What are Multi-Stage Docker Images?
Tags: docker, tutorial, webdev, devops
Published: 2023-06-20 14:18:43

## Introduction

### Let's start from the basics

**Docker**! It's an awesome tool that lets you create, deploy, and run applications in these neat little containers. Think of them like tiny virtual machines, but with just enough resources to run your app. It's fantastic since it means you can run your application on any platform, *from your laptop to the cloud!*

### The Power of Docker Images

Docker images are one of the key elements that make Docker so powerful. These are pre-built, pre-configured packages that include everything your app requires to execute - code, libraries, and dependencies. They're like the ultimate Lego set for developing and distributing applications!

### But what if Docker images got better?

That's where multi-stage Docker images come in. They're like the superheroes of the Docker world - able to create smaller, faster, and more efficient images by separating the build and runtime environment. With multi-stage Docker images, you can save disk space, reduce build times, and even improve security!

## The Magic of Multi-Stage Docker Images

### What are Multi-Stage Docker Images?

Are you tired of creating bloated Docker images that take forever to build and deploy? Multi-stage Docker images to the rescue! These superheroes of the Docker world allow you to create smaller, faster, and more secure images by separating the build and runtime environment.  
Let's say you're building a TypeScript app with Node.js as the runtime environment. With a traditional Docker image, you'd have to include everything in the same image, leading to a larger image size. But with a multi-stage Docker image, you can create a lean and mean image that only includes what's necessary.

```bash
# First stage: build environment
FROM node:14-alpine as build
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Second stage: runtime environment
FROM node:14-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY package*.json ./
RUN npm install --only=production
CMD ["npm", "start"]
```

## Traditional vs. Multi-Stage Docker Images

Traditional Docker images use a single stage to build and package an application, which means that the image includes both the build and runtime environment. This can make the image larger and less efficient.  
On the other hand, multi-stage Docker images allow you to create smaller, more efficient images by separating the build and runtime environment. Each stage in a multi-stage Docker image can have its own base image, dependencies, and build instructions. You can use the COPY command to copy files between stages, and the final stage is used to create the final image that will be deployed.

Let's consider the above example of a Typescript app that you want to deploy to a serverless platform like AWS Lambda. With traditional Docker images, you would include both the build and runtime environment in a single image, which would result in a larger image size. This can slow down deployment times and make your app less responsive. Here's an example Dockerfile for a TypeScript app with traditional images:

```bash
# Tradional Docker image
FROM node:14-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install 
COPY . .
RUN npm run build
CMD ["npm", "start"]
```

As you can see, we not only install all dependencies, regardless of whether they are required in the production environment, but we also have the TypeScript code and the transpiled JavaScript, thus producing two copies of the same code.

Whereas with multi-stage Docker images, you can keep the size of your Docker image small by separating the build and runtime environment into separate stages. Here's an example Dockerfile for a TypeScript app that uses multi-stage Docker images:

```bash
# Build stage
FROM node:14 AS build
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build

# Runtime stage
FROM node:14-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY package*.json ./
RUN npm install --only=production
CMD [ "npm", "run", "start" ]
```

## Demystifying Multi-Stage Docker Images

Multi-stage Docker images work like a well-coordinated team, with each stage performing a specific task. In the first stage, you can use a TypeScript base image and include your source code and build tools. This stage compiles your TypeScript code and creates a build artifact.

```bash
FROM node:14 AS build
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
```

In the next stage, you can use a Node.js base image and copy only the runtime dependencies needed to run your app from the previous stage. By keeping the runtime environment separate, you can create a smaller, more efficient Docker image.

```bash
FROM node:14-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY package*.json ./
RUN npm install --only=production
CMD [ "npm", "run", "start" ]
```

The final stage can then create the final image that's ready for deployment. And the best part? With this approach, you can significantly reduce the size of your Docker image, making it faster and easier to deploy your TypeScript app.

## Conclusion

### Benefits of Multi-Stage Docker Images

They offer numerous benefits, including smaller image sizes, faster builds, reduced attack surface, and improved maintainability. By separating the build and runtime environments, you can create leaner, more efficient Docker images that are perfect for containerizing your applications.

### Final Thoughts

Multi-stage Docker images are particularly useful for applications with complex build processes or large dependencies, such as TypeScript applications. They also shine when deploying to serverless platforms like AWS Lambda or Kubernetes Clusters for easy and fast management.

### Further reading and learning

If you're interested in learning more about using Docker with TypeScript, check out my blog post "[Using TypeScript with Docker: A Guide to Containerize Your Applications](https://dev.to/hunt092/using-typescript-with-docker-a-guide-to-containerize-your-applications-4m9d)" *shameless plug*. This comprehensive guide covers everything from setting up a Docker environment to deploying your containerized TypeScript app. Additionally, the Docker documentation and online tutorials offer plenty of resources for further learning.

So, what are you waiting for? Begin using multi-stage Docker images to optimize your applications immediately! Don't forget to like and follow my blog to discover much more.