Made additional cleanups as per recs by SuperSandro

backend/Dockerfile

@@ -3,6 +3,7 @@ FROM alpine:3.12
 ENV UID=1000 \
   GID=1000 \
   USER=youtube
+
 RUN addgroup -S $USER -g $GID && adduser -D -S $USER -G $USER -u $UID
 
 RUN apk add --no-cache \
@@ -13,21 +14,14 @@ RUN apk add --no-cache \
   && apk add --no-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing/ \
     atomicparsley
 
-# switch to default user to not chown node_modules on startup
-USER $USER
 WORKDIR /app
 COPY --chown=$UID:$GID [ "package.json", "package-lock.json", "/app/" ]
 
-# run npm install as root, required for Windows hosts
-USER root
-RUN npm install
-
-RUN chown -R $UID:$GID ./
+RUN npm install && chown -R $UID:$GID ./
 
 COPY --chown=$UID:$GID [ "./", "/app/" ]
 
 EXPOSE 17442
-# switch back to root to allow UID/GID changing
-USER root
+
 ENTRYPOINT [ "/app/entrypoint.sh" ]
 CMD [ "node", "app.js" ]