How do I write a Dockerfile for a Node.js app?

Copy package.json and the lock file first and run npm ci, so Docker can reuse that layer when only source files change. Then copy the rest, run the build, set a non-root user, EXPOSE the port and start the app with CMD. The generator writes those lines in that order for Node.js, starting from FROM node:24-alpine; change the tag if your app targets another supported Node.js line.

Why is the syntax line the first line?

Docker reads a parser directive such as # syntax=docker/dockerfile:1.7 only at the top of the file. Once a comment, a blank line or an instruction has been read, a later directive is treated as an ordinary comment, so the generator puts it first.

How does it write environment variables with spaces or a dollar sign?

A value with a space, a quote or a backslash is wrapped in double quotes, so my value becomes ENV APP_MODE="my value". A dollar sign is escaped, because Docker expands $name in ENV values, so the text $5 stays $5. One variable is one line, and several use continuation lines with no continuation after the last.

What is the difference between the exec and shell form of CMD?

A start command written as a JSON array, such as ["node", "server.js"], becomes the exec form and runs the program directly. Any other text becomes the shell form, which the generator wraps in /bin/sh -c on Alpine images and bash -c on others. Docker recommends the exec form, because the shell form does not pass signals such as SIGTERM to the program.

Does the Dockerfile run as root?

By default it adds a user called app with UID 1001 and switches to it, for every language except static HTML. The nginx image starts as root and binds port 80, so non-root is off for it by default and can still be ticked. A user name keeps only letters, digits, dot, dash and underscore.

Does the page check that the Dockerfile builds?

No. It writes the file from your form and removes line breaks and control characters from every value, with a warning that lists what it removed. It does not run Docker, so build the image and read the output before you rely on the file.

Dockerfile Generator

Generate a Dockerfile from a form: pick a language, base image, ports, env vars, build and start commands, then copy or download the file. How it works

Preset:

Language

Base imageUse a custom base image...

Working directory

Listening ports

3000

Environment variables (ENV)

Build-time variables (ARG)

Install command

Build command

Start command (exec form or shell)

Multi-stage buildRun as non-root

User name

User UID

Dockerfile · node

1# syntax=docker/dockerfile:1.72# Generated by CalcChef Dockerfile Generator — YYYY-MM-DD3# Tip: add a .dockerignore with at least: node_modules, .git, .env, dist, build, target, __pycache__4 5FROM node:24-alpine6WORKDIR /app7 8COPY package*.json ./9RUN npm ci10 11COPY . .12RUN npm run build13 14# Run as non-root15RUN addgroup -S app && adduser -S app -G app -u 1001 \16 && chown -R app:app /app17USER app18 19# Listening ports20EXPOSE 300021 22CMD ["node", "server.js"]

Estimated size: ≈ 50–180 MB (alpine)

About the Dockerfile Generator

The default settings give a Dockerfile for a Node.js app that starts with # syntax=docker/dockerfile:1.7, then FROM node:24-alpine, WORKDIR /app, COPY package*.json ./, RUN npm ci, COPY . ., RUN npm run build, a non-root user, EXPOSE 3000 and a CMD that runs node server.js. Node.js 24 is the long-term-support line that endoflife.date listed on 16 October 2026, with security fixes until 30 April 2028. Check the tag against that list again before you build, because support dates move on. The file is text only: nothing has been built or checked against Docker.

What each language preset starts with

Language	Base image	Install command	Port	Multi-stage by default
Node.js	node:24-alpine	npm ci	3000	no
Python	python:3.12-slim	pip install --no-cache-dir -r requirements.txt	5000	no
Go	golang:1.27-alpine	go mod download	8080	yes
Java	eclipse-temurin:21-jre-alpine	mvn -B -e -DskipTests dependency:go-offline	8080	yes
.NET	mcr.microsoft.com/dotnet/aspnet:10.0	dotnet restore	8080	yes
Ruby	ruby:3.3-alpine	bundle install --jobs 4 --retry 3	4567	no
PHP	php:8.3-cli-alpine	composer install --no-dev --no-scripts --prefer-dist	8000	no
Rust	rust:1-slim	none	8080	yes
Static HTML	nginx:1.30-alpine	none	80	no

Read from the generator's own language defaults. They are starting values for you to change, not recommendations, and the tags were checked on 16 October 2026 against endoflife.date and nginx.org: Node.js 24 (long-term support), Go 1.27, .NET 10 (long-term support) and nginx 1.30 (the stable line). Python 3.12, Ruby 3.3, PHP 8.3 and Java 21 were still supported and are unchanged. The start commands assume a layout: Python runs app.py, Ruby runs app.rb on Sinatra's port 4567, and PHP runs php artisan serve, which only exists in a Laravel project. Java builds in a Maven image (with multi-stage off, that image is the only stage), and the build copies the first jar in target/ that is not a sources, javadoc or tests jar to app.jar. Rust has no install step, because cargo needs the source as well as Cargo.toml, and its build copies target/release/app, so the binary must be named app. PHP copies the Composer binary and installs unzip, installs without running scripts before the source is copied, and dumps the optimized autoloader after it. Its start command listens on 0.0.0.0, because artisan serve listens only inside the container by default.

