Permission Denied for cp command on Bitnami Nginx Docker Image - bash

Question

I want to serve a static website using Bitnami's Nginx base image. I have a multi-stage Dockerfile as follows:
# build stage
FROM node:lts-alpine as build-stage
COPY ./ /app
WORKDIR /app
COPY .npmrc .npmrc
RUN npm install && npm run build
# Production stage
FROM bitnami/nginx:1.16 as production-stage
COPY --from=build-stage --chown=1001 /app/dist /app
COPY nginx.conf /opt/bitnami/nginx/conf/nginx.conf
COPY --chown=1001 entrypoint.sh /
RUN chmod +w /entrypoint.sh
CMD ["/entrypoint.sh"]
I use that entrypoint.sh to replace some file content with environment variables like:
#!/bin/bash
function join_by { local IFS="$1"; shift; echo "$*"; }
vars=$(env | grep VUE_APP_ | awk -F = '{print "$"$1}')
vars=$(join_by ' ' $vars)
for file in /app/js/app.*;
do
### T H I S L I N E T H R O W S E R R O R ###
cp $file $file.tmpl
envsubst "$vars" < $file.tmpl > $file
rm $file.tmpl
done
exec "$#"
On cp command it throws an error:
cp: cannot create regular file '/app/js/app.042ea3b0.js.tmpl': Permission denied
As you see, I have copied both the dist files and the entrypoint.sh with --chown=1001 (The default user in the Bitnami image), but no benefits.
Is it because the image folder app is exposed by a volume by default? How can I copy and modify that file I have moved into the image?
P.S: It runs in an OpenShift environment.

Answer 1

The Bitnami image performs some actions in the postunpack.sh script, this script is called from the Dokerfile. One of the actions perfomed by the script is related to configure the permissions due to the user running nginx is a non-root user. You can try implementing something similar with your needs.

Answer 2

It turned out to be a result of Openshift's behavior stated here:
How can I enable an image to run as a set user ID?:
When an application is deployed it will run as a user ID unique to the project it is running in. This overrides the user ID which the application image defines it wants to be run as.
...
The best solution is to build the application image so it can be run as an arbitrary user ID.
So, instead of copying the files and modifying the owner of them (chown), the access levels (chmod) of the files must be set appropriately.