Devcontainers Nix skill

Dev Containers & Nix Environments

Reproducible, portable development environments that eliminate environment drift.

When to Use This Skill

Use this skill when:

• Onboarding new developers (zero-to-productive in minutes)
• Standardizing toolchains across a team
• Eliminating "works on my machine" problems
• Setting up CI environments that match local dev
• Creating ephemeral, disposable dev environments

Dev Containers

Basic Configuration

// .devcontainer/devcontainer.json
{
  "name": "My Project",
  "image": "mcr.microsoft.com/devcontainers/base:ubuntu-22.04",
  "features": {
    "ghcr.io/devcontainers/features/node:1": { "version": "20" },
    "ghcr.io/devcontainers/features/python:1": { "version": "3.12" },
    "ghcr.io/devcontainers/features/docker-in-docker:2": {},
    "ghcr.io/devcontainers/features/kubectl-helm-minikube:1": {}
  },
  "forwardPorts": [3000, 5432],
  "postCreateCommand": "npm install",
  "customizations": {
    "vscode": {
      "extensions": [
        "dbaeumer.vscode-eslint",
        "esbenp.prettier-vscode",
        "ms-python.python"
      ],
      "settings": {
        "editor.formatOnSave": true
      }
    }
  }
}

Docker Compose Dev Container

// .devcontainer/devcontainer.json
{
  "name": "Full Stack Dev",
  "dockerComposeFile": "docker-compose.yml",
  "service": "app",
  "workspaceFolder": "/workspace",
  "forwardPorts": [3000, 5432, 6379],
  "postCreateCommand": "npm install && npx prisma migrate dev"
}

# .devcontainer/docker-compose.yml
services:
  app:
    build:
      context: ..
      dockerfile: .devcontainer/Dockerfile
    volumes:
      - ..:/workspace:cached
    command: sleep infinity
    depends_on: [db, redis]

  db:
    image: postgres:16
    environment:
      POSTGRES_DB: dev
      POSTGRES_USER: dev
      POSTGRES_PASSWORD: dev
    volumes:
      - pgdata:/var/lib/postgresql/data
    ports:
      - "5432:5432"

  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"

volumes:
  pgdata:

Custom Dockerfile

# .devcontainer/Dockerfile
FROM mcr.microsoft.com/devcontainers/base:ubuntu-22.04

# System dependencies
RUN apt-get update && apt-get install -y \
    build-essential \
    curl \
    git \
    jq \
    unzip \
    && rm -rf /var/lib/apt/lists/*

# Install project-specific tools
RUN curl -fsSL https://get.opentofu.org/install-opentofu.sh | sh -s -- --install-method standalone
RUN curl -LO "https://dl.k8s.io/release/$(curl -sL https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl" \
    && install kubectl /usr/local/bin/

# Non-root user setup
USER vscode
WORKDIR /workspace

Nix Flakes

Basic Flake

# flake.nix
{
  description = "Project development environment";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in {
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [
            # Languages
            nodejs_20
            python312
            go_1_22
            rustc
            cargo

            # Tools
            docker-compose
            kubectl
            kubernetes-helm
            opentofu
            awscli2
            jq
            yq-go

            # Databases
            postgresql_16
            redis
          ];

          shellHook = ''
            echo "Dev environment loaded"
            export PROJECT_ROOT=$(pwd)
            export PATH="$PROJECT_ROOT/node_modules/.bin:$PATH"
          '';
        };
      }
    );
}

# Enter the dev shell
nix develop

# Or run a single command
nix develop --command bash -c "node --version && go version"

# Build and run
nix build
nix run

Pin Dependencies

# Lock flake inputs for reproducibility
nix flake lock
nix flake update  # Update all inputs

# Update a specific input
nix flake lock --update-input nixpkgs

Devbox (Nix Made Simple)

Devbox wraps Nix with a friendlier interface:

