Docker, Nginx and PHP7: ERROR 111 Connection refused while connecting to upstream - php

Question

I run a NGINX-PHP7-COMPOSER image that works well but when using Slim Framework I had to change Nginx's default config to make the URL rewrites work.
And now it show this error in the logs:
2017-01-21 14:38:34,357 INFO success: php-fpm7 entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2017-01-21 14:38:34,359 INFO success: nginx entered RUNNING state, process has stayed up for > than 1 seconds (startsecs)
2017/01/21 14:38:37 [error] 15#15: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 172.18.0.1, server: auth-api, request: "GET /hello HTTP/1.1", upstream: "fastcgi://172.18.0.6:9000", host: "localhost:9100"
172.18.0.1 - - [21/Jan/2017:14:38:37 +0000] "GET /hello HTTP/1.1" 502 537 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_2) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.95 Safari/537.36"
The config file I mounted is loaded (I checked the bash with nginx -T):
server {
listen 80;
server_name auth-api;
index index.php;
root /var/www/html;
location / {
try_files $uri /index.php$is_args$args;
}
location ~ \.php {
try_files $uri =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
fastcgi_index index.php;
fastcgi_pass auth-api:9000;
}
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root /usr/share/nginx/html;
}
}
My Dockerfile (just the image i am loading from the repository):
FROM richarvey/nginx-php-fpm
And my docker-compose.yml:
version: '2'
services:
#############
## MARIADB ##
#############
mariadb:
image: mariadb
restart: always
volumes:
- "./log/mariadb:/var/log/mysql:rw"
- "./data/mariadb:/var/lib/mysql:rw"
environment:
- "MYSQL_ROOT_PASSWORD=pass"
ports:
- "3306:3306"
##############
## FRONTEND ##
##############
frontend:
image: skiychan/nginx-php7:latest
volumes:
- ./services/frontend/src:/data/www
links:
- mariadb:mysql
ports:
- "9001:80"
##############
## AUTH API ##
##############
auth-api:
build: ./services/api/auth/
volumes:
- ./services/api/auth/code/:/var/www/html
- ./services/api/auth/:/etc/nginx/sites-available/
links:
- mariadb:mysql
ports:
- "9100:80"
- "9000:9000"
Do you have any idea of what is going wrong?