Dockerfile Generator

new-dockerfile is a CLI tool and Go package automatically generates a configurable Dockerfile based on your project source code. It supports a wide range of languages and frameworks, including Next.js, Node.js, Python, Ruby, Java/Spring Boot, Go, Elixir/Phoenix, and more.

See the FlexStack Documentation page for FlexStack-specific documentation related to this tool.

Features

• Automatically detect the runtime and framework used by your project
• Use version managers like asdf, nvm, rbenv, and pyenv to install the correct version of the runtime
• Make a best effort to detect any install, build, and start commands
• Generate a Dockerfile with sensible defaults that are configurable via Docker Build Args
• Support for a wide range of the most popular languages and frameworks including Next.js, Phoenix, Spring Boot, Django, and more
• Use Debian Slim as the runtime image for a smaller image size and better security, while still supporting the most common dependencies and avoiding deployment headaches caused by Alpine Linux gotchas
• Includes wget in the runtime image for adding health checks to services, e.g. wget -nv -t1 --spider 'http://localhost:8080/healthz' || exit 1
• Includes ca-certificates in the runtime image to allow secure HTTPS connections
• Use multi-stage builds to reduce the size of the final image
• Run the application as a non-root user for better security
• Supports multi-platform images that run on both x86 and ARM CPU architectures

Supported Runtimes

• Bun
• Deno
• Elixir
• Go
• Java
• Next.js
• Node.js
• PHP
• Python
• Ruby
• Rust
• Static (HTML, CSS, JS)

Additional runtimes we'd like to support

• C#/.NET
• C++
• Scala
• Zig

Consider contributing to add support for these or any other runtimes!

Installation

cURL

curl -fsSL https://flexstack.com/install/new-dockerfile | bash

Go Package

go get github.com/flexstack/new-dockerfile

CLI Usage

new-dockerfile [options]

CLI Options

• --path - Path to the project source code (default: .)
• --write - Write the generated Dockerfile to the project at the specified path (default: false)
• --runtime - Force a specific runtime, e.g. node (default: auto)
• --quiet - Disable all logging except for errors (default: false)
• --help - Show help

CLI Examples

Print the generated Dockerfile to the console:

new-dockerfile

Write a Dockerfile to the current directory:

new-dockerfile --write

Write a Dockerfile to a specific directory:

new-dockerfile > path/to/Dockerfile

Force a specific runtime:

new-dockerfile --runtime next.js

List the supported runtimes:

new-dockerfile --runtime list

Read from Config file

In the CI use case, you might need a very common step for generating a Dockerfile. You can create a config file for the CLI options. The default config file name is new-dockerfile.yaml, and it should be in the root directory of your git repository. Especially, there are multiple kinds of files, new-dockerfile might not be able to it a correct one.

runtime: go

And, the CLI option will overwrite the values from config file.

How it Works

The tool searches for common files and directories in your project to determine the runtime and framework. For example, if it finds a package.json file, it will assume the project is a Node.js project unless a next.config.js file is present, in which case it will assume the project is a Next.js project.

From there, it will read any .tool-versions or other version manager files to determine the correct version of the runtime to install. It will then make a best effort to detect any install, build, and start commands. For example, a serve, start, start:prod command in a package.json file will be used as the start command.

Runtimes are matched against in the order they appear when you run new-dockerfile --runtime list.

Read on to see runtime-specific examples and how to configure the generated Dockerfile.

Runtime Documentation

Bun

Bun is a fast JavaScript all-in-one toolkit

Detected Files

• bun.lockb
• bun.lock
• bunfig.toml

Version Detection

• .tool-versions - bun {VERSION}
• .mise.toml - bun = "{VERSION}"

Runtime Image

oven/bun:${VERSION}-slim

Build Args

• VERSION - The version of Bun to install (default: 1)
• INSTALL_CMD - The command to install dependencies (default: bun install)
• BUILD_CMD - The command to build the project (default: detected from package.json)
• START_CMD - The command to start the project (default: detected from package.json)

Build Command

Detected in order of precedence:

• package.json scripts: "build:prod", "build:production", "build-prod", "build-production", "build"

Start Command

Detected in order of precedence:

