Permission denied when attempting to edit docker container files - docker-compose

Question

I'm working on a Dockerized project which has an Adminer container. I need to increase the value of post_max_size found in /usr/local/etc/php/conf.d/0-upload_large_dumps.ini.
My problem is any attempt to edit the file results in permission denied responses. Usually, this would be a prolem resolved by using sudo but I also get permission denied from that as well.
The following is the output of the directory I'm trying to edit showing the target file is owned by root:
/var/www/html $ cd /usr/local/etc/php/conf.d/
/usr/local/etc/php/conf.d $ ls -l
total 24
-rw-r--r-- 1 root root 113 Nov 18 22:10 0-upload_large_dumps.ini
-rw-r--r-- 1 root root 23 Nov 18 22:11 docker-php-ext-pdo_dblib.ini
-rw-r--r-- 1 root root 23 Nov 18 22:10 docker-php-ext-pdo_mysql.ini
-rw-r--r-- 1 root root 22 Nov 18 22:11 docker-php-ext-pdo_odbc.ini
-rw-r--r-- 1 root root 23 Nov 18 22:11 docker-php-ext-pdo_pgsql.ini
-rw-r--r-- 1 root root 17 Nov 18 17:03 docker-php-ext-sodium.ini
And the adminer section of docker-compose is as follows:
adminer:
image: adminer
restart: always
labels:
- traefik.port=8080
- traefik.frontend.rule=Host:adminer
How can I edit docker-compose so I have permissions to update the files?

Answer 1

There is nothing to change in your docker-compose.yaml.
If you want to change it, you can just exec in the container as the root user.
So I suppose that, right now, you are doing
docker compose exec adminer ash
And then, you are trying to edit those file.
What you can do, instead, is:
docker compose exec --user root adminer ash
So you will be able to adapt those files owned by root.
This said, mind that the philosophy of Docker is that a container should be short lived, so you would be better having your own Dockerfile to edit that configuration file for good. Another way to do it would be to mount a file over the existing one to change the configurations.
Example of adaptation in a Dockerfile:
FROM adminer
COPY ./0-upload_large_dumps.ini \
/usr/local/etc/php/conf.d/0-upload_large_dumps.ini
## ^-- copies a files from the folder where you build
## in order to override the existing configuration
Then in your docker-compose.yml:
adminer:
build: .
image: your-own-namespace/adminer
restart: always
labels:
- traefik.port=8080
- traefik.frontend.rule=Host:adminer
Example of mounting a file to override the configuration file:
adminer:
image: adminer
restart: always
labels:
- traefik.port=8080
- traefik.frontend.rule=Host:adminer
volumes:
- "./0-upload_large_dumps.ini:\
/usr/local/etc/php/conf.d/0-upload_large_dumps.ini"
## a local file `0-upload_large_dumps.ini` on your host
## will override the container ini file