Container Compendium

Here is your high-density field manual for the core Docker terminology and Node.js containerization workflow we covered in this lesson.

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Syntax Chart

Syntax	Purpose	Example
FROM	Defines the base image foundation	FROM node:20-alpine
WORKDIR	Sets the internal execution directory	WORKDIR /app
COPY	Copies files from the host to the image	COPY package*.json ./
RUN	Executes a command during the build	RUN npm install
EXPOSE	Documents the expected internal port	EXPOSE 3000
CMD	Defines the default runtime command	CMD ["npm", "start"]
docker build	Constructs the image from the recipe	docker build -t app-name .
docker run	Starts a container from an image	docker run -p 8080:3000 app-name
-p flag	Maps host port to container port	-p 8080:3000

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The Cargo Manifest

The required baseline pieces to package a standard Node.js application:

• Dockerfile: The exact recipe used at the root of the project to build the image.
• .dockerignore: Prevents local files (especially node_modules and .env) from bleeding into the image.
• package.json: Must include a valid start script for the CMD instruction to trigger.
• Docker Engine: Must be running locally on your machine to build or execute containers.

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The Hazard Map

Problem	Likely Cause	Quick Fix
Build is incredibly slow	Incorrect instruction order invalidating cache	Move COPY package*.json ./ and RUN npm install before COPY . .
Strange Node module errors	Host node_modules were copied into the Linux image	Add node_modules to your .dockerignore file
Container exits instantly	The default CMD process failed or finished immediately	Check package.json for a missing or crashing start script
”Cannot connect” in browser	Traffic isn’t crossing from the host into the container	Verify you used -p hostPort:containerPort (e.g. -p 3000:3000)
Build fails immediately	Docker can’t find the build context	Ensure you included the trailing . in the docker build -t name . command

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Solo’s Pro-Notes

• Images vs Containers: You build static images. You run live containers. An image is the class; a container is the object.
• Documentation only: EXPOSE does absolutely nothing operational by itself. It’s a sticky note for other developers. You must manually map the ports when running.
• Cache invalidation: A change to line X in a Dockerfile invalidates the cache for line X and every single line below it.
• Local Dev vs Containers: Don’t rely on your laptop’s invisible configuration. Push your requirements into the Dockerfile so the app is self-sufficient.

Pack it Right

Consistency is the goal. When you ship the environment alongside the code, you strip away an entire category of stressful deployment errors.

Immutability Rule

If you ever find yourself “logging into” a running container to manually fix a configuration file, you have failed the test. Fix the Dockerfile and rebuild the image.

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Extra Bits & Bytes

Docker Fundamentals Study Guide

Complete Node Aboard Demo GitHub Repo