variant where the daemon and container run on the Blender machine, see Docker (Local).

When to Use It

• A GPU host runs Docker for you and you reach it over SSH.

• Your cluster administrator hands you a container instead of shell access on the bare host.

• Multiple solvers share one remote GPU host and you want each project isolated.

Setup - Custom Mode

The SSH fields from the SSH (Direct) page are combined with the Docker fields: the add-on opens an SSH session to the remote host and runs every Docker command there.

1. Set Type to Docker over SSH.

2. Fill Host / Port / User / SSH Key as in SSH Custom mode – these locate the remote host that runs the Docker daemon. Fill Proxy Jump as well if that host is only reachable through a bastion (see Jump Hosts).

3. Fill Container with the container name on the remote daemon (the field defaults to ppf-contact-solver). The add-on runs docker exec against this name over the SSH session.

4. Fill Container Path with the working directory inside that container (e.g. /root/ppf-contact-solver). This path is not interpreted on the Blender host or on the remote host’s filesystem – it is the path seen from inside the container, where the ppf-cts-server binary lives.

5. Set Docker Port to the TCP port ppf-cts-server listens on inside the container.

6. Click Connect. The add-on verifies that the container exists on the remote host and starts it if it is stopped.

Backend Communicator with Type set to Docker over SSH Command. The SSH Command field replaces the per-field SSH inputs (in Custom mode you would see Host / Port / User / SSH Key instead). Container, Container Path, and Docker Port are the same fields as in Docker (Local). Connect is highlighted.

Field	Description
Container	Container name on the remote Docker daemon. Must already exist.
Container Path	Working directory inside the remote container that holds the ppf-cts-server binary.
Docker Port	Port inside the container where ppf-cts-server listens. Must be published on the container with -p.

Warning

The server port must be published on the container (-p 9090:9090 or equivalent in your compose file). Before Start Server on Remote, the add-on checks the port mapping on the remote host and refuses to continue if the port is not exposed – the error text tells you exactly which port and container failed. You must fix this on the container side; the add-on cannot publish ports on a container that is already created.

Setup - Command Mode

Identical to Custom Mode, but the SSH parameters come from a pasted command instead of separate fields.

1. Set Type to Docker over SSH Command.

2. Paste the SSH command into SSH Command, e.g. ssh -p 2222 -i ~/.ssh/gpu_key alice@gpu01.example.com. See the SSH Command section for the parser rules.

3. Fill Container with the container name on the remote daemon (the same field as in Custom Mode – it is not parsed from the command string).

4. Fill Container Path with the working directory inside that container (where the ppf-cts-server binary lives). This is also a separate field and is never derived from the SSH command.

5. Set Docker Port and click Connect.

The Container and Container Path fields behave exactly as in Custom Mode – only the host / port / user / key path are sourced from the pasted command.

Installing paramiko

Docker over SSH needs the paramiko Python package only: the remote daemon is driven by docker commands run over the SSH session, not by docker-py. The main panel shows an Install Paramiko to Add-on Directory button when it is missing, which installs into Blender’s user scripts/addons/modules directory.

Troubleshooting

• Container 'X' does not exist. - the name is wrong or the container was removed on the remote. Run docker ps -a on the remote to see what is actually there.

• Error starting container 'X' - the daemon returned a non-zero exit or the remote user lacks docker group membership.

• Server startup timed out. - the container started but ppf-cts-server did not become ready within 16 seconds. Check server.log inside the directory set in Container Path; the panel prints the last 20 lines automatically.

Under the hood

Transport

An SSH session is opened to the remote host and every Docker command is wrapped in docker exec -w <cwd> <container> ... on that session. During connect the add-on checks that the container exists and starts it if it is stopped; a missing container aborts the connect.

Port publication check

Before Start Server on Remote the add-on runs

docker port <container> <port>

on the remote SSH host. A non-zero exit code aborts with:

Docker port 9090 is not exposed on container ‘ppf-contact-solver’. Please expose the port with ‘-p 9090:9090’ when starting the container.

Fix this on the container side by re-running docker run -p 9090:9090 (or editing your compose.yaml); the add-on cannot publish ports on an existing container.

Server startup path

Docker over SSH uses the same Unix server-launch path as the SSH and Local backends (see Connections - Under the hood): a small script inside the container launches ppf-cts-server on the configured port and the UI waits up to 16 s for readiness.