• package.json scripts: "serve", "start:prod", "start:production", "start-prod", "start-production", "preview", "start"
• package.json main/module file: bun run ${mainFile}

---

Deno

Deno is a secure runtime for JavaScript with native TypeScript and JSX support

Detected Files

• deno.jsonc
• deno.json
• deno.lock
• deps.ts
• mod.ts

Version Detection

• .tool-versions - deno {VERSION}
• .mise.toml - deno = "{VERSION}"

Runtime Image

debian:stable-slim

Build Args

• VERSION - The version of Deno to install (default: latest)
• INSTALL_CMD - The command to install dependencies (default: detected from deno.jsonc and source code)
• START_CMD - The command to start the project (default: detected from deno.jsonc and source code)

Install Command

Detected in order of precedence:

• deno.jsonc tasks: "cache"
• Main/module file: deno cache ["mod.ts", "src/mod.ts", "main.ts", "src/main.ts", "index.ts", "src/index.ts]"

Start Command

Detected in order of precedence:

• deno.jsonc tasks: "serve", "start:prod", "start:production", "start-prod", "start-production", "preview", "start"
• Main/module file: deno run ["mod.ts", "src/mod.ts", "main.ts", "src/main.ts", "index.ts", "src/index.ts]"

---

Elixir

Elixir is a dynamic, functional language designed for building scalable and maintainable applications.

Detected Files

• mix.exs

Version Detection

• .tool-versions - elixir {VERSION}
• .tool-versions - erlang {VERSION}
• .elixir-version - {VERSION}
• .erlang-version - {VERSION}
• .mise.toml - erlang = "{VERSION}"

Runtime Image

debian:stable-slim

Build Args

• VERSION - The version of Elixir to install (default: 1.12)
• OTP_VERSION - The version of Erlang to install (default: 26.2.5)
• BIN_NAME - The name of the release binary (default: detected via app name in mix.exs)

Start Command

/app/bin/{BIN_NAME} start

---

Go

Go is an open-source programming language that makes it easy to build simple, reliable, and efficient software.

Detected Files

• go.mod
• main.go

Version Detection

• .tool-versions - golang {VERSION}
• .mise.toml - go = "{VERSION}"
• go.mod - go {VERSION}

Runtime Image

debian:stable-slim

Build Args

• VERSION - The version of Go to install (default: 1.17)
• TARGETOS - The target OS for the build (default: linux)
• TARGETARCH - The target architecture for the build (default: amd64)
• CGO_ENABLED - Enable CGO for the build (default: 0)
• GOPROXY - The Go module proxy to use (default: direct)
• PACKAGE - The package to compile e.g. ./cmd/http (default: detected via cmd directory or main.go)

Package Detection

• Find the directory in cmd with a .go file
• main.go file in the root directory

Install Command

if [ -f go.mod ]; then go mod download; fi

Build Command

CGO_ENABLED=${CGO_ENABLED} GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -trimpath -ldflags="-s -w" -o /go/bin/app "${PACKAGE}"

Start Command

["/app/app"]

---

Java

Java is a class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible.

Detected Files

• pom.{xml,atom,clj,groovy,rb,scala,yml,yaml}

Version Detection

JDK version:

• .tool-versions - java {VERSION} Maven version:
• .tool-versions - maven {VERSION}

Runtime Image

eclipse-temurin:${VERSION}-jdk

Build Args

• VERSION - The version of the JDK to install (default: 17)
• MAVEN_VERSION - The version of Maven to install (default: 3)
• JAVA_OPTS - The Java options to pass to the JVM (default: -Xmx512m -Xms256m)
• BUILD_CMD - The command to build the project (default: best guess via source code)
• START_CMD - The command to start the project (default: detected via source code)

Install Command

• If Maven: mvn install

Build Command

• If Maven: mvn -DoutputFile=target/mvn-dependency-list.log -B -DskipTests clean dependency:list install

Start Command

• Default: java $JAVA_OPTS -jar target/*jar
• If Spring Boot: java -Dserver.port=${PORT} $JAVA_OPTS -jar target/*jar

---

Next.js

Next.js is a React framework that enables functionality such as server-side rendering and generating static websites.

