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How to connect to MySQL container on Docker using Spring Boot project

I am trying to run a Spring Boot application where db has to be connected to a MySQL container on Docker. I used following code and commands.
Application properties:
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://mysqldb:3306/practice
spring.datasource.username=root
spring.datasource.password=CVnit1234!
spring.jpa.show-sql=true
spring.sql.init.platform=mysql
spring.sql.init.mode=always
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
spring.jpa.hibernate.ddl-auto=update
Commands used for creating container & running it on Docker:
Pulling mysql image from Docker Hub:
docker pull mysql
Creating a container:
docker run --name mysqldb --network spring-net -p 3307:3306 -e MYSQL_ROOT_PASSWORD=password MYSQL_DATABASE=practice -d mysql:latest
After this command, a container is created and even it is up and working fine. I was able to login to sql bash and execute some queries.
I tried with multiple jdbc urls:
jdbc:mysql://mysqldb:3306/practice
jdbc:mysql://mysqldb:3307/practice
jdbc:mysql://mysqldb/practice
jdbc:mysql://host.docker.internal:3306/practice
jdbc:mysql://host.docker.internal:3307/practice
None of this worked, but I was able to connect to localhost:3306 and localhost:3307.
Below is my spring boot code. When I am trying to connect through the Spring Boot application, I was getting the following error.
com.mysql.cj.jdbc.exceptions.CommunicationsException:Communication link failure
The problem over here is when I am trying to connect to localhost the application is up and working, but when trying to connect to mysql container, I was not able to connect.

Check your network to ensure that the application network is connected to the MySQL network

Connection refused when trying to access containerized PostgreSQL

My setup is a Podman pod with PostgreSQL and pgAdmin that I created with these commands:
podman pod create --name postgre-sql -p 9876:80
podman run --name postgresql --pod postgre-sql -d -e POSTGRES_USER=admin -e POSTGRES_PASSWORD=admin docker.io/library/postgres
podman run --name pgadmin --pod postgre-sql -d -e 'PGADMIN_DEFAULT_EMAIL=admin#mail.com' -e 'PGADMIN_DEFAULT_PASSWORD=admin' docker.io/dpage/pgadmin4
Pod ran with no errors, I can enter pgAdmin, connect to the PostgreSQL container and configure my databases without a problem but when I try to connnect with a database on Java I get the following error message:
Connection to localhost:5432 refused. Check that the hostname and port
are correct and that the postmaster is accepting TCP/IP connections.
I've tried with these URL and none works (driver is correctly installed):
jdbc:postgresql://localhost:5432/db
jdbc:postgresql://localhost:9876/db
I've tried the solutions on other posts like this and this and none works for me.

How to call one microservice from another microservice using docker images

I have two SpringBoot microservices M1(port 2002) and M2(port 2004)
M1 and M2 are communicating successfully if I run them using eclipse (run as Java Project or SpringBoot Project).
However, I want to communicate them using Docker container.
So I build images for both Microservices (M1 and M2) using the command:
docker build -f Dockerfile -t image_name .
And run the images using:
docker run -p 2004:2004 image_name
Note: I am exposing same port from docker as defined above
But the M1 and M2 are not able to communicate.
I am using RestTemplate
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<Boolean> isUp = restTemplate.getForEntity("http://localhost:2002/apis/test",Boolean.class);
I am getting below exception :
I/O error on GET request for \"http://localhost:2002/apis/test\": Connection refused (Connection refused); nested exception is java.net.ConnectException: Connection refused (Connection refused)
However, If I call the other microservice using my machine's IP, It's communicating successfully
ResponseEntity<Boolean> isUp = restTemplate.getForEntity("http://XX.XX.XX.XXX:2002/apis/test",Boolean.class);
Can someone please tell if I am doing it write(using IP address) or there is another good approach to call one microservice from another using Docker?

Trying to communicate with the other container won't work with localhost.
You should create a custom bridged network, which will allow you to refer to the containers by name. And there is no need to publish the ports if you are only talking internally.
# create network
docker network create -d bridge mynet
# container 1
docker container run --network mynet --name container1 -d image_name
# container 2
docker container run --network mynet --name container2 -d some_other_image_name
The IP in code snippet can then be replaced with the name of the other container
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<Boolean> isUp = restTemplate.getForEntity("http://container2:2002/apis/test",Boolean.class)

Alternately, you can also link the two containers together by --link. Assuming you want container1 as client to container2, you can use below:
sudo docker run --link container2 --name=container1 -d image_name

Testcontainers with a company proxy

Each start of different testcontainers will throw com.github.dockerjava.api.exception.InternalServerErrorException: {"message":"Get https://quay.io/v1/_ping: dial tcp x.x.x.x: getsockopt: connection refused"}
This is no surprise (docker is behind a company proxy). How can I configure testcontainers to use a specific HTTP proxy?
Another approach could be disabling the "ping" command and using our company docker repo.

