Nginx – Fixing Blank Page Issue in Docker Swarm for PHP/Laravel App

I have a Laravel application which I plan to deploy on a Docker Swarm.
The problem is that no matter what I do I get a blank page when calling localhost/index.php.

I'm using 2 separate services for:

1. Laravel App (php-fpm)
2. Nginx

Some notes which might be helpful to you helping me.

• The containers don't share anything but a volume for static files
• I can verify that requests are being received by php-fpm
• There is no error in any of the logs and all I get is 200 response codes both in my nginx logs and php-fpm
• Even a simple <?php phpinfo(); yields the same result so it's not a laravel problem

These are the Dockerfiles from which I build my images.

// Dockerfile for `Nginx`
FROM nginx

ADD ./api.conf /etc/nginx/conf.d/

RUN rm /etc/nginx/conf.d/default.conf

CMD ["nginx", "-g", "daemon off;"]

And this is the nginx config file:

server {
    listen 80;
    server_name _;
    root /app/public;

    add_header X-Frame-Options "SAMEORIGIN";
    add_header X-XSS-Protection "1; mode=block";
    add_header X-Content-Type-Options "nosniff";

    index index.html index.htm index.php;

    charset utf-8;

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }

    location = /favicon.ico { access_log off; log_not_found off; }
    location = /robots.txt  { access_log off; log_not_found off; }

    error_page 404 /index.php;

    location ~ \.php$ {
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass api:9000;
        fastcgi_index index.php;
        include fastcgi_params;
    }

    location ~ /\.(?!well-known).* {
        deny all;
    }
}

And this will be the Dockerfile for my laravel image:

FROM ubuntu:bionic

RUN apt update
RUN apt install -y software-properties-common
RUN add-apt-repository -y ppa:ondrej/php

RUN apt install -y php7.2-fpm
RUN apt install -y php7.2-pgsql
RUN apt install -y php7.2-mongodb
RUN apt install -y php7.2-redis
RUN apt install -y php7.2-mbstring
RUN apt install -y php7.2-xml
RUN apt install -y php7.2-zip
RUN apt install -y php7.2-curl
RUN apt install -y ffmpeg

RUN mkdir /run/php

COPY . /app

RUN chmod 0777 /app/storage -R

RUN sed  -i 's/pm.max_children = 5/pm.max_children = 10/g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's/pm.start_servers = 2/pm.start_servers = 4/g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's/pm.min_spare_servers = 1/pm.min_spare_servers = 3/g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's/pm.max_spare_servers = 3/pm.max_spare_servers = 5/g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's/;pm.max_requests = 500/pm.max_requests = 500/g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's|;access.log = log/$pool.access.log|access.log = /proc/self/fd/2|g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's|;php_admin_value[error_log] = /var/log/fpm-php.www.log|php_admin_value[error_log] = /proc/self/fd/2|g' /etc/php/7.2/fpm/pool.d/www.conf && \
    sed  -i 's|error_log = /var/log/php7.2-fpm.log|error_log = /proc/self/fd/2|g' /etc/php/7.2/fpm/php-fpm.conf && \
    sed  -i 's|listen = /run/php/php7.2-fpm.sock|listen = "9000"|g' /etc/php/7.2/fpm/pool.d/www.conf

WORKDIR /app

EXPOSE 9000

CMD ["php-fpm7.2", "-F"]

And the last think is my docker-compose.yml file:

version: "3"
services:
  nginx:
    image: hamed/nginx
    ports: 
      - 80:80
    volumes:
      - my-files:/app/public/files
  api:
    image: hamed/api
    volumes:
      - my-files:/app/public/files

Update:
The result of lsof -Pn | grep LISTEN | grep ':80 ' as requested by
@GerardH.Pille:

nginx      13     root    6u     IPv4             206078      0t0    TCP *:80 (LISTEN)

Update 2:
These are the logs from my nginx service:

10.255.0.2 - - [21/Aug/2018:12:27:32 +0000] "GET /index.php HTTP/1.1" 200 5 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:61.0) Gecko/20100101 Firefox/61.0" "-"

And from my php-fpm service:

10.0.0.2 -  21/Aug/2018:12:27:32 +0000 "- " 200