@bytesnz

Jack Farley, Computer Engineer

I have lots of services running on many different servers. Some have very little free hard drive space, so am always looking for an easy way to free some more.

On a recent hunt for some more space, I found that my NodeJS project Docker containers still had 100MB of yarn and npm caches in them (bad Jack). I have mostly switched over to yarn, so decided to look into that first.

A Sapper web app was one of the images that had the issue. Below is a the original Dockerfile that created a 236MB image.

FROM node:lts-alpine
EXPOSE 3000

RUN mkdir /app
WORKDIR /app

VOLUME /app/media
VOLUME /app/static

COPY package.json ./
RUN yarn install --prod --pure-lockfile

COPY __sapper__/build __sapper__/build

USER node

CMD [ "node", "__sapper__/build" ]

yarn has no way to disable the creation of a cache when installing modules (and is not going to in the near future). You also can't remove files from a docker container when you are building it, so you need to find a way of not adding them to your image in the first place.

One way to do this is using an intermediate images during the docker build process. This can be done by setting up the build image, installing the required node modules, then set up the main image, copying the node_modules folder (where all the node modules are installed) from the intermediate image. Below is a Dockerfile that does this produces an image that is 131MB.

# Set up a build image
FROM node:lts-alpine as build

RUN mkdir /app
WORKDIR /app

# Install the node dependencies
COPY package.json ./
RUN yarn install --prod --pure-lockfile

# Create the main image
FROM node:lts-alpine
EXPOSE 3000

RUN mkdir /app
WORKDIR /app

VOLUME /app/media
VOLUME /app/static

COPY package.json ./
# Copy the node_modules from the build image
COPY --from=build /app/node_modules/ node_modules

COPY __sapper__/build __sapper__/build

USER node

CMD [ "node", "__sapper__/build" ]

Alexander Kachkaev mentioned another way of achieving the same by changing yarn to use the /dev/shm directory as the place to store its cache. As /dev/shm is a memory-based temporary filesystem, it won't be included in the final docker image. The only issue with this method is that the /dev/shm filesystem is limited to 64MB. This can be changed by setting the size using the --shm-size argument when running docker build.

$ docker build -f docker/Dockerfile --shm-size 512M .

Below is an example Dockerfile that uses /dev/shm/yarn-cache for the yarn cache folder, again resulting in a 131MB docker image.

FROM node:lts-alpine
EXPOSE 3000

RUN mkdir /app
WORKDIR /app

VOLUME /app/media
VOLUME /app/static

COPY package.json ./
RUN yarn install --cache-folder /dev/shm/yarn-cache --prod --pure-lockfile

COPY __sapper__/build __sapper__/build

USER node

CMD [ "node", "__sapper__/build" ]