Modifying Wordpress official docker image to work on subdirectory - wordpress

Question

I am planning to use Wordpress official docker image on Amazon ECS. The problem is that instead working on the root path https://www.example.com/, I need it to work on a subdirectory path https://www.example.com/blog/.
To modify this I am planning to create a new Docker image based on the official Wordpress docker image.
My current Dockerfile looks like this.
FROM wordpress:6.0.1-apache
# Copying to premium so user can access it through
# domain/blog
RUN cd /var/www/html; \
mkdir blog; \
cp !\(blog\) blog; \
# We copy the wordpress instance to subdirectory and disable
# access to the root instance.
echo "Hello World!" > /var/www/html/index.php;
However this doesn't work. When I access https://www.example.com/blog it shows Forbidden.
The log shows this
[autoindex:error] [pid 23] [client 172.30.0.1:61822] AH01276: Cannot serve directory /var/www/html/blog/: No matching DirectoryIndex (index.php,index.html) found, and server-generated directory index forbidden by Options directive
It seems that the image does not copy the wordpress library.
wordpress % docker compose exec wordpress bash
root#63d417de7f31:/var/www/html# ls
index.php blog wp-config.php wp-content
root#63d417de7f31:/var/www/html# ls -al
total 32
drwxrwxrwx 4 www-data www-data 4096 Aug 5 06:13 .
drwxr-xr-x 1 root root 4096 Aug 2 07:49 ..
-rw-r--r-- 1 root root 13 Aug 5 06:06 index.php
drwxr-xr-x 2 root root 4096 Aug 5 06:06 blog
-rw-r--r-- 1 www-data www-data 5584 Aug 5 06:13 wp-config.php
drwxrwxrwx 5 www-data www-data 4096 Aug 5 06:13 wp-content
root#63d417de7f31:/var/www/html# ls -al blog/
total 8
drwxr-xr-x 2 root root 4096 Aug 5 06:06 .
drwxrwxrwx 4 www-data www-data 4096 Aug 5 06:13 ..
root#63d417de7f31:/var/www/html# exit
What should I do?
Update 1
When I trim the Dockerfile to just the base image like this,
FROM wordpress:6.0.1-apache
the wordpress files are copied into /var/www/html.
% docker compose exec wordpress bash
root#f9ad22323268:/var/www/html# ls
index.php wp-admin wp-config-sample.php wp-includes wp-mail.php xmlrpc.php
license.txt wp-blog-header.php wp-config.php wp-links-opml.php wp-settings.php
readme.html wp-comments-post.php wp-content wp-load.php wp-signup.php
wp-activate.php wp-config-docker.php wp-cron.php wp-login.php wp-trackback.php
Update 2
I tried using this
FROM wordpress:6.0.1-apache
WORKDIR /var/www/html/blog
This copies the Wordpress installation both in /var/www/html and /var/www/html/blog. This still fits the requirement, however I want to remove the one in /var/www/html/. I tried rewriting to /var/www/html/index.php like below
FROM wordpress:6.0.1-apache
WORKDIR /var/www/html/blog
RUN echo "Hello World!" > /var/www/html/index.php
But it's not rewritten. Seems like it's being rewritten from the entrypoint
https://github.com/docker-library/wordpress/blob/master/docker-entrypoint.sh

Answer 1

Give Apache user access to blog directory. By adding following to Dockerfile
RUN chown -R www-data:www-data /var/www/html/blog