Autogenerate a Dockerfile

No Dockerfile? Unsure how to write one? With FlexStack, you bring the code and we can handle the rest.

When you deploy a GitHub repo to FlexStack, you don't explicitly need a Dockerfile. If we don't detect one in your repository, we'll attempt to generate one for you automatically based on your project's source code. This will work perfectly for the vast majority of cases, but if you find yourself needing more customization you may bring your own Dockerfile.

How it works

We search for common files and directories in your project to determine the runtime and framework you're using. For example, if we find a package-lock.json file, we 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, we will detect any .tool-versions or other version manager files to determine the correct version of the runtime to install. Then, we 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.

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

Customizing the generated Dockerfiles

All of the Dockerfiles we generate have Docker Build Arguments that make them configurable from the FlexStack dashboard. To do so, visit the Build tab in your FlexStack component.

A screenshot of the FlexStack dashboard's Build tab

If you need more customization, we suggest downloading our new-dockerfile CLI tool and using it directly within your project.

Features

  • Automatically detects the runtime and framework used by your project
  • Uses version managers like asdf, nvm, rbenv, and pyenv to install the correct version of the runtime
  • Makes a best effort to detect any install, build, and start commands
  • Generates a Dockerfile with sensible defaults that are configurable via Docker Build Args
  • Supports a wide range of the most popular languages and frameworks including Next.js, Phoenix, Spring Boot, Django, and more
  • Uses 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
  • Uses multi-stage builds to reduce the size of the final image
  • Runs 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!

Alternatives for generating Dockerfiles

  • new-dockerfile - Our CLI tool used for generating Dockerfiles from your project source code
  • @flyio/dockerfile - A tool for generating Dockerfiles for Node.js code

Runtime Documentation

Bun

Bun is a fast JavaScript all-in-one toolkit

Detected Files

  • bun.lockb
  • bunfig.toml

Version Detection

  • .tool-versions - 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}

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}

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}
  • 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

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

Version Detection

JDK version:

  • .tool-versions - java {VERSION} Gradle version:
  • .tool-versions - gradle {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)
  • GRADLE_VERSION - The version of Gradle to install (default: 8)
  • 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
  • If Gradle: ./gradlew clean build -x check -x test

Start Command

  • Default: java $JAVA_OPTS -jar target/*jar
  • If Gradle: java $JAVA_OPTS -jar $(ls -1 build/libs/*jar | grep -v plain)
  • If Spring Boot: java -Dserver.port=${PORT} $JAVA_OPTS -jar target/*jar
  • If Spring Boot w/ Gradle: java -Dserver.port=${PORT} $JAVA_OPTS -jar $(ls -1 build/libs/*jar | grep -v plain)

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}

Runtime Image

node:${VERSION}-slim

Build Args

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

Install Command

RUN 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

RUN 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
  • 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}
  • 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: poetry install --no-dev --no-interactive --no-ansi
  • If Pipenv: PIPENV_VENV_IN_PROJECT=1 pipenv install --deploy
  • If 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 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}
  • 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

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