Devcontainers Nix Agent Skill

Create reproducible development environments with Dev Containers, Nix flakes, and Devbox for consistent toolchains across teams. Use when onboarding developers, standardizing build environments, or eliminating "works on my machine" problems.

2k tokens

context cost

the whole folder, loaded on every use

files

instructions only

copies elsewhere

how many repositories repackaged it

511

stars on the repo

on the repository, not the skill itself

Install

one command, takes just this skill from the repository

npx skills add https://github.com/BagelHole/DevOps-Security-Agent-Skills --skill devcontainers-nix

The instruction itself

20 sections, as written by the author

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 [email protected] postgresql@16
devbox add [email protected] kubectl helm

# Enter shell
devbox shell

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

devbox.json Configuration

{
  "$schema": "https://raw.githubusercontent.com/jetify-com/devbox/main/.schema/devbox.schema.json",
  "packages": [
    "nodejs@20",
    "[email protected]",
    "[email protected]",
    "[email protected]",
    "[email protected]",
    "[email protected]",
    "[email protected]",
    "[email protected]",
    "postgresql@16",
    "redis@7"
  ],
  "env": {
    "PROJECT_ROOT": "$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/[email protected]
        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

|---------|---------------|------------|--------|

| Learning curve | Low | High | Low |

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 |

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

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How to use it

Copy the folder

Take bagelhole/devcontainers-nix from the repository into ~/.claude/skills for personal use, or into .claude/skills inside a project.

Check the name does not clash

The agent identifies a skill by the name field in its header. Two skills with the same name cannot sit side by side — one of them will be ignored.

Install what it needs

The instructions reference npm, npx, apt. Without those the skill loads but fails at the first command.

Devcontainers Nix Agent Skill

Install

The instruction itself

Dev Containers & Nix Environments

When to Use This Skill

Dev Containers

Basic Configuration

Docker Compose Dev Container

Custom Dockerfile

Nix Flakes

Basic Flake

Pin Dependencies

Devbox (Nix Made Simple)

devbox.json Configuration

Devbox + direnv (Auto-Activate)

CI/CD Integration

GitHub Actions with Devbox

GitHub Actions with Nix

GitHub Codespaces

Comparison

Best Practices

Troubleshooting

Related Skills

Other skills for the same job

How to use it