You can by specifying env variables when you are building an image or running a container. For example, below I'm building an Elasticsearch container by passing proxy configuration:
GenericContainer container = new GenericContainer("docker.elastic.co/elasticsearch/elasticsearch:6.1.1")
.withExposedPorts(9200)
.withEnv("discovery.type", "single-node")
.withEnv("HTTP_PROXY", "http://127.0.0.1:3001")
.withEnv("HTTPS_PROXY", "http://127.0.0.1:3001")
.waitingFor(Wait.forHttp("/_cat/health?v&pretty")
.forStatusCode(200));
Otherwise, you can set your proxy settings globally in docker. For windows with a docker machine you have to connect to it and the HTTP proxy in boot2docker profile.
docker-machine ssh default
sudo -s
echo "export HTTP_PROXY=http://your.proxy" >> /var/lib/boot2docker/profile
echo "export HTTPS_PROXY=http://your.proxy" >> /var/lib/boot2docker/profile
On Linux, you can create a file ~/.docker/config.json like :
{
"proxies":
{
"default":
{
"httpProxy": "http://127.0.0.1:3001",
"noProxy": "*.test.example.com,.example2.com"
}
}
}

Docker: Linking Spring Boot container with Mongo DB container

How can I link my Spring Boot application container with MongoDB container?
Spring Boot app is using MongoDBRespository which by default connects to localhost:27017.

You should use container linking. From the docs:
When you set up a link, you create a conduit between a source container and a recipient container. The recipient can then access select data about the source
When two containers are linked, Docker will set some environment variables in the target container to enable programmatic discovery of information related to the source container.
Basically what this means is the following
your MongoDB-container should expose some ports (either via the EXPOSE entry in the Dockerfile or via the -p option to docker run).
your Spring Boot-container should be started with the --link option that points to the MongoDB-container.
The MongoDBRepository should be configured to use the address that is provided in the environment variables by the linking.
Check out this article on how to link containers for more info.

#Himanshu Yadav , you can try this resource. it did solve my problem. :-) It has got a full tutorial in that regard
https://www.jiwhiz.com/blogs/Spring_Boot_Docker_MySQL_Demo
Quote
docker run -p 8080:8080 --name demo-app --link demo-mysql:mysql -d jiwhiz/spring-boot-docker-mysql

I wonder if you got this to work by linking containers, it didn't work for me, tried using a linked container alias as a dbhost name in my Springboot app. I did not try it as MongoClientURI though.
I did opt a work around, with mongodb containers and spring apps containers, I had to set up mongo containers host and port to spring app containers while creating the apps containers as Containers ENV variables , as shown below
Mongo container
docker run -d -p 27027:27017 -p 28027:28017 --name mongodb --volumes-from dbdata iamiddy/mongodb
SpringBoot Apps containers
docker run -d -p 8000:8080 --name AppDockerContainer
-e db.host.name=EC2-HOSTING-MONGO-CONTAINER
-e db.host.port=DB-HOST-PORT AppDockerImage
application.properties
db.host.port=27017
db.host.name=localhost
MongoConfig
public class MongoRepositoryConfig extends AbstractMongoConfiguration {
#Value("${db.host.port}")
private int port;
#Value("${db.host.name}")
private String host;
#Value("${db.name}")
private String dbname;
#Override
public Mongo mongo() throws Exception {
ServerAddress serverAdress = new ServerAddress(host,port);
Mongo mongo = new MongoClient(serverAdress);
mongo.setWriteConcern(WriteConcern.ACKNOWLEDGED);
return mongo;
}
public #Bean MongoTemplate mongoTemplate() throws Exception {
return new MongoTemplate(mongo(), getDatabaseName());
}
#Override
protected String getDatabaseName() {
return dbname;
}
}

As docker links are now deprecated, one can use user defined networks to achieve communication between containers.
Referring to Docker Networking, docker has 3 different types of networks - Bridge, Host, Network. Using docker network ls you can list all networks currently defined. By default docker comes with 1 for each type pre-configured.
While running your container, one can specify(--network=abcd) network the process will join - by default its the docker0 of type bridge.
Now, for the problem statement in the question here, the simplest approach is to use --network=host while launching mongo & spring-boot-app container.
docker run -d -P --name=my-mongo --network=host mongo:latest
Then in your Spring boot app, you will have something like this:-
spring:
application:
name: my-app
data:
mongodb:
database: app
host: 192.168.99.100 // your machine private ip.
port: 27017
Run you spring boot app from image using :-
docker run -d -P --name=my-boot-app --network=host my-app-image
You can then use/reach mongo & app instances as if they were run without docker.
(While using docker-toolbox on Windows, you are actually running docker inside a VM that has different IP - I found it to be 192.168.99.100 . So remember to use this ip instead of your local ip)