# Install Devbox
curl -fsSL https://get.jetify.com/devbox | bash

# Initialize project
devbox init

# Add packages
devbox add nodejs@20 python@3.12 postgresql@16
devbox add go@1.22 kubectl helm

# Enter shell
devbox shell

# Run commands without entering shell
devbox run node --version

devbox.json Configuration

{
  "$schema": "https://raw.githubusercontent.com/jetify-com/devbox/main/.schema/devbox.schema.json",
  "packages": [
    "nodejs@20",
    "python@3.12",
    "go@1.22",
    "kubectl@1.29",
    "kubernetes-helm@3.14",
    "opentofu@1.8",
    "awscli2@2.15",
    "jq@1.7",
    "postgresql@16",
    "redis@7"
  ],
  "env": {
    "PROJECT_ROOT": "$PWD",
    "DATABASE_URL": "postgresql://localhost:5432/dev"
  },
  "shell": {
    "init_hook": [
      "echo 'Dev environment ready'",
      "npm install --silent 2>/dev/null || true"
    ],
    "scripts": {
      "dev": "npm run dev",
      "test": "npm test",
      "db:start": "pg_ctl -D .devbox/virtenv/postgresql/data start",
      "db:stop": "pg_ctl -D .devbox/virtenv/postgresql/data stop",
      "db:migrate": "npx prisma migrate dev"
    }
  }
}

# Run project scripts
devbox run dev
devbox run test
devbox run db:start

# Generate direnv integration (auto-activate on cd)
devbox generate direnv

# Generate Dockerfile from devbox config
devbox generate dockerfile

Devbox + direnv (Auto-Activate)

# Install direnv
devbox add direnv

# Generate .envrc
devbox generate direnv

# Allow direnv
direnv allow

# .envrc (auto-generated)
eval "$(devbox generate direnv --print-envrc)"

Now cd-ing into the project automatically loads the environment.

CI/CD Integration

GitHub Actions with Devbox

# .github/workflows/ci.yml
name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: jetify-com/devbox-install-action@v0.11.0
        with:
          enable-cache: true
      - run: devbox run test
      - run: devbox run lint

GitHub Actions with Nix

name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: cachix/install-nix-action@v26
        with:
          nix_path: nixpkgs=channel:nixos-unstable
      - uses: cachix/cachix-action@v14
        with:
          name: my-project
          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
      - run: nix develop --command bash -c "npm ci && npm test"

GitHub Codespaces

// .devcontainer/devcontainer.json — works in Codespaces
{
  "name": "Codespaces Dev",
  "image": "mcr.microsoft.com/devcontainers/universal:2",
  "features": {
    "ghcr.io/devcontainers/features/node:1": { "version": "20" }
  },
  "postCreateCommand": "npm install",
  "portsAttributes": {
    "3000": { "label": "App", "onAutoForward": "openBrowser" },
    "5432": { "label": "Postgres", "onAutoForward": "ignore" }
  }
}

Comparison

Feature	Dev Containers	Nix Flakes	Devbox
Learning curve	Low	High	Low
Reproducibility	Good (Docker)	Excellent	Excellent (Nix)
Speed	Slow (build image)	Fast (cached)	Fast (cached)
IDE support	VS Code, JetBrains	Any terminal	Any terminal
CI integration	Docker-based	Nix actions	Devbox action
Offline support	Limited	Full	Full
macOS/Linux/Win	All	macOS/Linux	macOS/Linux

Best Practices

• Pin all tool versions explicitly — never use latest
• Commit lock files (flake.lock, devbox.lock, etc.)
• Use direnv for automatic environment activation
• Cache Nix store in CI (Cachix or GitHub cache)
• Document setup in README: devbox shell or nix develop
• Keep dev environment close to production (same Node/Python versions)

Troubleshooting

Issue	Solution
Nix build slow first time	Use binary cache (Cachix), nix develop caches after first run
Dev Container won't build	Check Docker disk space, rebuild with --no-cache
Package not in Nixpkgs	Search at search.nixos.org, or use fetchFromGitHub overlay
Devbox hash mismatch	Run devbox update, delete .devbox/ and re-init
direnv not activating	Run direnv allow, check shell hook is installed

Related Skills

• docker-management — Container image optimization
• github-actions — CI/CD pipeline setup
• linux-administration — System-level tooling