Advanced devcontainer configuration

An atomic linux distribution

I recently tried a new linux distribution : Bluefin, it’s an atomic operating system based on Fedora Silverblue. The atomic nature forces you to use containers when doing development, since your root filesystem is locked. I like it because it forces good practices,containerizing everithing so your system stay stable.

Devcontainers

To help with the management of containers for application development Microsoft created the Development Container specification. There is a visual studio code extension that enables you to easily manage your configurations.

Adding extensions to the container environment

When VSCode remotes into a container or a machine the extensions needs to be installed on this remote. Whe can configure the DevContainer to have extensions preinstalled by setting customizations.vscode.extensions. Here is an example for my Dendron setup :

{
	"name": "Dendron",
	"build": {
		"dockerfile": "Dockerfile"
	},
	"remoteUser": "node",
	"customizations": {
		"vscode": {
		"extensions": [
			"dendron.dendron",
			"dendron.dendron-markdown-shortcuts",
			"dendron.dendron-paste-image",
			"redhat.vscode-yaml"
			]
		}
	}
}

Putting the configuration outside of the project’s directory

By default the devcontainer configuration is placed in the project’s directory, in .devcontainer/devcontainer.json. If you don’t have control over the project this can be a problem as you need to avoid commiting this configuration in the repository. The devcontainer extension offers a solution : when creating a new devcontainer configuration with ctrl+shift+p > Dev Containers: Reopen in Container it asks you where you want to put the configuration, either in the “user data folder” or in the workspace (the project’s directory). Selecting the firt option places the configuration in a folder in ~/.config/Code/User/globalStorage/ms-vscode-remote.remote-containers/configs/.

If you want to use a custom dockerfile you can also place it in this folder and reference it in the configuration, the path is relative to the devcontainer.json file.

{
	"name": "Rust",
	"build": {
		// Path is relative to the devcontainer.json file.
		"dockerfile": "Dockerfile"
	}
}

Using FUSE in a Dev Container

FUSE (Filesystem in Userspace) allows a program to setup a virtual file system without adding a module to the Kernel. It doesn’t work by defauld in a container and needs access to some ressources of the host system. You can easily configure the devcontainer to allow that :

{
	"name": "Rust",
	"build": {
		"dockerfile": "Dockerfile"
	},
	"capAdd": [
		"SYS_ADMIN"
	],
	"runArgs": [
		"--security-opt",
		"apparmor:unconfined",
		"--device",
		"/dev/fuse"
	]
}

You also need to customize the container image to include the fuse executable, here’s my Dockerfile for my rust project :

FROM mcr.microsoft.com/devcontainers/rust:1-bookworm
RUN apt update && apt upgrade -y
RUN apt install -y fuse3