How to create a multi stage Dockerfile
Sometimes the scenario may arise like we have to do build the code as part of dockerfile itself in this case the final docker image will be very huge since the source code and dependecies are included in the final docker image.
Using the multi stage Dockerfile we can define two stages, one for building code and one for creatig final docker image. Once the code is built in firts stage now we can copy only the compiled code and add it in our second stage. This will make our final docker image light weight. Note the docker image is created only for the last stage, previous stages in dockerfile are not taken.
2 stage Dockerfile
To test this feature, I have a sample application code which is developed using Angular JS, we have to clone the repo first.
git clone https://github.com/vigneshsweekaran/easyclaim-frontend.git
FROM node:10.0 AS builder
COPY easyclaim-frontend .
RUN npm install \
&& npm run build
COPY --from=builder /build/dist/my-dream-app /usr/share/nginx/html
In the first stage we have used node:10.0 as base image for compiling the Angular Js source code, then copied the entire source code inside and then executing the npm install to download the dependencies and then running the npm run build to compile the source code. It will keep the compiled code in dist/my-dream-app.
Now we are intrested to copy only the compiled code from dist/my-dream-app folder to the Docker image, other files are not required during runtime.
Now create a second stage with nginx:alpine as base image and then copy the compiled code from first stage which are needed during runtime and put it to second stage
The final docker image is created from the second stage and first stage is thrown away.
Build a docker image
docker build -t 2-stage:latest .