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I have a Java Spring boot application deployed on a local Minikube cluster running on my machine.

The Java application connects to a mysql database and takes the configuration at runtime by using a DataSource Configuration. This is the DB config class:

public class DatasourceConfig 
 @Bean
 @Primary
 public DataSource dataSource() 
 DriverManagerDataSource dataSource = new DriverManagerDataSource();
 dataSource.setUrl(System.getProperty("mysql_user"));
 dataSource.setUsername(System.getProperty("mysql_user"));
 dataSource.setPassword(System.getProperty("mysql_pass"));

 return dataSource;
 

I pass the values for mysql_url, mysql_pass, mysql_userat runtime like this (from the Dockerfile):

ENTRYPOINT java -Dmysql_url=$mysql_url 
 -Dmysql_user=$mysql_user 
 -Dmysql_pass=$mysql_pass 
 -jar myapp.jar

I created another pod/deployment for local mysql container image and exposed it via a service locally.

this is the mysql.yml file for kubernetes:

apiVersion: v1
kind: Service
metadata:
 name: mysql-svc
 labels:
 app: mysql
spec:
 ports:
 - port: 3306
 nodePort: 30306
 targetPort: mysql-port
 protocol: TCP
 selector:
 app: mysql
 type: NodePort 
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
 name: mysql-pv-claim
 labels:
 app: mysql
spec:
 accessModes:
 - ReadWriteOnce
 resources:
 requests:
 storage: 5Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
 name: mysql-deployment
 labels:
 app: mysql
spec:
 replicas: 1
 selector:
 matchLabels:
 app: mysql
 tier: mysql
 strategy:
 type: Recreate
 template:
 metadata:
 labels:
 app: mysql
 tier: mysql
 spec:
 containers:
 - name: mysql
 image: mysql
 imagePullPolicy: Never
 ports:
 - name: mysql-port
 containerPort: 3306
 env:
 - name: MYSQL_ROOT_PASSWORD
 value: pass
 volumeMounts:
 - name: mysql-persistent-storage
 mountPath: /var/lib/mysql
 volumes:
 - name: mysql-persistent-storage
 persistentVolumeClaim:
 claimName: mysql-pv-claim

So, now I have two each of pods+deployment+services running on Minikube one for my application and other for mysql container: (below is the output of kubectl get all

NAME READY STATUS RESTARTS AGE
pod/mysql-deployment-8464d4875d-jlszz 1/1 Running 0 168m
pod/myapp-deployment-6469d8554b-4sbhz 1/1 Running 0 38m

NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 7d
service/mysql-svc NodePort 10.105.186.178 <none> 3306:30306/TCP 168m
service/myapp-svc NodePort 10.96.243.6 <none> 8080:31001/TCP 41m

NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/mysql-deployment 1/1 1 1 168m
deployment.apps/myapp-deployment 1/1 1 1 41m

NAME DESIRED CURRENT READY AGE
replicaset.apps/mysql-deployment-8464d4875d 1 1 1 168m
replicaset.apps/myapp-deployment-6469d8554b 1 1 1 41m

I can run the java application correctly from host machine, by doing this:

minikube service myapp-svc

and I can also connect to the Mysql from the host machine by doing this:

run minikube service mysql-svc --url which gives me: http://<mysql-ip>:30306

and then I can connect to it like this (from host machine):

mysql -h <mysql-ip> -P 30306 -u root -p .

This correctly connects me to the mysql running on the local kubernetes cluster through minikube.

I can even connect to the mysql service from inside the java container running on minikube:

first I connect into the java pod like this:

kubectl exec -it myapp-deployment-6469d8554b-4sbhz /bin/bash

and then I run mysql -h <mysql-ip> -P 30306 -u root -p inside the pod. Which also correctly connects me to the mysql running inside the other pod.

The only problem is this:

From inside the Java pod, when I check the application logs, I see this:

ERROR 1 --- [main] com.zaxxer.hikari.pool.HikariPool :
HikariPool-1 - Exception during pool initialization.

com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications
link failure

The last packet sent successfully to the server was 0 milliseconds
ago. The driver has not received any packets from the server.

and also, when ever I try to call any of the APIs which have database operations in them, I get the following error: Unable to acquire JDBC Connection; nested exception is org.hibernate.exception.JDBCConnectionException: Unable to acquire JDBC Connection

Which means that my Java code is actually unable to connect to the MySql deployed on the other pod.

I verified the the Java pod is successfully able to connect to the Mysql pod, then why is my Java code not able to connect??

I even verified this that I am able to run the docker java image locally by passing the mysql url of the pod deployed on minikube like this:

docker run -e mysql_url=jdbc:mysql://<mysql-ip>:<mysql-port>/my_db 
 -e mysql_user=root 
 -e mysql_pass=pass 
 --rm -p 8081:8080 --name myApp -it me/myapp

This verifies that my java code is correctly configured to connect to mysql (even the one deployed on the pod), when I run it locally.

So, it seems to me that mostly everything is configured correctly..

• The mysql pod itself is running correctly, which I verified by first connecting to it by using the mysql client locally.


• Java code is able to connect to the mysql running on Minikube when I run docker image locally.


• The Java pod on Minikube is able to connect to mysql pod which I verified by connecting to the mysql pod from within the java pod using the mysql client from bash.


• The java code is also running (sans the db connection part).

The only thing that is not working is that the Java app deployed inside Minikube is unable to connect to the mysql deployed in the other pod.

For that, the only point of failure that I can think of is the way Kubernetes passes on the ENV variables on to the docker image while running it.. But I even verified that by running env inside the bash running on my Java pod. which displayed that all the required environment variables are set there correctly.

This is my deployment file for java:

myapp.deployment.yml

apiVersion: apps/v1
kind: Deployment
metadata:
 name: myapp-deployment
 labels:
 app: myapp
spec:
 replicas: 1
 selector:
 matchLabels:
 app: myapp
 template:
 metadata:
 labels:
 app: myapp
 spec:
 containers:
 - name: myapp
 image: me/myapp
 imagePullPolicy: Never
 env:
 - name: mysql_url
 value: jdbc:mysql://<mysql-ip>:30306/my_db
 - name: mysql_user
 value: root
 - name: mysql_pass
 value: pass
 ports:
 - name: java-port
 containerPort: 8080

Should I also define a pod definition and provide the ENV variables there too ?

Is there something else that I need to do here as well ?

How can I fix this?

P.S.: I have already run eval $(minikube docker-env) in my current terminal window so that the local docker images are available to Minikube.