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Connecting spring boot docker container to MQTT docker container

I'm trying to connect my containerized spring boot application with another containerized MQTT broker. Both of them are on their own projects as follows:
mqtt docker-compose.yml:
version: '3.9'
services:
mqttbroker:
container_name: mqttbroker
restart: always
volumes:
- ./config:/mosquitto/config
- ./data:/mosquitto/data
- ./log:/mosquitto/log
ports:
- 8883:8883
networks:
- mynetwork
volumes:
config:
data:
log:
mqtt Dockerfile
FROM eclipse-mosquitto
WORKDIR /mosquitto
COPY . .
EXPOSE 8883
And then the spring boot project is like:
spring boot docker-compose.yml
version: '3.8'
services:
myapp:
build: .
container_name: myapp
ports:
- '8082:8082'
stdin_open: true
tty: true
networks:
- mynetwork
In my application.properties I try to connect to the MQTT broker like:
mosquitto.url=tcp://mqttbroker:8883 and I get connection refused. However, if I run the spring boot application locally, I can connect to the docker container with mosquitto.url=tcp://localhost:8883.
I would rather have all the configurations in my docker-compose files to decrease manual codes.
I really appreciate your help in advance!

Yes, You do have to share the network as external.
you cab check the networks you have with this command : docker network ls
You would notice that they each have their own networks.
adding this to spring boot docker-compose file should fix the issue :
networks:
default:
name: mynetwork
external: true
For more information about docker compose networks

Connection to localhost:5432 refused. Check that the hostname and port are correct and that the postmaster is accepting TCP/IP connections. 2

I already tried everything i found, i know there are a few more questions about this but nothing worked.
I tried to change listen addresses from postgresql.conf, i tried changing methods to TRUST in pg_hba.conf, i tried to restart Postgresql servers...
When i execute docker compose-up my spring boot app works but is doesnt connect to the database, always saying that the port 5432 is already used.If i stop postgresql running on 5432 and i try to run again docker compose-up it says that 5432 is not found and it cannot connect, so basically i need to start it.
application.properties
spring.datasource.driver-class-name=org.postgresql.Driver
spring.datasource.username= postgres
spring.datasource.password=abc
spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect
spring.jpa.hibernate.ddl-auto=update
dockerfile-compose.yml
version: "3"
services:
postgres:
image: postgres:latest
network_mode: bridge
container_name: postgres
volumes:
- postgres-data:/var/lib/postgresql/data
expose:
- 5432
ports:
- 5432:5432
environment:
- POSTGRES_PASSWORD=abc
- POSTGRES_USER=postgres
- POSTGRES_DB=books
restart: unless-stopped
# APP*****************************************
springbootapp:
image: spring-app:latest
network_mode: bridge
container_name: spring-app
expose:
- 8080
ports:
- 8081:8080
restart: unless-stopped
depends_on:
- postgres
links:
- postgres
volumes:
postgres-data:
Dockerfile
FROM openjdk:12-jdk-alpine
VOLUME /tmp
EXPOSE 8081
RUN mkdir -p /app/
RUN mkdir -p /app/logs/
ADD target/spring-app-0.0.1-SNAPSHOT.jar /app/app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-Dspring.profiles.active=container", "-jar", "/app/app.jar"]

Docker: Springboot container cannot connect to PostgreSql Container

I am building a Spring Boot application which uses PostgreSQL with docker-compose.
When I run my containers using docker-compose up --build, my Spring Boot application fails to start because it does not find the PostgreSQL container's hostname.
Spring Boot Dockerfile
FROM maven:3.6.3-openjdk-14-slim AS build
COPY src /usr/src/app/src
COPY pom.xml /usr/src/app
RUN mvn -f /usr/src/app/pom.xml clean package
FROM openjdk:14-slim
COPY --from=build /usr/src/app/target/server-0.0.1-SNAPSHOT.jar /usr/app/server-0.0.1-SNAPSHOT.jar
EXPOSE 9000
ENTRYPOINT ["java","-jar","/usr/app/server-0.0.1-SNAPSHOT.jar"]
docker-compose.yml
version: '3'
services:
db:
image: postgres
environment:
POSTGRES_USER: postgres
POSTGRES_PASSWORD: postgres
POSTGRES_DB: my_db
ports:
- "5432:5432"
volumes:
- db-data:/var/lib/postgresql/data
networks:
- db-network
restart: always
server:
build: './server'
depends_on:
- db
restart: always
ports:
- "9000:9000"
networks:
- db-network
volumes:
- ./server:/server
networks:
db-network:
volumes:
db-data:
application.properties
spring.datasource.url=jdbc:postgresql://db:5432/my_db
spring.datasource.username=postgres
spring.datasource.password=postgres
Error output
Caused by: java.net.UnknownHostException: db
My guess is that docker-compose's virtual network isn't created yet during the build stage of the Spring Boot Dockerfile.
Any idea on how to solve this issue ?

