Kubernetes -- unable to connect to mysql from spring application - mysql

Question

I have kubernetes cluster. I have started mysql from kubectl. I have a image of spring boot application. I am confused with the JDBC url to be used in application.yml. I have tried multiple IP addresses by describing pods, services etc. It is getting errored out with "communication Link failure"
Below is my mysql-deployment.yml
apiVersion: v1
kind: Service
metadata:
name: mysql
spec:
#type: NodePort
ports:
- port: 3306
#targetPort: 3306
#nodePort: 31000
selector:
app: mysql
clusterIP: None
---
apiVersion: v1
kind: Secret
metadata:
name: mysql-secret
type: Opaque
data:
MYSQL_ROOT_PASSWORD: cGFzc3dvcmQ= #password
MYSQL_DATABASE: dGVzdA== #test
MYSQL_USER: dGVzdHVzZXI= #testuser
MYSQL_PASSWORD: dGVzdDEyMw== #test123
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: mysql-pv-claim
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 5Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: mysql
spec:
selector:
matchLabels:
app: mysql
strategy:
type: Recreate
template:
metadata:
labels:
app: mysql
spec:
containers:
- image: mysql:5.7
name: mysql
env:
# Use secret in real usage
- name: MYSQL_ROOT_PASSWORD
valueFrom:
secretKeyRef:
name: mysql-secret
key: MYSQL_ROOT_PASSWORD
- name: MYSQL_DATABASE
valueFrom:
secretKeyRef:
name: mysql-secret
key: MYSQL_DATABASE
- name: MYSQL_USER
valueFrom:
secretKeyRef:
name: mysql-secret
key: MYSQL_USER
- name: MYSQL_PASSWORD
valueFrom:
secretKeyRef:
name: mysql-secret
key: MYSQL_PASSWORD
ports:
- containerPort: 3306
name: mysql
volumeMounts:
- name: mysql-persistent-storage
mountPath: /var/lib/mysql
volumes:
- name: mysql-persistent-storage
persistentVolumeClaim:
claimName: mysql-pv-claim

Answer 1

Your K8S service should expose port and targetPort 3306 and in your JDBC URL use the name of that service:
jdbc:mysql://mysql/database
If your MySQL is a backend service only for apps running in K8S you don't need nodePort in the service manifest.
If you get a SQLException: Connection refused or Connection timed out or a MySQL specific CommunicationsException: Communications link failure, then it means that the DB isn't reachable at all.
This can have one or more of the following causes:
IP address or hostname in JDBC URL is wrong.
Hostname in JDBC URL is not recognized by local DNS server.
Port number is missing or wrong in JDBC URL.
DB server is down.
DB server doesn't accept TCP/IP connections.
DB server has run out of connections.
Something in between Java and DB is blocking connections, e.g. a firewall or proxy. 
I suggest these steps to better understand the problem:
Connect to MySQL pod and verify the content of the
/etc/mysql/my.cnf file
Connect to MySQL from inside the pod to verify it works
Remove clusterIP: None from Service manifest

Answer 2

Get the IP address of the node where the MySQL pod is running by running the command:-
kubectl get nodes -o wide
If the MySQL service is exposed to type NodePort get the assigned nodeport:-
kubectl get svc
In your application.properties edit the JDBC URL with
ip-address of node:nodeport assigned to that service

Answer 3

below is my output of kubectl get svc
kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 9d
mysql ClusterIP None <none> 3306/TCP 2h
registry NodePort 10.110.33.13 <none> 8761:31881/TCP 7d