Alright, let’s dive into the world of multi-stage builds with NestJS. As a developer who’s been around the block a few times, I can tell you that optimizing your build process is like finding a secret shortcut on your daily commute – it might not seem like much at first, but boy, does it make a difference in the long run!
When I first started working with NestJS, I was blown away by its powerful features and modular architecture. But as my projects grew in complexity, I noticed that my build times were starting to creep up, and my Docker images were getting a bit… well, chunky. That’s when I discovered the magic of multi-stage builds.
Multi-stage builds are like a Marie Kondo approach to your Docker images – they help you keep only what sparks joy (or in this case, what’s absolutely necessary for your app to run). The basic idea is to use multiple stages in your Dockerfile, where each stage builds upon the previous one, but only carries forward what’s essential.
Let’s start with a simple example. Here’s what a basic Dockerfile for a NestJS app might look like:
FROM node:14
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
CMD ["npm", "run", "start:prod"]
This works, but it’s not very efficient. We’re carrying around all our dev dependencies and source code in the final image. Let’s see how we can improve this with a multi-stage build:
# Build stage
FROM node:14 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
# Production stage
FROM node:14-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
CMD ["node", "dist/main"]
Now we’re cooking with gas! This Dockerfile uses two stages: a build stage and a production stage. The build stage does all the heavy lifting – installing dependencies, copying the source code, and building the app. The production stage then copies only the built assets and production dependencies from the build stage.
The result? A much slimmer final image that contains only what’s needed to run your app in production. It’s like going from a bulky winter coat to a sleek windbreaker – you’re still protected from the elements, but you can move a lot faster!
But wait, there’s more! We can take this a step further by using a specific build image for NestJS. The NestJS CLI provides a nest build command that can create a standalone application, which can run without node_modules. Here’s how we can leverage that:
# Build stage
FROM node:14 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
RUN npm run build:prod
# Production stage
FROM node:14-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
CMD ["node", "dist/main"]
In this version, we’re using npm run build:prod (which you’d set up in your package.json to run nest build --webpack) to create a standalone application. This means our production stage doesn’t even need the node_modules directory!
Now, you might be thinking, “That’s all well and good, but what about my development workflow?” Great question! One of the things I love about multi-stage builds is that they play nicely with development environments too. You can use the same Dockerfile for both production and development by leveraging build arguments:
# Build stage
FROM node:14 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
# Development stage
FROM builder AS development
CMD ["npm", "run", "start:dev"]
# Production stage
FROM node:14-alpine AS production
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
CMD ["node", "dist/main"]
With this setup, you can build for development with docker build --target development -t myapp:dev . and for production with docker build --target production -t myapp:prod .. It’s like having your cake and eating it too!
But what about build time, you ask? Multi-stage builds can help there too. By leveraging Docker’s build cache effectively, you can significantly reduce build times for incremental changes. Here’s a pro tip: structure your Dockerfile to copy and install dependencies before copying your source code. This way, if your dependencies haven’t changed, Docker can use the cached layer:
FROM node:14 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
# Copy source code after installing dependencies
COPY . .
RUN npm run build
This simple change can shave minutes off your build time when you’re iterating quickly on your code.
Now, let’s talk about some real-world optimizations. In one project I worked on, we were dealing with a monorepo structure where our NestJS app was just one part of a larger ecosystem. We used Lerna to manage our packages, which added an extra layer of complexity to our builds.
To tackle this, we created a custom build script that only built the packages our NestJS app depended on, rather than building the entire monorepo. We then used this script in our Dockerfile:
FROM node:14 AS builder
WORKDIR /app
COPY package*.json ./
COPY lerna.json ./
RUN npm install
COPY . .
RUN npm run build:nest-app
# ... rest of the Dockerfile
This approach, combined with careful use of .dockerignore to exclude unnecessary files, cut our build times by almost 40%!
Another technique I’ve found useful is to use build arguments to control what gets included in the final image. For example, you might want to include some debugging tools in a staging environment but not in production. Here’s how you can do that:
ARG NODE_ENV=production
FROM node:14-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
RUN if [ "$NODE_ENV" = "staging" ] ; then npm install --only=production some-debug-tool ; fi
CMD ["node", "dist/main"]
You can then build your staging image with docker build --build-arg NODE_ENV=staging -t myapp:staging ..
One last tip: don’t forget about your npm scripts! They can be a powerful tool in your build optimization arsenal. For example, you might have a script that generates your API documentation. In development, you might want to regenerate this on every build, but for production, you could generate it once and copy it into your image:
FROM node:14 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
RUN npm run build
RUN npm run generate-docs
FROM node:14-alpine AS production
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY --from=builder /app/docs ./docs
CMD ["node", "dist/main"]
In conclusion, multi-stage builds in NestJS are like a Swiss Army knife for your Docker images – they help you create lean, mean, production-ready machines while still maintaining a flexible development environment. By carefully structuring your Dockerfile, leveraging build cache, and using techniques like build arguments and custom npm scripts, you can significantly reduce both your build times and final image sizes.
Remember, optimizing your build process is an ongoing journey. As your app evolves, so too should your build strategy. Keep experimenting, measuring, and refining. And most importantly, have fun with it! After all, there’s something deeply satisfying about watching those build times drop and image sizes shrink. Happy building!