Docker compose. Networks. Spring Boot and MySQL connection - mysql

Question

I try to connect spring boot web app to database container.
And I can ping db container from web. But web can't connect to db by exposed 3307 port. But I can connect to db by internal container port 3306. Project very simple. What is may wrong?
This is my docker-compose.yml:
version: '3'
services:
db:
build:
context: ./db
dockerfile: Dockerfile
image: db
ports:
- "3307:3306"
volumes:
- demo_volume:/var/lib/mysql
networks:
- my-backend
web:
build:
context: ./web
dockerfile: Dockerfile
image: web
depends_on:
- db
ports:
- "18080:8080"
networks:
- my-backend
environment:
- DATABASE_HOST=db
- DATABASE_USER=user
- DATABASE_PASSWORD=password
- DATABASE_NAME=demo
- DATABASE_PORT=3307
- SPRING_PROFILES_ACTIVE=container
- DEBUG=true
volumes:
demo_volume:
driver: local
networks:
my-backend:
driver: bridge
It's simple enough.
My application.yml for active profile - container
spring:
profiles:
container
datasource:
url: jdbc:mysql://${DATABASE_HOST}:${DATABASE_PORT}/${DATABASE_NAME}?characterEncoding=UTF-8
username: ${DATABASE_USER}
password: ${DATABASE_PASSWORD}
driver-class-name: com.mysql.jdbc.Driver
jpa:
database-platform: org.hibernate.dialect.MySQLDialect
Also very simple
db Dockerfile:
FROM mysql:5.7
ENV MYSQL_ROOT_PASSWORD=admin
ENV MYSQL_DATABASE=demo
ENV MYSQL_USER=user
ENV MYSQL_PASSWORD=password
ADD dump.sql /docker-entrypoint-initdb.d/
And web Dockerfile:
FROM java:8-jre
COPY ./web.jar /app/web.jar
CMD ["java", "-jar", "/app/web.jar"]
CMD ["java", "-Xmx200m", "-Djava.security.egd=file:/dev/./urandom", "-jar", "/app/web.jar"]

Answer 1

Regarding Docker documentation all containers in the same bridge network (user defined) communicates via their internal ports. It's explained with image isolated_bridge_network
If you desire your containers should be available from external network you should publish ports for this one. Publish - means you should map internal ports to external environment. See on image
published_ports_from_isolated_bridge_network

Answer 2

You should link the Container to make it work.
web:
build:
context: ./web
dockerfile: Dockerfile
image: web
depends_on:
- db
ports:
- "18080:8080"
networks:
- my-backend
environment:
- DATABASE_HOST=db
- DATABASE_USER=user
- DATABASE_PASSWORD=password
- DATABASE_NAME=demo
- DATABASE_PORT=3307
- SPRING_PROFILES_ACTIVE=container
- DEBUG=true
links:
- db
Now inside your web Container /etc/hosts should have an entry for db Container