docker-compose warning on scale containers - docker

Question

I've this docker-compose file:
version: "3.8"
services:
web:
image: apachephp:v1
ports:
- "80-85:80"
volumes:
- volume:/var/www/html
network_mode: bridge
ddbb:
image: mariadb:v1
ports:
- "3306:3306"
volumes:
- volume2:/var/lib/mysql
network_mode: bridge
environment:
- MYSQL_ROOT_PASSWORD=*********
- MYSQL_DATABASE=*********
- MYSQL_USER=*********
- MYSQL_PASSWORD=*********
volumes:
volume:
name: volume-data
volume2:
name: volume2-data
When run this:
docker-compose up -d --scale web=2
Its works as well but receive this warning:
WARNING: The "web" service specifies a port on the host. If multiple containers for this service are created on a single host, the port will clash.
Can somebody help to avoid these warning?, thank you advance.
Best regards.

Answer 1

I suppose, you try to access the web service without knowing the port of the specific container and to distribute the requests to a container here. If i rigth, to do that, you need a load balancing mechanisms to the system configuration.In the following example, i'll use NGINX as the load balancer.
version: "3.8"
services:
web:
image: apachephp:v1
expose: # change 'ports' to 'expose'
- "7483" # <- this is web running port (Change to your web port)
....
ddbb:
....
## New Start ##
nginx:
image: nginx:latest
volumes:
- ./nginx.conf:/etc/nginx/nginx.conf:ro
depends_on:
- web # your web service name
ports:
- "80:80"
## New End ##
volumes:
...
So you don’t need to map the port 80-85:80 from the web services to a host machine port, if you want to scale the service. So i remove the port mapping configuration from your Docker Compose file and only expose the port as above:
In the nginx service and i add port mappings to the host container for that server. In example, i configured NGINX to listen on the port 4000, which is why we have to add port mappings for this port.
nginx.conf file contents:
user nginx;
events {
worker_connections 1000;
}
http {
server {
listen 4000;
location / {
proxy_pass http://pspdfkit:5000;
}
}
}
You will find here more details, to Use Docker Compose to Run Multiple Instances of a Service in Development.