How to set up kubernetes for Spring and MySql - mysql

Question

i follow this tutorial https://medium.com/better-programming/kubernetes-a-detailed-example-of-deployment-of-a-stateful-application-de3de33c8632
I create mysql pod and backend pod, but when application get error com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
pod mysql: running
pod backend: CrashLoopBackOff
Dockerfile
FROM openjdk:14-ea-8-jdk-alpine3.10
ADD target/credit-0.0.1-SNAPSHOT.jar .
EXPOSE 8200
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom", "-Dspring.profiles.active=container","-jar","/credit-0.0.1-SNAPSHOT.jar"]
credit-deployment.yml
# Define 'Service' to expose backend application deployment
apiVersion: v1
kind: Service
metadata:
name: to-do-app-backend
spec:
selector: # backend application pod lables should match these
app: to-do-app
tier: backend
ports:
- protocol: "TCP"
port: 80
targetPort: 8080
type: LoadBalancer # use NodePort, if you are not running Kubernetes on cloud
---
# Configure 'Deployment' of backend application
apiVersion: apps/v1
kind: Deployment
metadata:
name: to-do-app-backend
labels:
app: to-do-app
tier: backend
spec:
replicas: 2 # Number of replicas of back-end application to be deployed
selector:
matchLabels: # backend application pod labels should match these
app: to-do-app
tier: backend
template:
metadata:
labels: # Must macth 'Service' and 'Deployment' labels
app: to-do-app
tier: backend
spec:
containers:
- name: to-do-app-backend
image: gitim21/credit_repo:1.0 # docker image of backend application
env: # Setting Enviornmental Variables
- name: DB_HOST # Setting Database host address from configMap
valueFrom:
configMapKeyRef:
name: db-conf # name of configMap
key: host
- name: DB_NAME # Setting Database name from configMap
valueFrom:
configMapKeyRef:
name: db-conf
key: name
- name: DB_USERNAME # Setting Database username from Secret
valueFrom:
secretKeyRef:
name: db-credentials # Secret Name
key: username
- name: DB_PASSWORD # Setting Database password from Secret
valueFrom:
secretKeyRef:
name: db-credentials
key: password
ports:
- containerPort: 8080
application.yml
spring:
datasource:
type: com.zaxxer.hikari.HikariDataSource
hikari:
idle-timeout: 10000
platform: mysql
username: ${DB_USERNAME}
password: ${DB_PASSWORD}
url: jdbc:mysql://${DB_HOST}/${DB_NAME}
jpa:
hibernate:
naming:
physical-strategy: org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
I placed the application.yml file in the application folder "resources"
EDIT
Name: mysql-64c7df597c-s4gbt
Namespace: default
Priority: 0
PriorityClassName: <none>
Node: minikube/192.168.8.160
Start Time: Thu, 12 Sep 2019 17:50:18 +0200
Labels: app=mysql
pod-template-hash=64c7df597c
tier=database
Annotations: <none>
Status: Running
IP: 172.17.0.5
Controlled By: ReplicaSet/mysql-64c7df597c
Containers:
mysql:
Container ID: docker://514d3f5af76f5e7ac11f6bf6e36b44ee4012819dc1cef581829a6b5b2ce7c09e
Image: mysql:5.7
Image ID: docker-pullable://mysql#sha256:1a121f2e7590f949b9ede7809395f209dd9910e331e8372e6682ba4bebcc020b
Port: 3306/TCP
Host Port: 0/TCP
Args:
--ignore-db-dir=lost+found
State: Running
Started: Thu, 12 Sep 2019 17:50:19 +0200
Ready: True
Restart Count: 0
Environment:
MYSQL_ROOT_PASSWORD: <set to the key 'password' in secret 'db-root-credentials'> Optional: false
MYSQL_USER: <set to the key 'username' in secret 'db-credentials'> Optional: false
MYSQL_PASSWORD: <set to the key 'password' in secret 'db-credentials'> Optional: false
MYSQL_DATABASE: <set to the key 'name' of config map 'db-conf'> Optional: false
Mounts:
/var/lib/mysql from mysql-persistent-storage (rw)
/var/run/secrets/kubernetes.io/serviceaccount from default-token-rgsmp (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
mysql-persistent-storage:
Type: PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
ClaimName: mysql-pv-claim
ReadOnly: false
