Posted 12/07/2025Updated 02/15/20266 minutes read (About 889 words)

Build a remote Docker server that allows SSH connections

Background

There appears to be lots of screen recordings that occupy gigabytes of storage space locally on an MBP, which need to be compressed. While the local tasks running on an MBP may cause the heat dissipating fan to roaring, making use of an idle desktop seems a viable solution to accelerate the workflow.

Considerations Before Starting

Q: Why not refer to powerful cloud-top computing resources such as those on AWS/GCP/Azure?
A: Extra costs will apply, yet the deploying, debugging and tuning operations can’t be skipped still. On the contrary, a personal desktop as the server host is likely more cost-effective and easily maintainable for personal use cases versus in production.
Q: Why not use a U-disk to transfer the files from the MBP to the desktop device?
A: The source files are gigabytes of videos that can’t fit into the U-disk given the capacity limit.
Q: Why not establish a simple web service on the host over HTTP for a user-friendly interface?
A: Those web UI features (see also Docker API documentation) are more than necessary to achieve the goal. In the meantime, exposing the port 2375 (reference) over HTTP is not secured, yet the HTTPS/TLS setup via port 2376 introduced lots of complexity even when following the Docker’s documentation.

Quick Start

Counter-intuitively, there’s actually no need to install or run Docker Desktop app on either the client or server side, as long as the Docker daemon is ready on the server host and Docker CLI is present on the client side, saving lots of confusion, time and effort on the unnecessary desktop app settings.

Either Docker daemon and Docker CLI can be installed on the common *nix OS or distros including MacOS. If on Windows, Windows Subsystem Linux (WSL) will be helpful to prepare the runtime environment without the need to reinstall the entire OS or run a virtual machine, by enabling the certain optional feature instead.

Even if Docker Desktop is installed on Windows, the runtime environment has to be held in WSL anyway.

Server-side setup in Linux/WSL distro of Ubuntu (as an example)

Package sources

Common practice to refresh the list of available packages and their versions:

1	sudo apt update

Additionally, set up Docker’s apt repository using Docker’s official GPG key and Apt sources (recommended; see also Install Docker Engine on Ubuntu).

# Add Docker's official GPG key:
sudo apt update
sudo apt install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc

# Add the repository to Apt sources:
sudo tee /etc/apt/sources.list.d/docker.sources <<EOF
Types: deb
URIs: https://download.docker.com/linux/ubuntu
Suites: $(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}")
Components: stable
Signed-By: /etc/apt/keyrings/docker.asc
EOF

sudo apt update

Where is ifconfig?

After updating, install the net-tools package, which contains ifconfig, using this command:
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sudo apt install net-tools

OpenSSH server

1	sudo apt install openssh-server ssh-askpass ufw

Enable, Start and check SSH Service:

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sudo systemctl enable ssh
sudo systemctl start ssh
sudo systemctl status ssh

Adjust Firewall (using UFW):

1	sudo ufw allow ssh

Docker engine, daemon and container management (latest version)
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sudo apt install docker-ce docker-ce-cli containerd.io
The Docker service starts automatically after installation. To verify that Docker is running, use:
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sudo systemctl status docker
Verify that the installation is successful by running the hello-world image (expecting some human-readable self-explanatory outputs):
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sudo docker run hello-world
More usages about Docker daemon (read more)

Test Docker daemon connection in a debug mode:
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dockerd --debug
[--tls=true \]
[--tlscert=/var/docker/server.pem \]
[--tlskey=/var/docker/serverkey.pem \]
[--host tcp://192.168.59.3:2376]
By default the daemon stores data in:
- /var/lib/docker on Linux
- C:\ProgramData\docker on Windows

Cliend-side setup (reference)

Docker CLI needs to be installed on the client side as well, same as above.