Detected Files

• next.config.{js,mjs,cjs,ts,mts}
• next-env.d.ts
• .next/

Version Detection

• .tool-versions - nodejs {VERSION}
• .nvmrc - v{VERSION}
• .node-version - v{VERSION}
• .mise.toml - node = "{VERSION}"
• package.json - "engines": {"node": "{VERSION}"}

Runtime Image

node:${VERSION}-slim

Build Args

• VERSION - The version of Node.js to install (default: lts)

Install Command

if [ -f yarn.lock ]; then yarn --frozen-lockfile; \
elif [ -f package-lock.json ]; then npm ci; \
elif [ -f bun.lockb ]; then npm i -g bun && bun install; \
elif [ -f pnpm-lock.yaml ]; then corepack enable pnpm && pnpm i --frozen-lockfile; \
else echo "Lockfile not found." && exit 1; \
fi

Build Command

if [ -f yarn.lock ]; then yarn run build; \
elif [ -f package-lock.json ]; then npm run build; \
elif [ -f bun.lockb ]; then npm i -g bun && bun run build; \
elif [ -f pnpm-lock.yaml ]; then corepack enable pnpm && pnpm run build; \
else echo "Lockfile not found." && exit 1; \
fi

Start Command

• If "output" :"standalone" in next.config.js: HOSTNAME="0.0.0.0" node server.js
• Otherwise ["node_modules/.bin/next", "start", "-H", "0.0.0.0"]

---

Node.js

Node.js is a JavaScript runtime built on Chrome's V8 JavaScript engine.

Detected Files

• yarn.lock
• package-lock.json
• pnpm-lock.yaml

Version Detection

• .tool-versions - nodejs {VERSION}
• .nvmrc - v{VERSION}
• .node-version - v{VERSION}

Runtime Image

node:${VERSION}-slim

Build Args

• VERSION - The version of Node.js to install (default: lts)
• INSTALL_CMD - The command to install dependencies (default: detected from source code)
• BUILD_CMD - The command to build the project (default: detected from source code)
• START_CMD - The command to start the project (default: detected from source code)

Install Command

• If Yarn: yarn --frozen-lockfile
• If npm: npm ci
• If pnpm: corepack enable pnpm && pnpm i --frozen-lockfile

Build Command

In order of precedence:

• package.json scripts: "build:prod", "build:production", "build-prod", "build-production", "build"

Start Command

In order of precedence:

• package.json scripts: "serve", "start:prod", "start:production", "start-prod", "start-production", "preview", "start"
• package.json scripts search for regex matching: ^.*?\b(ts-)?node(mon)?\b.*?(index|main|server|client)\.([cm]?[tj]s)\b
• package.json main/module file: node ${mainFile}

---

PHP

PHP is a popular general-purpose scripting language that is especially suited to web development.

Detected Files

• composer.json
• index.php

Version Detection

• .tool-versions - php {VERSION}
• composer.json - "php": "{VERSION}"

Runtime Image

php:${VERSION}-apache

Build Args

• VERSION - The version of PHP to install (default: 8.3)
• INSTALL_CMD - The command to install dependencies (default: detected via source code)
• BUILD_CMD - The command to build the project (default: detected via source code)
• START_CMD - The command to start the project (default: apache2-foreground)

Install Command

• If Composer: composer update && composer install --prefer-dist --no-dev --optimize-autoloader --no-interaction
• If package.json exists: composer install command + see Node.js install command

Build Command

• If package.json exists: see Node.js build command

Start Command

apache2-foreground

---

Python

Python is a high-level, interpreted programming language that is known for its readability and simplicity.