How to use this tool

Pick a project preset or a language, then a base image from the list or your own image:tag. Check that the tag is still supported: the defaults were checked on 16 October 2026.
Set the working directory, ports, environment variables, build arguments, and the install, build and start commands.
Choose multi-stage and a non-root user if you want them. Read any warning above the file.
Press Copy or Download, then build the image yourself to check it.

Frequently asked questions

How do I write a Dockerfile for a Node.js app?: Copy package.json and the lock file first and run npm ci, so Docker can reuse that layer when only source files change. Then copy the rest, run the build, set a non-root user, EXPOSE the port and start the app with CMD. The generator writes those lines in that order for Node.js, starting from FROM node:24-alpine; change the tag if your app targets another supported Node.js line.
Why is the syntax line the first line?: Docker reads a parser directive such as # syntax=docker/dockerfile:1.7 only at the top of the file. Once a comment, a blank line or an instruction has been read, a later directive is treated as an ordinary comment, so the generator puts it first.
How does it write environment variables with spaces or a dollar sign?: A value with a space, a quote or a backslash is wrapped in double quotes, so my value becomes ENV APP_MODE="my value". A dollar sign is escaped, because Docker expands $name in ENV values, so the text $5 stays $5. One variable is one line, and several use continuation lines with no continuation after the last.
What is the difference between the exec and shell form of CMD?: A start command written as a JSON array, such as ["node", "server.js"], becomes the exec form and runs the program directly. Any other text becomes the shell form, which the generator wraps in /bin/sh -c on Alpine images and bash -c on others. Docker recommends the exec form, because the shell form does not pass signals such as SIGTERM to the program.
Does the Dockerfile run as root?: By default it adds a user called app with UID 1001 and switches to it, for every language except static HTML. The nginx image starts as root and binds port 80, so non-root is off for it by default and can still be ticked. A user name keeps only letters, digits, dot, dash and underscore.
Does the page check that the Dockerfile builds?: No. It writes the file from your form and removes line breaks and control characters from every value, with a warning that lists what it removed. It does not run Docker, so build the image and read the output before you rely on the file.

Important limitations

The image lists have not kept up with releases: the Node.js, Go, .NET and nginx tags they offer are past or near the end of support, so type a current tag as a custom base image. The multi-stage Go and Rust files use the full build image for the runtime stage as well, so they are larger than a slim runtime image would be, and a multi-stage Python file installs its requirements twice. The size line is a rough range for the image variant (Alpine, slim, full), not a measurement. EXPOSE documents a port but does not publish it.

Sources

Last reviewed: 2026-10-16

Starting a Dockerfile for a new project

Get a first Dockerfile for an app that has none yet. Pick Node.js, Python, Go, Java, .NET, Ruby, PHP, Rust, static HTML on nginx or a custom base, set the port, environment variables, and the install, build and start commands, then choose multi-stage or a non-root user.

It checks nothing against Docker, so build the file and read the output before you ship it. Line breaks and control characters are removed from every value you type, so one value cannot add a new instruction, and the page lists what it removed. Your edits are saved in this browser until you press Clear Saved Values; link values apply to that visit only, and your first edit after a language link saves that language's settings.

What the file contains

The generator joins fixed lines in order: the # syntax=docker/dockerfile:1.7 directive, a comment with the date the file was made, a comment suggesting a .dockerignore, then FROM, WORKDIR, ENV and ARG, a COPY of the dependency manifest with the install command (so Docker can reuse that layer when only source code changes), COPY . ., the build command, an optional non-root user, EXPOSE and CMD.

Example: the default Node.js settings give FROM node:24-alpine, WORKDIR /app, COPY package*.json ./, RUN npm ci, COPY . ., RUN npm run build, a user app with UID 1001, EXPOSE 3000 and a CMD that runs node server.js. Node.js 24 was a long-term-support line on endoflife.date on 16 October 2026; check the tag again before you ship.

An ENV value with a space, a quote or a backslash is wrapped in double quotes, and $ is escaped so Docker keeps it as text instead of expanding it. A start command that is a JSON array becomes the exec form of CMD. Any other text becomes the shell form, run through /bin/sh -c on Alpine images and bash -c on others. EXPOSE only documents a port; publishing it still needs -p when you run the container.

Related Tools

View all tools

Dev

HTTP Headers Viewer

See the request headers an echo service (httpbin.org) receives from one fetch by this page, or by your own URL. Copy as cURL, fetch(), Python or .env.

Dev

Random Data Generator

Generate 1 to 1,000 fake people as JSON, CSV or a SQL INSERT: id, name, email, phone, address, age and active, each optional but id. Seeds repeat rows.

Dev

User Agent Parser

Paste a User-Agent string to read the browser, engine, OS and version, device type and model, CPU hints or the crawler it names, with notes on frozen values.

Dev

SQL Query Formatter

Format SQL for Standard SQL, PostgreSQL, MySQL, SQLite or SQL Server, with keywords kept, upper-cased or lower-cased and 2-space, 4-space or tab indents.

Dev

Subnet Mask Cheat Sheet

Subnet mask table for every IPv4 prefix from /0 to /32: dotted mask, wildcard, total and usable hosts, with /31 counted as 2 (RFC 3021) and /32 as 1.

Dev

IP Address Viewer

See the public IP address your connection uses, with the approximate city, region, country and provider from ipapi.co, or look up any IPv4 or IPv6 address.