Installing and upgrading help

Hello the moodle community,

For a university project I must deploy a static website and a moodle instance (i have acces to one server: Ubuntu 16.04, php7.0, mysql5.7).

For this purpose i have stored the static website on the VPS host and I use a docker container for the moodle instance.

To make those two thing public, I use a nginx proxy with the following config in the server block:

server {  
  
    listen 80;  
  
    listen [::]:80;  
  
    server_name 104.238.164.33;  
  
    set $base /var/www/public/;  
  
    root $base;  
  
# $uri, index.html  
  
  location / {  
  
    try_files $uri $uri/ /index.html;  
  
  }  
  
  location /moodle/ {  
  
    proxy_pass http://172.20.0.3/;  
  
    proxy_redirect off;  
  
    proxy_set_header Host $host;  
  
    proxy_set_header X-Real-IP $remote_addr;  
  
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;  
  
    proxy_set_header X-Forwarded-Host $server_name;  
  
  }  
  
}  

the / location only hold static html.

the /moodle/ location point to the ip of the container, I build using this config:

https://github.com/jda/docker-moodle

To make it work i made the following change:

to make the moodle instace work behind the proxy, i just add in the config.php file line :

$CFG->reverseproxy=1;

Then I modify the docker-compose.yml to remove the exposed port

version: '3'  
  
services:  
dbapp:  
    image: mysql:5
    restart: always  
    volumes:  
        - db-volume:/var/lib/mysql  
    env_file:  
        - moodle_variables.env  
    networks:  
        - backendDB  

moodleapp:  
    build:  
        context: .  
    links:  
        - dbapp:DB  
    depends_on:  
        - dbapp  
    restart: always  
    volumes:  
        - moodleapp-data:/var/moodledata  
    env_file:  
        - moodle_variables.env  
    networks:  
       - backendDB  
       - frontendWEB  

  
volumes:  
    db-volume:  
    moodleapp-data:  
  
networks:  
    backendDB:  
    frontendWEB:

Then to make it use the last moodle version i change the git command in the Dockerfile

git clone -b MOODLE_34_STABLE git://git.moodle.org/moodle.git --depth=1 && \

Once all this is done you can build the image and deploy with:

docker-compose build  
docker-compose up -d

Once deployed i access the server with the following URL: http://104.238.164.33/moodle/

I can validate the license and all the plugins are installed, but once the installation script begin i get the error as showned in the attached screenshot.

When i check on the sql container all the table are created. What could make the server believe it cant access it ?
I am using this technique (proxy+docker) as it was the easiest path for me.
Seems like its an issue on the php side how could i debug this ?

Thank you for reading all this!