Lots of info here: https://docs.docker.com/compose/networking/
Within the web container, your connection string to db would look like
postgres://db:5432, and from the host machine, the connection string
would look like postgres://{DOCKER_IP}:8001.
What this is saying is db:5432 is fine to use within docker-compose.yaml and the IP address will be passed (not "db"), but using it externally within your application code isn't going to work. You could however pass from docker-compose.yaml db as an application input variable, which your application could fill in in the configuration file. This would enable you then to connect.
Externalising configuration like this is fairly common practice so should be a relatively easy fix.
eg:
Docker-compose.yaml
version: '3'
services:
db:
container_name: db
image: postgres
environment:
POSTGRES_USER: postgres
POSTGRES_PASSWORD: postgres
POSTGRES_DB: my_db
ports:
- "5432:5432"
volumes:
- db-data:/var/lib/postgresql/data
networks:
- db-network
restart: always
server:
build: './server'
depends_on:
- db
environment:
DB_HOST: db # untested, but there should be a way to pass this in
DB_PORT: 5432
DB_DATABASE: my_db
DB_USER: postgres
DB_PASSWORD: postgres
restart: always
ports:
- "9000:9000"
networks:
- db-network
volumes:
- ./server:/server
networks:
db-network:
volumes:
db-data:
Then have an application.properties file located under src/main/java/resources/application.properties
spring.datasource.url=jdbc:postgresql://${DB_HOST}:${DB_PORT}/${DB_DATABASE}
spring.datasource.username=${DB_USERNAME}
spring.datasource.password=${DB_PASSWORD}

This post completely solved my issue.
It turns out that maven was trying to establish the connection to the database while building the .jar file. All I had to do is modify my Dockerfile with this line RUN mvn -f /usr/src/app/pom.xml clean package -DskipTests.

Please do note while building the images the service will not have access to the database as it is not yet running . Only after the images are built and the containers are running do the services have access . So when you try to pass a host as db , it is not yet available in the build stage . It is available only once the db container starts running .

Getting "Exception opening socket" on Mongodb connection from Spring App (docker-compose)

Even though I'm giving in the application properties,
spring.data.mongodb.host=api-database4
as the hostname which is the container name and hostname of the MongoDB on the docker-compose file, Spring app still can't connect to the MongoDB instance. I can however connect from MongoDB Compass to localhost:27030 but not to mongodb://api-database4:27030/messagingServiceDb.
My docker-compose file;
version: '3'
services:
messaging-api6:
container_name: 'messaging-api6'
build: ./messaging-api
restart: always
ports:
- 8085:8080
depends_on:
- api-database4
networks:
- shared-net
api-database4:
image: mongo
container_name: api-database4
hostname: api-database4
restart: always
ports:
- 27030:27017
networks:
- shared-net
command: mongod --bind_ip_all
networks:
shared-net:
driver: bridge
and my Docker file for the Spring app is;
FROM openjdk:12-jdk-alpine
ARG JAR_FILE=target/*.jar
COPY ${JAR_FILE} app.jar
ENTRYPOINT ["java","-jar","/app.jar"]
and my application.properties are;
#Local MongoDB config
spring.data.mongodb.database=messagingServiceDb
spring.data.mongodb.port=27030
spring.data.mongodb.host=api-database4
Entire code can be seen here.
How can I make my spring app on a docker container create a connection to the MongoDB instance which is on another docker container?
I have tried the solutions on similar questions and replicated them, it still gives the same error.
Edit and Solution:
I solved the issue by commenting out configuration below,
#Local MongoDB config
#spring.data.mongodb.database=messagingServiceDb
spring.data.mongodb.host=api-database4
spring.data.mongodb.port=27030
The remaining question is, why? That was the correct port that I'm trying to connect. Could it be related to the configuration order?

ports directive in docker-compose publishes container ports to the host machine. The containers communicate with each other on exposed ports. You can test whether a container can reach another with netcat.
docker exec -it messaging-api6 bash
> apt-get install netcat
> nc -z -v api-database4 27030
> nc -z -v api-database4 27017

Unable to connect to mysql in docker container from another docker container

I have two docker containers: mysql and spring boot service.
Service container is not connecting to mysql container(failing on the deploy) with following exception:
CommunicationsException: Communications link failure
So far I have tried using docker --link, docker networks, running everything using/without docker compose.
I am able to connect to DB container outside of docker.
Connection string: jdbc:mysql://db:3306/somedb
docker-compose.yml
version: '3.7'
services:
app:
build: .
restart: unless-stopped
ports:
- "80:8060"
links:
- db
depends_on:
- db
db:
image: "mysql:latest"
command: --default-authentication-plugin=mysql_native_password
environment:
- MYSQL_DATABASE=somedb
- MYSQL_ROOT_PASSWORD=somepassword
ports:
- "3306:3306"
volumes:
- /Users/someuser/someproject/mysql/data:/var/lib/mysql

I had the same problem earlier and i tried with by changing the mysql image version. Here is my compose yaml file where i am able to connect it with.
version: "3.0"
services:
spring-boot-container:
build: .
ports:
- "8086:8086"
links:
- mysql-standalone
mysql-standalone:
image: mysql:5.6
ports:
- "3307:3306"
environment:
MYSQL_ROOT_PASSWORD: password
MYSQL_DATABASE: springsecurity
MYSQL_USER: sa
MYSQL_PASSWORD: password

So in my service dockerfile I say:
ADD target/app-1.0-SNAPSHOT.jar /app-service.jar
RUN sh -c 'touch /app-service.jar'
But I forgot to rebuild jar after making changes in service config files
TL;DR I'm retarded