Reduce filesize for Docker image

From about 1 gigabyte to 400 megabytes

Author: TheKnarf

Dockerfile

@@ -1,11 +1,28 @@
-FROM node:14
+# Stage 1 - Build
+FROM node:14 AS builder
 
 WORKDIR /app
-COPY . /app/
 
-RUN yarn
+COPY package.json yarn.lock /app/
+RUN yarn --frosen-lockfile
+
+COPY . /app/
 RUN NEXT_TELEMETRY_DISABLED=1 yarn next build
 
+
+# Stage 2 - Running the app
+FROM node:14-alpine
+
+WORKDIR /app
+ENV NODE_ENV production
+
+# You only need to copy next.config.js if you are NOT using the default configuration
+ COPY --from=builder /app/next.config.js ./
+#COPY --from=builder /app/public ./public
+COPY --from=builder /app/.next ./.next
+COPY --from=builder /app/node_modules ./node_modules
+COPY --from=builder /app/package.json ./package.json
+
 EXPOSE 80
 
-ENTRYPOINT ["yarn", "start", "-p", "80"]
+ENTRYPOINT ["yarn", "next", "start", "-p", "80"]