Docker - Container IP addresses mapping - docker

Question

In Docker, I have 3 containers which are node, mysql and redis. When I run sudo iptables -t nat -L -n I can see those containers are running on different IP addresses like below
However, the IP addresses order for the services and the IP addresses (on some machine it's 172.23.0.x, on some machine it's 172.21.0.x) might be different every time I do docker-compose up --build so if I want the app works, I gotta config IP addresses for each service manually. Is there any way I can automatically map a fixed IP address for each service in the docker-compose.yml file? Thanks. Here's my docker-compose.yml file:
version: "3"
services:
universe:
build: .
working_dir: /usr/src
volumes:
- .:/usr/src
- /usr/src/node_modules/
ports:
- "3000:3000"
- "8000:8000"
restart: always
# Redis Alpine
redis:
image: redis:alpine
ports:
- "127.0.0.1:6379:6379"
# MySQL 5.7
mysql:
build:
context: ./docker/mysql
environment:
MYSQL_ROOT_PASSWORD: root
MYSQL_DATABASE: database_name
MYSQL_USER: database_user
MYSQL_PASSWORD: database_password
volumes:
- /config/scripts:/docker-entrypoint-initdb.d
restart: always
ports:
- "127.0.0.1:3306:3306"

Answer 1

You can try this type of docker-compose.yml configuration with defining a network with bridge connection including subnet and gateway for that defined network.
version: "3"
services:
universe:
build: .
working_dir: /usr/src
volumes:
- .:/usr/src
- /usr/src/node_modules/
ports:
- "3000:3000"
- "8000:8000"
restart: always
networks:
vpcbr:
ipv4_address: 10.3.0.2
# Redis Alpine
redis:
image: redis:alpine
ports:
- "6379:6379"
networks:
vpcbr:
ipv4_address: 10.3.0.3
# MySQL 5.7
mysql:
build:
context: ./docker/mysql
environment:
MYSQL_ROOT_PASSWORD: root
MYSQL_DATABASE: database_name
MYSQL_USER: database_user
MYSQL_PASSWORD: database_password
volumes:
- /config/scripts:/docker-entrypoint-initdb.d
restart: always
ports:
- "3306:3306"
networks:
vpcbr:
ipv4_address: 10.3.0.4
networks:
vpcbr:
driver: bridge
ipam:
config:
- subnet: 10.3.0.0/16
gateway: 10.3.0.1

Answer 2

In your Docker Compose setup as you’ve shown it, to communicate between containers, you can use the names of the services (universe, redis, mysql) as ordinary host names and they’ll resolve to the internal IP address of the container, whatever it happens to be.
Note that if you’re using the ports: option to remap a published port, you still need to connect to the internal port (the one on the right side of the colon). For instance you’d connect to mysql:3306 even if you specified a different external port mapping or not port mapping at all.
This doesn’t work from outside of Docker space; there you connect to the host’s DNS name or IP address with the published ports:, and the fact of Docker is totally hidden from you.