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Node.js + Docker for Showing Good Defaults in Using Node.js with Docker

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This tries to be a "good defaults" example of starting to use Node.js in Docker for local development and shipping to production with basic bells, whistles, and best practices. Issues/PR welcome.

Note I have more advanced examples of Node.js Dockerfiles and Compose files in my DockerCon 2022 talk and repository. I also have more about everything Docker and Node.js in my 8 hour video course Docker for Node.js.

Also Note, I have other resources on Docker and Kubernetes here.

Local Development Features

  • Dev as close to prod as you can. Docker Compose builds a local development image that is just like the production image except for the below dev-only features needed in the image. The goal is to have dev environment be as close to test and prod as possible while still giving all the nice tools to make you a happy dev.
  • Prevent needing node/npm on host. This installs node_modules outside app root in the container image so local development won't run into a problem of bind-mounting over it with local source code. This means it will run npm install once on container build and you don't need to run npm on host or on each docker run. It will re-run on build if you change package.json.
  • One line startup. Uses docker compose up for single-line build and run of local development server.
  • Edit locally while code runs in container. Docker Compose uses proper bind-mounts of host source code into container so you can edit locally while running code in Linux container.
  • Use nodemon in container. Docker Compose uses nodemon for development for auto-restarting Node.js in container when you change files on host.
  • Enable debug from host to container. Opens the inspect port 9229 for using host-based debugging like chrome tools or VS Code. Nodemon enables --inspect by default in Docker Compose.
  • Provides VSCode debug configs and tasks for tests. for Visual Studio Code fans, .vscode directory has the goods, thanks to @JPLemelin.
  • Small image and quick re-builds. COPY in package.json and run npm install before COPY in your source code. This saves big on build time and keeps the container image lean.
  • Bind-mount package.json. This allows adding packages in realtime without rebuilding images. e.g. docker compose exec -w /opt/node_app node npm install --save <package name>

Production-minded Features

  • Use Docker built-in healthchecks. This uses Dockerfile HEALTHCHECK with /healthz route to help Docker know if your container is running properly (example always returns 200, but you get the idea).
  • Proper NODE_ENV use. Defaults to NODE_ENV=production in Dockerfile and overrides to development in docker-compose for local dev.
  • Don't add dev dependencies into the production image. Proper NODE_ENV use means dev dependencies won't be installed in the image by default. Using Docker Compose will build with them by default.
  • Enables proper SIGTERM/SIGINT for graceful exit. Defaults to node index.js rather than npm for allowing graceful shutdown of node. npm doesn't pass SIGTERM/SIGINT properly (you can't ctrl-c when running docker run in foreground). To get node index.js to graceful exit, extra signal-catching code is needed. The Dockerfile and index.js document the options and links to known issues.
  • Run Node.js in the container as node user, not root.
  • Use docker-stack.yml example for Docker Swarm deployments.

Assumptions

  • You have Docker and Docker Compose installed (Docker Desktop for Mac/Windows/Linux).
  • You want to use Docker for local development (i.e. never need to install Node.js/npm on host) and have dev and prod Docker images be as close as possible.
  • You don't want to lose fidelity in your dev workflow. You want a easy environment setup, using local editors, Node.js debug/inspect, local code repository, while Node.js server runs in a container.
  • You use docker-compose for local development only (docker-compose was never intended to be a production deployment tool anyway).
  • The docker-compose.yml is not meant for docker stack deploy in Docker Swarm, it's meant for happy local development. Use docker-stack.yml for Swarm.

Getting Started

If this was your Node.js app, to start local development you would:

  • Running docker compose up is all you need. It will:
  • Build custom local image enabled for development (nodemon, NODE_ENV=development).
  • Start container from that image with ports 80 and 9229 open (on localhost).
  • Starts with nodemon to restart Node.js on file change in host pwd.
  • Mounts the pwd to the app dir in container.
  • If you need other services like databases, just add to compose file and they'll be added to the custom Docker network for this app on up.
  • Compose won't rebuild automatically, so either run docker compose build after changing package.json or do what I do and always run docker compose up --build.
  • Be sure to use docker compose down to cleanup after your done dev'ing.

If you wanted to add a package while docker-compose was running your app:

  • docker compose exec -w /opt/node_app node npm install --save <package name>
  • This installs it inside the running container.
  • Nodemon will detect the change and restart.
  • --save will add it to the package.json for next docker compose build

To execute the unit-tests, you would:

  • Execute docker compose exec node npm test, It will:
  • Run a process npm test in the container.
  • You can use the vscode to debug unit-tests with config Docker Test (Attach 9230 --inspect), It will:
    • Start a debugging process in the container and wait-for-debugger, this is done by vscode tasks
    • It will also kill a previous debugging process if existing.

Ways to improve security

Run Node.js as Non-Root User

As mentioned in the official docker Node.js image docs, Docker runs the image as root. This can pose a potential security issue.

As a security best practice, it is recommended for Node.js apps to listen on non-privileged ports as mentioned here.

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