default-token-rgsmp:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-rgsmp
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 49m default-scheduler Successfully assigned default/mysql-64c7df597c-s4gbt to minikube
Normal Pulled 49m kubelet, minikube Container image "mysql:5.7" already present on machine
Normal Created 49m kubelet, minikube Created container mysql
Normal Started 49m kubelet, minikube Started container mysql
Name: to-do-app-backend-8669b5467-hrr9q
Namespace: default
Priority: 0
PriorityClassName: <none>
Node: minikube/192.168.8.160
Start Time: Thu, 12 Sep 2019 18:27:45 +0200
Labels: app=to-do-app
pod-template-hash=8669b5467
tier=backend
Annotations: <none>
Status: Running
IP: 172.17.0.7
Controlled By: ReplicaSet/to-do-app-backend-8669b5467
Containers:
to-do-app-backend:
Container ID: docker://1eb8453939710aed7a93cddbd5046f49be3382858aa17d5943195207eaeb3065
Image: gitim21/credit_repo:1.0
Image ID: docker-pullable://gitim21/credit_repo#sha256:1fb2991394fc59f37068164c72263749d64cb5c9fe741021f476a65589f40876
Port: 8080/TCP
Host Port: 0/TCP
State: Waiting
Reason: CrashLoopBackOff
Last State: Terminated
Reason: Error
Exit Code: 1
Started: Thu, 12 Sep 2019 18:51:25 +0200
Finished: Thu, 12 Sep 2019 18:51:36 +0200
Ready: False
Restart Count: 9
Environment:
DB_HOST: <set to the key 'host' of config map 'db-conf'> Optional: false
DB_NAME: <set to the key 'name' of config map 'db-conf'> Optional: false
DB_USERNAME: <set to the key 'username' in secret 'db-credentials'> Optional: false
DB_PASSWORD: <set to the key 'password' in secret 'db-credentials'> Optional: false
DB_PORT: <set to the key 'port' in secret 'db-credentials'> Optional: false
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-rgsmp (ro)
Conditions:
Type Status
Initialized True
Ready False
ContainersReady False
PodScheduled True
Volumes:
default-token-rgsmp:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-rgsmp
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute for 300s
node.kubernetes.io/unreachable:NoExecute for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 25m default-scheduler Successfully assigned default/to-do-app-backend-8669b5467-hrr9q to minikube
Normal Pulled 23m (x5 over 25m) kubelet, minikube Container image "gitim21/credit_repo:1.0" already present on machine
Normal Created 23m (x5 over 25m) kubelet, minikube Created container to-do-app-backend
Normal Started 23m (x5 over 25m) kubelet, minikube Started container to-do-app-backend
Warning BackOff 50s (x104 over 25m) kubelet, minikube Back-off restarting failed container

Answer 1

First and foremost make sure that you fillfull all requirements that are described in article.
During creating deployments objects like (eg. pods, services ) environment variables are injected from the configMaps and secrets that are created earlier. This deployment uses the image kubernetesdemo/to-do-app-backend which is created in step one. Make sure you've created configmap and secrets before, otherwise delete created during deployment objects, create configMap, secret and then run deployment config file once again.
Another possibility if get:
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications
link failure
error 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.
~~4. 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 assume that if your mysql pod is running your DB server is running and point ~~4. DB server is down.~~ is wrong.
To solve the one or the other, follow the following advices:
Verify and test them with ping. Refresh DNS or use IP address in JDBC URL instead.
Check if it is based on my.cnf of MySQL DB.
Start the DB once again. Check if mysqld is started without the --skip-networking option.
Restart the DB and fix your code accordingly that it closes connections in finally.
Disable firewall and/or configure firewall/proxy to allow/forward the port.
Similar error you can find here: communication-error.