docker-portmap-client

This is a 🐳 Docker image you can use to expose one or more TCP ports to the internet using an SSH tunnel.

It works by connecting to a (publicly exposed) SSH server; this can be for example an instance of the dmotte/portmap-server image, or an online SSH tunneling service such as portmap.io or ngrok.com.

Note: this image runs as an unprivileged user (non-root).

📦 This image is also on Docker Hub as dmotte/portmap-client and runs on several architectures (e.g. amd64, arm64, ...). To see the full list of supported platforms, please refer to the .github/workflows/main.yml file. If you need an architecture which is currently unsupported, feel free to open an issue.

Usage

For this section, we assume that you have already set up an SSH server for remote port forwarding (such as dmotte/portmap-server) or you use an online port forwarding service.

This Docker image only supports SSH public key authentication, so we assume that you have a 🔑 private key file (hereinafter called ssh_client_key) to log in to the server. Please note that the private key file must be kept unencrypted, as otherwise the SSH client would ask for the passphrase at startup. Plus, it must be readable by the portmap unprivileged user inside the container.

Then you'll need an SSH known_hosts file containing the public fingerprint of your server. To obtain it, you can use the following command (replace the server address and port with yours):

ssh-keyscan -p2222 10.0.2.15 > known_hosts

Note: if you want, you can bypass the known_hosts step by adding -o StrictHostKeyChecking=no to the SSH command, but it's highly discouraged for security reasons. Please refer to the OpenSSH client manual page for further information.

Now suppose that you want to publicly expose (using portmap.io) a web service running locally in your LAN at http://192.168.0.123:8080/. You can start your portmap client container like this:

docker run -it --rm \
    -v "$PWD/known_hosts:/known_hosts:ro" \
    -v "$PWD/ssh_client_key:/ssh_client_key:ro" \
    dmotte/portmap-client \
    myuser.mycfg@myuser-12345.portmap.io -NvR12345:192.168.0.123:8080

For a more complex example, refer to the docker-compose.yml file.

Environment variables

List of supported environment variables:

Variable	Required	Description
KEEPALIVE_INTERVAL	No (default: 30)	Value for the ServerAliveInterval option of the OpenSSH client

Volumes

Internal path	Required	Description
/known_hosts	No	File containing the SSH server's public fingerprint(s)
/ssh_client_key	Yes	Unencrypted private key file that will be used by the OpenSSH client to authenticate itself. It must be readable by the portmap user inside the container

Development

If you want to contribute to this project, you can use the following one-liner to rebuild the image and bring up the Docker-Compose stack every time you make a change to the code:

docker-compose down && docker-compose up --build