Recently, I noticed that the Docker image size for my Next.js project was quite large. So I decided to do some research and found ways to reduce the image size.

Baseline

Here’s what my initial Dockerfile looked like:

FROM node:18
WORKDIR /app
COPY . .
RUN yarn install
RUN yarn build
EXPOSE 3000
CMD ["yarn", "start"]

It ended up being around 3GB.

Step 1: Use a Smaller Base Image

Before making any changes, my Docker image was using the standard Node.js base image. To reduce the image size, I switched to the Alpine Linux version. Here’s the updated Dockerfile with a smaller base image:

FROM node:18-alpine
WORKDIR /app
COPY . .
RUN yarn install
RUN yarn build
EXPOSE 3000
CMD ["yarn", "start"]

This switch reduced the image size by 1GB, a significant improvement.

Step 2: Use Multi-Stage Build

The next optimization was using a multi-stage build. This allowed me to separate the build process and include only the necessary files in the final image.

FROM node:18-alpine AS builder
WORKDIR /app
COPY ./package.json ./
RUN yarn install
COPY . .
RUN yarn build

FROM node:18-alpine AS runner
WORKDIR /app
COPY --from=builder /app/.next ./.next
COPY --from=builder /app/public ./public
COPY --from=builder /app/package.json ./
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node_modules/.bin/next", "start"]

Using multi-stage builds reduced the image size from 2GB to 520MB.

Step 3: Next.js Output Configuration

To optimize the size even further, I updated the next.config.js file to generate a standalone build.

// next.config.js
/** @type {import('next').NextConfig} */
module.exports = {
  output: "standalone",
};

To use standalone build, I updated my Dockerfile:

FROM node:18-alpine AS builder
WORKDIR /app
COPY ./package.json ./
RUN yarn install
COPY . .
RUN yarn build

FROM node:18-alpine AS runner
WORKDIR /app
COPY --from=builder /app/.next/standalone ./
COPY --from=builder /app/.next/static ./.next/static
EXPOSE 3000
ENV PORT=3000
ENV HOSTNAME="0.0.0.0"
CMD ["node", "server.js"]

This configuration, helped keep the Dockerfile image size around 146MB.

Conclusion

Through these optimizations, I was able to reduce the Docker image size from 3GB to 146MB. This not only makes the image faster to build and deploy but also saves storage.

References

1. Official Docker Documentation
2. Next.js Output Configuration
3. Optimizing Docker Image Sizes