503 "Service Unavailable" of Docker container with Laravel 8 in Google Cloud

I am trying to run Laravel 8 (with the database!) in Google Cloud. Deployment is done via Cloud Run with GitHub CI Trigger

What I have done so far: I created all necessary Docker files for building the Docker image and container like the Dockerfile and docker-composer.yml in my apps doc root. Because my app needs a backend and a database, I created an nginx.conf-file and an int_db.sql file, to seed the database.

Dockerfile

FROM php:7.4-fpm

# Arguments defined in docker-compose.yml
ARG user=hannes
ARG uid=1002

# Install system dependencies
RUN apt-get update && apt-get install -y \
    git \
    curl \
    libpng-dev \
    libonig-dev \
    libxml2-dev \
    zip \
    unzip

# Clear cache
RUN apt-get clean && rm -rf /var/lib/apt/lists/*

# Install PHP extensions
RUN docker-php-ext-install pdo_mysql mbstring exif pcntl bcmath gd

# Get the latest Composer
COPY --from=composer:latest /usr/bin/composer /usr/bin/composer

# Create system user to run Composer and Artisan Commands
#RUN useradd -G www-data,root -u $uid -d /home/$user $user
RUN useradd -u 1002 -G www-data,root -d /home/$user $user
RUN mkdir -p /home/$user/.composer && \
    chown -R $user:$user /home/$user

# Set working directory
WORKDIR /var/www

USER $user

docker-compose.yml

version: "3.7"
services:
  app:
    build:
      args:
        user: hannes
        uid: 1002
      context: ./
      dockerfile: Dockerfile
    image: feedbackapp
    ports: 
      - 8080
    environment:
      # /run/docs/reference/container-contract
      PORT: ${PORT:-8080}
      K_SERVICE: feedbackapp
      K_REVISION: 0
      K_CONFIGURATION: feedbackapp
    container_name: feedbackapp-container
    restart: unless-stopped
    working_dir: /var/www/
    volumes:
      - ./:/var/www
    networks:
      - feedbackapp

  db:
    image: mysql:5.7
    container_name: feedbackapp-db
    restart: unless-stopped
    environment:
      MYSQL_DATABASE: homestead
      MYSQL_ROOT_PASSWORD: homestead
      MYSQL_PASSWORD: secret
      MYSQL_USER: homestead
      SERVICE_TAGS: dev
      SERVICE_NAME: mysql
    volumes:
      - ./docker-compose/mysql:/docker-entrypoint-initdb.d
    networks:
      - feedbackapp

  nginx:
    image: nginx:alpine
    container_name: feedbackapp-nginx
    restart: unless-stopped
    ports:
      - 8000:80
    volumes:
      - ./:/var/www
      - ./docker-compose/nginx:/etc/nginx/conf.d/
    networks:
      - feedbackapp

networks:
  feedbackapp:
    driver: bridge

feedbackapp.conf

server {
    listen 80;
    index index.php index.html;
    error_log  /var/log/nginx/error.log;
    access_log /var/log/nginx/access.log;
    root /var/www/public;
    location ~ \.php$ {
        try_files $uri =404;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass app:9000;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param PATH_INFO $fastcgi_path_info;
    }
    location / {
        try_files $uri $uri/ /index.php?$query_string;
        gzip_static on;
    }
}

In my local Docker environment, the Laravel 8 app gets successfully built and is working well, if i request the app via http://localhost:8000/. So I created a Cloud Run Service in Google Cloud with a CI trigger of my GitHub Repo. So every time I push my branch, my Cloud Run Service is triggered and builds my app. The build is finished successfully in Cloud Build.

Problem: if an open the apps link, I get a 503 Service Unavailable error Web

Network Status

What the log tells me: Log

Any help is much appreciated. Stay safe.