Create a Docker context to specify a non-local Docker host:

docker context create \
    --docker host=ssh://docker-user@host1.example.com \
    --description="Remote engine" \
    my-remote-engine

The context doesn’t take effect immediately upon creation. The next step is to inform the Docker CLI to use it, and to connect to the remote engine:

1	docker context use my-remote-engine

Quickly test if the context works out:

1	docker info

Details

Additional SSH usages

Executing a simple command:

1	ssh user@example.com "ls -l /home/user"

Windows environment setup (skip this if not using Windows on a host)

Before digging deeper, beware of the difference between the concepts of WSL and WSL distros (read more).

What’s more, the current versions of WSL are 2.x, also referred to as WSL2. And the WSL command line tool will run in 2.x version by default.

WSL Distros

List all the distro versions ready to install
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wsl --list --online
List the local distros installed
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wsl --list [--verbose]
Install a specific distro (e.g. Ubuntu)
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wsl --install ubuntu
Start a WSL distro instance - simply run wsl in the built-in Command Prompt, Terminal App or Powershell.
Check for the private IP address assigned to the Distro, which is helpful for the upcoming network configs
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wsl hostname -I
Stop a running WSL distro only without removing its filesystem

As an example, it will make the changes to the .wslconfig file take effect:
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wsl --shutdown
Remove a WSL distro instance with its filesystem
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wsl --unregister ubuntu
Export a WSL distro to a file

It helps to create a backup (as .tar file by default) or relocate the distro to a different directory (shutdown recommended as above):
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wsl --export <DistributionName> <Full path to .tar/.vhdx FileName> [--vhd]
Import a file as a WSL distro

This allows to create a distro filesystem in a different directory other than before:
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wsl --import <NewDistributionName> <InstallLocation> <Full path to .tar/.vhdx FileName>

Network Configs on a Windows host

Allow for incoming ping requests

Add this rule to the firewall via Powershell with administrator permissions to resolve the timeout error of ping:
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New-NetFirewallRule -Name "Ping" -Protocol ICMPv4 -Direction Inbound -Action Allow

Allow for incoming SSH requests

This is to enable the built-in firewall rule for the OpenSSH Server:

1	Enable-NetFirewallRule -DisplayGroup "OpenSSH Server"

Alternatively, manually create a new inbound firewall rule:

1	New-NetFirewallRule -DisplayName "Allow SSH Inbound" -Direction Inbound -Protocol TCP -LocalPort 22 -Action Allow -Profile Any

Set up Port Forwarding on Windows host

This is to add a port proxy rule to forward a local port 22 on Windows host to the WSL SSH server port 22 in WSL:
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netsh interface portproxy add v4tov4 listenport=22 listenaddress=0.0.0.0 connectport=22 connectaddress=<wsl-ip>
Test connecting to WSL server via SSH from another device
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ssh username@host_ip [-p 22]
Alternative: SSH Tunnels from Windows to a Remote Host via WSL (SSH Tunneling)

This option hasn’t been tested and verified yet:
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ssh -L <local-port>:localhost:<remote-port> <remote-host>

Miscallaneous

Known Issues of WSL

Why does WSL end, and the established SSH connection get closed, after a while of being idle?

The cause lies in the WSL Idle Timeout setting. By default, WSL 2 goes into a suspended state (after a short period) once all open terminal windows and running processes have exited. The best way to prevent this is to configure the vmIdleTimeout setting in a Windows configuration file.

Navigate to the Windows user profile directory: %userprofile% (e.g., C:\Users\YourUsername).
Create a file named .wslconfig if it doesn’t exist.
Open the file and add the following lines:
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[wsl2]
; Sets the time in seconds that a WSL 2 distro can be idle before it is terminated.
; To disable the timeout, set this to -1.
vmIdleTimeout=-1

Known Issue of OpenSSH / Docker

docker stderr=ssh_askpass: exec(/usr/bin/ssh-askpass): No such file or director

External reference

Install the ssh-askpass package:
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sudo apt install [-y] ssh-askpass
“Connection timeout” even with SSH connection tested okay

Check docker context on both host and client sides:

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docker context ls
docker context show
docker context use [context name]