Detected Files

• requirements.txt
• uv.lock
• poetry.lock
• Pipefile.lock
• pyproject.toml
• pdm.lock
• main.py
• app.py
• application.py
• app/__init__.py
• filepath.Join(filepath.Base(path), "app.py")
• filepath.Join(filepath.Base(path), "application.py")
• filepath.Join(filepath.Base(path), "main.py")
• filepath.Join(filepath.Base(path), "__init__.py")

Version Detection

• .tool-versions - python {VERSION}
• .python-version - {VERSION}
• .mise.toml - python = "{VERSION}"
• runtime.txt - python-{VERSION}

Runtime Image

python:${VERSION}-slim

Build Args

• VERSION - The version of Python to install (default: 3.10)
• INSTALL_CMD - The command to install dependencies (default: detected from source code)
• START_CMD - The command to start the project (default: detected from source code)

Install Command

• If Poetry: pip install poetry && poetry install --no-dev --no-ansi --no-root
• If Pipenv: pipenv install --dev --system --deploy
• If uv: pip install uv && uv sync --python-preference=only-system --no-cache --no-dev
• If PDM: pip install pdm && pdm install --prod
• If pyproject.toml exists: pip install --upgrade build setuptools && pip install .
• If requirements.txt exists: pip install -r requirements.txt

Start Command

• If Django is detected: python manage.py runserver 0.0.0.0:${PORT}
• If FastAPI is detected: fastapi run [main.py, app.py, application.py, app/main.py, app/application.py, app/__init__.py] --port ${PORT}
• If pyproject.toml exists: python -m ${projectName}
• Otherwise: python [main.py, app.py, application.py, app/main.py, app/application.py, app/__init__.py]

---

Ruby

Ruby is a dynamic, open-source programming language with a focus on simplicity and productivity.

Detected Files

• Gemfile
• Gemfile.lock
• config.ru
• Rakefile
• config/environment.rb

Version Detection

• .tool-versions - ruby {VERSION}
• .ruby-version - {VERSION}
• .mise.toml - ruby = "{VERSION}"
• Gemfile - ruby '{VERSION}'

Runtime Image

ruby:${VERSION}-slim

Build Args

• VERSION - The version of Ruby to install (default: 3.0)
• INSTALL_CMD - The command to install dependencies (default: detected from source code)
• BUILD_CMD - The command to build the project (default: detected from source code)
• START_CMD - The command to start the project (default: detected from source code)

Install Command

• bundle install
• If package.json exists: bundle install && [package manager install command]

Build Command

• If Rails: bundle exec rake assets:precompile

Start Command

• If Rails: bundle exec rails server -b 0.0.0.0 -p ${PORT}
• If config.ru exists: bundle exec rackup config.ru -p ${PORT}
• If config/environment.rb exists: bundle exec rails server -b
• If Rakefile exists: bundle exec rake

---

Rust

Rust is a systems programming language that is known for its speed, memory safety, and parallelism.

Detected Files

• Cargo.toml

Runtime Image

debian:stable-slim

Build Args

• TARGETOS - The target OS for the build (default: linux)
• TARGETARCH - The target architecture for the build (default: amd64)
• BIN_NAME - The name of the release binary (default: detected via Cargo.toml)

Build Command

if [ "${TARGETARCH}" = "amd64" ]; then rustup target add x86_64-unknown-linux-gnu; else rustup target add aarch64-unknown-linux-gnu; fi
if [ "${TARGETARCH}" = "amd64" ]; then cargo zigbuild --release --target x86_64-unknown-linux-gnu; else cargo zigbuild --release --target aarch64-unknown-linux-gnu; fi

Start Command

Determined by the binary name in the Cargo.toml file

• ["/app/app"]

---

Static (HTML, CSS, JS)

Static Web Server is a cross-platform, high-performance & asynchronous web server for static files serving. It is nearly as fast as Nginx and Lighttpd, but is easily configurable with environment variables.

Detected Files

• public/
• static/
• dist/
• index.html

Runtime Image

joseluisq/static-web-server:${VERSION}-debian

Build Args

• VERSION - The version of the static web server to install (default: 2)
• SERVER_ROOT - The root directory of the server (default: detected from source code)

---

Used By

• FlexStack - A platform that simplifies the deployment of containerized applications to AWS. FlexStack uses this tool to automatically detect the runtime and framework used by your project, so you can just bring your code and deploy it with confidence.
• Your project here - If you're using this tool in your project, let us know! We'd love to feature you here.

Contributing

Read the CONTRIBUTING.md guide to learn how to contribute to this project.

License

This project is licensed under the MIT License - see the LICENSE file for details.