How do I build docker images when my development e

Question

I dockerized my app, but in order to see my changes, I would have to rebuild my image and it wouldn't give me a live preview of my app.

So I created a docker-compose environment which links redis to my a node container, and then mounts the source code from the host to the node app and watches it for changes. However, since the code isn't part of UnionFS, it can't be containerized.

How do I setup a development environment which can produce dockerized images but doesn't have to be restarted every time I make a change to the codebase?

Answer 1

The container image you develop with and mount directories in should be the same image you produce to run the app elsewhere, or at least based the production image if that can't be achieved.

Using a simple node app as an example, here is the base image:

FROM node:6
ENV NODE_ENV=production
RUN npm install forever -g
COPY docker-entrypoint.sh /entrypoint.sh
WORKDIR /app
COPY package.json /app/
RUN npm install
COPY . /app
EXPOSE 3000
ENTRYPOINT ["/entrypoint.sh"]
CMD ["node", "/app/index.js"]

Production

docker run \
  --detach \
  --restart always \
  --publish 3000:3000 \
  myapp

Development

docker run \
  --publish 3000:3000 \
  --volume .:/app \
  --env NODE_ENV=development \
  myapp \
  forever -w /app/index.js

So I've modified the mount, but the base image is the same. The mounted files replace the "built" files in the container.

In the case of a node.js application, there's a couple of extra development changes. An environment variable and the command used to watch/restart the process on changes. You also need to manually exec an npm install in the container with docker exec $container npm install when you make changes to the dependencies in package.json.

Development Dockerfile

If you require a number of modifications for a development environment and don't want to specify them manually you can create a development image FROM your base image that houses the development specifics. Dockerfile.dev:

from myapp:latest
env NODE_ENV=development
volume ["/app"]
command ["forever", "-w", "--watchDirectory", "/app" "/app/index.js"]

Then the dev specifics are stored in the new image but still linked to your real image.

docker build -f Dockerfile.dev -t myapp-dev .
docker run -p 3000:3000 -v .:/app myapp-dev