Use a multi-step build to obtain a smaller final image size

Dockerfile

# use a builder for all your dependencies including Typescript compilation
FROM node:18.17.1 as builder

WORKDIR /opt/app

# Install dependencies
COPY package*.json .
RUN npm install 

# receive secrets using the --build-arg command e.g. from github actions secrets
# and set them as environment variables since next needs them at build time
# repeat this as needed for your secrets -> environment variables
ARG some_secret
ENV SOME_SECRET $some_secret


# build the app 
COPY . . 
RUN npm run build


# set up a runner using a node alpine or node slim image for a smaller final image
FROM node:18.17.1-alpine as runner

WORKDIR /opt/app 

# in case you are using runtime environment variables 
ARG some_secret 
ENV SOME_SECRET $some_secret

# copy over next configurations, build and public folders
COPY --from=builder /opt/app/next.config.js ./ 
COPY --from=builder /opt/app/public ./public 
COPY --from=builder /opt/app/.next ./.next

# copy over your package.json file AND lock file if necessary 
COPY --from=builder /opt/app/package*.json ./

# only install production dependencies. Make sure you have properly separated your devDependencies in package.json
# this is one of the BEST things you can do to reduce your final image size aside from using alpine/slim
RUN npm install --production

EXPOSE 3000
CMD npm run start