Docker + Rails 6 + MySQL : Mysql2::Error::ConnectionError: Access denied for 'user'@'%' to database

Context : Rails 6 app hosted in Docker, using docker-compose

When the Rails container starts, I get :
Mysql2::Error::ConnectionError: Access denied for user 'user'@'%' to database 'db_production'
Even after MySQL is fully initalized

My docker-compose.yml :

services:

  app_production:
    image: app_production
    build:
      context: .
      dockerfile: ./dockerfiles/production.dockerfile
    container_name: app_production
    volumes:
      - ./public:/app_production/public
      - mysql_socket:/var/run/mysqld
    command: bash -c "sleep 5 && bundle exec rails db:create db:migrate && bundle exec puma -C config/puma.rb"
    restart: always
    environment:
      RAILS_ENV: production
      SECRET_KEY_BASE: ${PRODUCTION_SECRET_KEY_BASE}
      APP_DATABASE_PASSWORD: ${PRODUCTION_MYSQL_PASSWORD}
      PORT: 5000
    ports:
      - "5000:5000"
    depends_on:
      - database_production
    links:
      - database_production


  database_production:
    image: mysql:8.0.20
    command: mysqld --default-authentication-plugin=mysql_native_password
    restart: always
    container_name: database_production
    environment:
      MYSQL_USER: user
      MYSQL_PASSWORD: ${PRODUCTION_MYSQL_PASSWORD}
      MYSQL_RANDOM_ROOT_PASSWORD: "yes"
    volumes:
      - dbdata_production:/var/lib/mysql
      - mysql_socket:/var/run/mysqld
    ports:
      - "3307:3306"


volumes:
 dbdata_production:
 mysql_socket:

My Dockerfile :

FROM ruby:2.6.1

RUN echo "deb http://archive.debian.org/debian stretch main" > /etc/apt/sources.list
RUN curl https://deb.nodesource.com/setup_12.x | bash
RUN curl https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add -
RUN echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
RUN apt-get update && apt-get install -y nodejs yarn
RUN apt-get update && apt-get install -y gconf-service libasound2 libatk1.0-0 libc6 libcairo2 libcups2 libdbus-1-3 libexpat1 libfontconfig1 libgcc1 libgconf-2-4 libgdk-pixbuf2.0-0 libglib2.0-0 libgtk-3-0 libnspr4 libpango-1.0-0 libpangocairo-1.0-0 libstdc++6 libx11-6 libx11-xcb1 libxcb1 libxcomposite1 libxcursor1 libxdamage1 libxext6 libxfixes3 libxi6 libxrandr2 libxrender1 libxss1 libxtst6 ca-certificates fonts-liberation libappindicator1 libnss3 lsb-release xdg-utils wget
RUN apt-get install -y default-mysql-client

WORKDIR /app_production

RUN export RAILS_ENV=production
RUN gem install bundler:2.2.31

COPY Gemfile Gemfile.lock ./
COPY package.json ./
COPY vendor/gems/ vendor/gems/

RUN bundle install

COPY . ./

RUN yarn install --check-files

EXPOSE 5000

CMD ["RAILS_ENV=production", "bundle", "exec", "puma", "-C", "config/puma.rb"]

database.yml

default: &default
  adapter: mysql2
  encoding: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password:

production:
  <<: *default
  host: database_production
  port: 3306
  database: db_production
  username: user
  password: "some_password"
  socket: "/var/run/mysqld/mysqld.sock"

Notes :

• This configuration is working fine on another server on Ubuntu 22.04
• I’m now trying to make it works on this server on Ubuntu 20.04
• I had to add RUN apt-get install -y default-mysql-client to the Dockerfile in order to have MySQL working in the Rails container, otherwise it was not found, but on my other server I did not have to do this
• I also had to create a shared volume for mysql_socket:/var/run/mysqld otherwise socket was not found
• I am able to log to MySQL with CLI on the Rails container, using the same credentials
• If I put a phpMyAdmin service in docker-compose, I am also able to login to MySQL using the same credentials
• If I try to connect to MySQL via container’s rails console, it works
• If I remove bundle exec rails db:create db:migrate from rails container command, rails is launched

So I don’t understand much what exactly is happening, since I can successfully connect to MySQL through container’s CLI and PhpMyAdmin.
How come Rails can’t connect to it ? There are no detailed logs.

It fails at the step rake db:create and when trying to run it manually via rails console I got the same error. Very stange.

Any clue ?