DevContainer CLI Port Forwarder

Overview

This Python script dynamically forward ports from a host machine to a Docker container according to devcontainer.json forwardPorts.

This Python script is created because currently DevContainer CLI does not support port forwarding, see devcontainers/cli issue

Usage Context

This script is only needed if you are managing your containers directly with the devcontainer CLI.
If you are using vSCode with the Visual Studio Code Dev Containers extension,The VS Code extension already includes built-in support for port forwarding you do not need to use this script.

Prerequisites

host machine: Python 3 interpreter is installed.
container: socat is installed.

Features

Dynamic Port Forwarding: Automates the process of forwarding specified ports from the host to a Docker container.
Automatic Shutdown: The script automatically exits when the associated Docker container stops running.

Installation

git clone this project under your project's .devcontainer directory, or anywhere you like.

git clone https://github.com/nohzafk/devcontainer-cli-port-forwarder.git .devcontainer/devcontainer-cli-port-forwarder

This script won't automatically install socat inside the container for you, you need to install socat inside the container.

you can simply add a line in onCreateCommand in your devcontainer.json

"onCreateCommand": "sudo apt update && sudo apt install -y socat",

or use nix feature

"features": {
    "ghcr.io/devcontainers/features/nix:1": {
        "packages": "socat"
    }
},

Usage

In your devcontainer.json, set the initializeCommand to run the script in the background when the container is being initialized:

"initializeCommand": "python3 .devcontainer/devcontainer-cli-port-forwarder/forwarder.py &",

To enable verbose output, which provides more detailed information about the port forwarding process, modify the initializeCommand as follows:

"initializeCommand": "python3 .devcontainer/devcontainer-cli-port-forwarder/forwarder.py verbose &",

and finally specify the ports that you want to forward from host by forwardPorts,

for example port 2222 used by devcontainer feature sshd "ghcr.io/devcontainers/features/sshd:1": {},

Use 'forwardPorts' to make a list of ports inside the container available locally.

"forwardPorts": [2222],

Once configured in your devcontainer.json, the script will automatically start when you create a devcontainer using the devcontainer CLI. It listens on specified ports and forwards them to the Docker container.

The script runs in the background and does not require manual intervention once started.
When the Docker container stops, the script detects this and exits automatically, ensuring that resources are not left unnecessarily consumed on the host machine.

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