multiple docker compose container - single ip - networking

Question

I have this application.
How can I assign a single ip-address to the web-service and use the database within?
version: "2"
services:
web:
image: kartoffeltoby/typo3:latest
hostname: localhost
container_name: web
ports:
- 80:80
link:
- db:database
volumes:
- ./www/:/var/www/
environment:
- DOCROOT=/var/www/web
- PAGESPEED=Off
db:
image: mysql:5.6
hostname: database
volumes:
- ./DB/:/var/lib/mysql/
- ./db/:/var/tmp/db
environment:
- MYSQL_ROOT_PASSWORD=passwort

Answer 1

The solution is:
network_mode: service:web
version: "2"
services:
typo3:
image: kartoffeltoby/typo3:latest
hostname: axdbw.vagrant
container_name: typo3
volumes:
- ./www/:/var/www/
environment:
- DOCROOT=/var/www/web
- PAGESPEED=Off
networks:
mynet:
ipv4_address: 172.16.47.14
db:
image: mysql:5.6
volumes:
- ./DB/:/var/lib/mysql/
- ./db/:/var/tmp/db
environment:
- MYSQL_ROOT_PASSWORD=passwort
network_mode: service:web
networks:
mynet:
driver: bridge
ipam:
driver: default
config:
- subnet: 172.16.47.0/24

Answer 2

There is no reason to use a specific IP. The solution can be as simple as this:
version: "3"
services:
typo3:
image: kartoffeltoby/typo3:latest
container_name: typo3
networks:
- mynet
db:
image: mysql:5.6
network_mode: "service:typo3"
networks:
mynet:
driver: bridge
This will place the db container onto the same IP as the typo3 container. Beware of possible port collisions.
In my use-case, I had to avoid nasty cross origin errors. Hosting the database on the same IP as my frontend container helped get around those issues.