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How to Reduce Node Docker Image Size by 10X

July 03, 2020

Dockerizing an application is simple, effective, but optimizing the size of Docker Image is the tricky part. Docker is easy to use but once the application starts scaling, the image size inflates exponentially. In general, the node docker image size of the applications is over 1 GB most of the time.

Why the Size matters

  1. Large docker image sizes - Bigger image size requires more space means increased expense.
  2. Long build durations - It takes a longer time to push the images over the network and results in CI Pipeline delays.

Let’s Start The Optimization

Here is our demo application built using the VueJS Application.

Here is the initial Dockerfile.

FROM node:10

WORKDIR /app

COPY . /app

EXPOSE 8080

RUN npm install http-server -g

RUN npm install && npm run build

CMD http-server ./dist

The size of this image is:

docker1

It is 1.34GB! Whoops!

Let’s start optimizing step by step

  1. Use Multi-Stage Docker Builds

Multi-stage builds make it easy to optimize Docker images by using multiple intermediate images in a single Dockerfile. Read more about it here. By using multi-stage builds, we can install all dependencies in the build image and copy them to the leaner runtime image.

FROM node:10 AS BUILD_IMAGE

WORKDIR /app

COPY . /app

EXPOSE 8080

RUN npm install && npm run build

FROM node:10

WORKDIR /app

# copy from build image
COPY --from=BUILD_IMAGE /app/dist ./dist
COPY --from=BUILD_IMAGE /app/node_modules ./node_modules

RUN npm i -g http-server

CMD http-server ./dist

Now the size of this image is 1.24GB:

docker2

  1. Remove Development Dependencies and use Node Prune Tool

node-prune is an open-source tool for removing unnecessary files from the node_modules folder. Test files, markdown files, typing files and *.map files in Npm packages are not required at all in the production environment generally, most of the developers do not remove them from the production package. By using node-prune it can safely be removed.

We can use this to remove Development Dependencies:

npm prune --production

After making these changes Dockerfile will look like:

FROM node:10 AS BUILD_IMAGE

RUN curl -sfL https://install.goreleaser.com/github.com/tj/node-prune.sh | bash -s -- -b /usr/local/bin

WORKDIR /app

COPY . /app

EXPOSE 8080

RUN npm install && npm run build

# remove development dependencies
RUN npm prune --production

# run node prune
RUN /usr/local/bin/node-prune

FROM node:10

WORKDIR /app

# copy from build image
COPY --from=BUILD_IMAGE /app/dist ./dist
COPY --from=BUILD_IMAGE /app/node_modules ./node_modules

RUN npm i -g http-server

CMD http-server ./dist

By using this we reduced the overall size to 1.09GB

docker3

  1. Choose Smaller Final Base Image

When dockerizing a node application, there are lots of base images available to choose from.

Here we will use alpine image; alpine is a lean docker image with minimum packages but enough to run node applications.

FROM node:10 AS BUILD_IMAGE

RUN curl -sfL https://install.goreleaser.com/github.com/tj/node-prune.sh | bash -s -- -b /usr/local/bin

WORKDIR /app

COPY . /app

EXPOSE 8080

RUN npm install && npm run build

# remove development dependencies
RUN npm prune --production

# run node prune
RUN /usr/local/bin/node-prune

FROM node:10-alpine

WORKDIR /app

# copy from build image
COPY --from=BUILD_IMAGE /app/dist ./dist
COPY --from=BUILD_IMAGE /app/node_modules ./node_modules

RUN npm i -g http-server

CMD http-server ./dist

By using this Dockerfile the image size dropped to 157MB \o/

docker4

Conclusion

By applying these 3 simple steps, we reduced our docker image size by 10 times.

Cheers!


Shivam Singhal

Shivam Singhal is a full stack developer, Linux Guy, Mozillian by ❤️.
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