Docker shared network with multiple nginx instances, gives random nginx instance - docker

Question

I am setting up the following docker containers with the following 2 docker-compose files:
version: '3.7'
services:
mysql:
image: mysql:5.7
restart: on-failure
environment:
MYSQL_DATABASE: ${MYSQL_DATABASE}
MYSQL_USER: ${MYSQL_USER}
MYSQL_PASSWORD: ${MYSQL_PASSWORD}
MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
volumes:
- db_data:/var/lib/mysql:rw
ports:
- '${MYSQL_PORT}:3306'
networks:
- shared_mysql
php:
build:
context: .
dockerfile: docker/php/Dockerfile
restart: on-failure
volumes:
- '../:/usr/src/app'
user: ${LOCAL_USER}
networks:
- shared_mysql
api_nginx:
image: nginx:1.15.3-alpine
restart: on-failure
volumes:
- '../public/:/usr/src/app'
- './docker/nginx/default.conf:/etc/nginx/conf.d/default.conf:ro'
ports:
- '21180:80'
depends_on:
- php
networks:
- shared_mysql
phpmyadmin:
image: phpmyadmin/phpmyadmin
restart: on-failure
ports:
- '${PHPMYADMIN_PORT}:80'
environment:
PMA_HOST: mysql
MYSQL_USERNAME: ${MYSQL_USER}
MYSQL_ROOT_PASSWORD: ${MYSQL_PASSWORD}
networks:
- shared_mysql
volumes:
db_data:
networks:
shared_mysql:
version: '3.7'
services:
php:
build:
context: .
dockerfile: docker/php/Dockerfile
restart: on-failure
volumes:
- '../:/usr/src/app'
user: ${LOCAL_USER}
networks:
- api_21s_shared_mysql
auth_nginx:
image: nginx:1.15.3-alpine
restart: on-failure
volumes:
- '../public/:/usr/src/app'
- './docker/nginx/default.conf:/etc/nginx/conf.d/default.conf:ro'
ports:
- '21181:80'
depends_on:
- php
networks:
- api_21s_shared_mysql
volumes:
db_data:
networks:
api_21s_shared_mysql:
external: true
When I visit http://localhost:21181/, I always get the correct website.
But when I visit http://localhost:21182/, I get http://localhost:21181/ or http://localhost:21182/ random.
I tried to set up the network sepperate.
I'd like it to work with the portnumbers, but I don't want them to be mixed up.
I am hoping someone can help me. Thank you in advance.

Answer 1

When services are started with docker-compose, they are discoverable within the docker network in different ways: by service name, by container name, by IP, etc.
In your case you use the discovery by service name, since in your nginx configuration you have the reference "php:9000".
At this point docker looks for a service named "php" and finds 2. It interprets them as replicas of the same service and sends traffic to them following a round-robin pattern (first request to first instance of the service, second to the second instance of the service, third to the first instance, forth to the second instance, etc.)
Solution
Name the services differently, just like you already do with your nginx services (auth_nginx and api_nginx).
Then in your default.conf for both services change the line referring to php:9000 accordingly.