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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:/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.