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Unable to connect tomcat container to mysql database container in kubernetes?

5/9/2019

Please don't mark this as duplicate.I have made some changes this time.Believe me, I have tried other answers and they don't seem to solve my issue.I am unable to link tomcat container with my MySQL database container in kubernetes.

Built my tomcat image using this dockerfile

FROM picoded/tomcat7
COPY data-core-0.0.1-SNAPSHOT.war /usr/local/tomcat/webapps/data-core-0.0.1-SNAPSHOT.war

mysql-service.yaml

apiVersion: v1
kind: Service
metadata:
  name: mysql
spec:
  ports:
  - port: 3306
  selector:
    app: mysql

mysql-deployment.yaml

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:5.6
        name: mysql
        imagePullPolicy: "IfNotPresent"
        env:
        - name: MYSQL_ROOT_PASSWORD
          value: root
        - name: MYSQL_DATABASE
          value: data-core  
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /docker-entrypoint-initdb.d   //my sql init script will 
                                                     get copied from hostpath 
                                                     of persistant volume. 
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-initdb-pv-claim

Tomcat-service.yaml

apiVersion: v1
kind: Service
metadata:
  name: tomcat
  labels:
    app: tomcat
spec:
  type: NodePort     
  ports:
  - name: myport
    port: 8080
    targetPort: 8080
    nodePort: 30000
  selector:
    app: tomcat
    tier: frontend

Tomcat-Deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: tomcat
  labels:
    app: tomcat
spec:
  selector:
    matchLabels:
      app: tomcat
      tier: frontend
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: tomcat
        tier: frontend
    spec:
      containers:
      - image: suji165475/vignesh:tomcatserver  //this is the tomcat image 
                                                  built using dockerfile with 
                                                  war file(spring boot app) 
                                                  copied to webapps folder
        name: tomcat
        env:
        - name: DB_PORT_3306_TCP_ADDR
          value: mysql                  #service name of mysql
        - name: DB_ENV_MYSQL_DATABASE
          value: data-core
        - name: DB_ENV_MYSQL_ROOT_PASSWORD
          value: root
        ports:
        - containerPort: 8080
          name: myport
        volumeMounts:
        - name: tomcat-persistent-storage
          mountPath: /var/data
      volumes:
      - name: tomcat-persistent-storage
        persistentVolumeClaim:
          claimName: tomcat-pv-claim

I have specified all the environment variables including the MySQL service name in the Tomcat deployment needed for connecting them.Also made sure to create persistent volumes and claims for both the containers.Yet my war file still wont start in tomcat's manager app.

Are my yaml files correct or is there still some changes to be made??

NOTE: I am running on a server using putty terminal.

URL used to access my app in browser-

206.189.22.155:30000/data-core-0.0.1-SNAPSHOT

-- Swetha Swaminathan

docker

kubernetes

mysql

tomcat

1 Answer

8/23/2019

Your YAML files are correct. I've recreated whole environment mentioned in the question and I've got healthy Tomcat with the application in the Running state.
If someone also wants to test it, Tomcat manager username/password are:

 username="the-manager" password="needs-a-new-password-here"

No SEVERE errors was found in the tomcat log, I've got the response from the application:

{"text":"Data-core"}

which looks like correct response. I've also got the empty table sequence in the Mysql database data-core.

I can guess yo've had some kind of connectivity problem, probably caused by incorrect work of Kubernetes network addon (Calico/Flannel/etc.)

How to troubleshot it:

To check the setup, all pods can be placed on the same node by creating PV for both deployment there.

To test connectivity to Mysql or Tomcat resources we can exec to their pods and run tests using simple commands:

$ kubectl exec mysql-pod-name -it -- mysql -hlocalhost -uroot -proot data-core --execute="show tables;"

or just run additional pod to check if services correctly points to the mysql pod:

$ kubectl run mysql-client --rm -it --image mysql --restart=Never --command -- mysql -hmysql -uroot -proot data-core --execute="show tables;"

For tomcat pod we can use the following commands to check the user passwords and application response:

   $ kubectl exec -ti tomcat-pod-name -- cat /usr/local/tomcat/conf/tomcat-users.xml

   $ kubectl exec -ti tomcat-pod-name -- curl http://localhost:8080/data-core-0.0.1-SNAPSHOT/

or use separate pod with curl or wget to check if Tomcat Service and NodePort works well:

   $ kubectl run curl -it --rm --image=appropriate/curl --restart=Never  -- curl http://tomcat:8080/data-core-0.0.1-SNAPSHOT/

   $ curl http://Cluster.Node.IP:30000/data-core-0.0.1-SNAPSHOT/

By using IPs of different nodes you can check also cluster connectivity because NodePort Service open the same port on all cluster nodes and then iptables rules on the nodes forward traffic to Pod's IP.
If pod is located on the different node, Flannel/Calico/etc. network plugin delivers it to the correct node and to the Pod.

-- VAS

Source: StackOverflow

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Unable to connect tomcat container to mysql database container in kubernetes?

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