Docker: Connection PHP/Apache --> MySQL slow

Question

I would like to ask for help on my Docker installation, because I can't fix it. I have read a lot about slow Docker containers but all things I tried don't help.

When I browser the phpmyadmin UI it feels quite fast and tables/edits load quickly. But when I load my CMS it is slow (takes about 3 to 5 seconds) to load. Even the AJAX requests inside the CMS are slow. The CMS is very fast on my production webserver, in fact it is still faster than my local Docker installation. I guess there is a problem when connection form the webserver to the MySQL server. Had read about DNS problems with this, but couldn't find a way to solve it.

What I tried:

• use 'link' to connect the containers
• use 'network_mode: host'
• use 'networks: - mylocalnetwork' and 'networks: mylocalnetwork: driver: bridge'
• put the MySQL data inside the container (not on the host OS)
• changed ports
• some other, can't remember

Docker Version 2.0.0.0-mac81 (29211) (Engine: 18.09.0)

Docker-compose.yml:

version: '3'
services:
  db:
    image: mysql:5.7
    volumes:
      - "./.data/db:/var/lib/mysql"
    environment:
      MYSQL_DATABASE: devtest
      MYSQL_USER: root
      MYSQL_PASSWORD: pass
      MYSQL_ROOT_PASSWORD: pass
    ports:
      - "9906:3306"
    network_mode: "host"
  web:
    build: .
    depends_on:
      - db
    volumes:
      - /path/to/www:/var/www/html
    ports:
      - "8100:80"
      tty: true
    stdin_open: true
    network_mode: "host"
  phpmyadmin:
    image: phpmyadmin/phpmyadmin
    depends_on:
    - db
    external_links:
    - db:mysql
    ports:
    - "9191:80"
    environment:
        PMA_HOST: db
        MYSQL_USER: root
        MYSQL_ROOT_PASSWORD: pass
        MYSQL_PASSWORD: pass
    network_mode: "host"

Dockerfile

FROM php:7.2.2-apache

RUN docker-php-ext-install pdo_mysql
RUN docker-php-ext-install mysqli

#RUN apt-get update
#RUN apt-get install nano

RUN usermod -u 1000 www-data

RUN a2enmod rewrite
RUN a2enmod headers
RUN a2enmod expires

=== EDIT From Docker App Advanced Settings: CPU: 4 RAM: 2 GB SAWP 1 GB An exported SQL file is ~ 450 KB CMS says allocated memory peak is 19.56 MB