Docker creating multiple images

Question

I am new to Docker and find that there are numerous images that are getting created (as seen in sudo docker images) and found somewhere in stackoverflow to periodically run sudo docker rmi $(sudo docker images -q) to remove all images. Why so many images get created? is there something wrong in my configuration?

docker-compose.yml

nginx:
  build: ./nginx
  restart: always
  ports:
    - "80:80"
    - "443:443"
  volumes:
    - /etc/letsencrypt/:/etc/letsencrypt/
  links:
    - node:node

node:
  build: ./node
  restart: always
  ports:
   - "8080:8080"
  volumes:
    - ./node:/usr/src/app
    - /usr/src/app/node_modules

The nginx dockerfile is

FROM nginx:alpine

COPY nginx.conf /etc/nginx/conf.d/default.conf

The nodejs dockerfile is

FROM node:9.3.0-alpine

WORKDIR /usr/src/app

COPY package*.json /usr/src/app/

RUN npm install --only=production

COPY . /usr/src/app

EXPOSE 8080
CMD [ "npm", "start" ]

The website/app works fine. Except that periodically, I am removing all containers, images and then run: sudo docker-compose up --build -d.

Answer 1

Images are immutable, so any change you make results in a new image being created. Since your compose file specifies the build command, it will rerun the build command when you start the containers. If any files you are including with a COPY or ADD change, then the existing image cache is no longer used and it will build a new image without deleting the old image.

Note, I'd recommend naming your image in the compose file so it's clear which image is being rebuilt. And you can watch the compose build output to the the first step that doesn't report using the cache to see what is changing. If I was to guess, the line that breaks your cache and causes a new image is this one in nodejs:

COPY . /usr/src/app

If the files being changed and causing the rebuild are not needed in your container, then use a .dockerignore file to exclude the unnecessary files.

Answer 2

I had the same problem when I was building my Dockerfile.

I found the solution, use this command to build your file :

`docker build --rm -t <tag> .`

The option --rm removes intermediate containers after a successful build.