Mysql Communications link failure in kubernetes sample - mysql

Question

Step1:finish installing etcd and kubernetes with YUM in CentOS7 and shutdown firewall
Step2:modify related configuration item in /etc/sysconfig/docker
OPTIONS='--selinux-enabled=false --insecure-registry gcr.io'
Step3:modify related configuration item in /etc/kubernetes/apiserver
remove
ServiceAccount
in KUBE_ADMISSION_CONTROL configuration item
Step4:start all the related services of etcd and kubernetes
Step5:start ReplicationController for mysql db
kubectl create -f mysql-rc.yaml
apiVersion: v1
kind: ReplicationController
metadata:
name: mysql
spec:
replicas: 1
selector:
app: mysql
template:
metadata:
labels:
app: mysql
spec:
containers:
- name: mysql
image: hub.c.163.com/library/mysql
ports:
- containerPort: 3306
env:
- name: MYSQL_ROOT_PASSWORD
value: "123456"
Step6:start related mysql db service
kubectl create -f mysql-svc.yaml
kind: Service
metadata:
name: mysql
spec:
ports:
- port: 3306
selector:
app: mysql
Step7:start ReplicationController for myweb
kubectl create -f myweb-rc.yaml
apiVersion: v1
kind: ReplicationController
metadata:
name: myweb
spec:
replicas: 3
selector:
app: myweb
template:
metadata:
labels:
app: myweb
spec:
containers:
- name: myweb
image: docker.io/kubeguide/tomcat-app:v1
ports:
- containerPort: 8080
env:
- name: MYSQL_SERVICE_HOST
value: "mysql"
- name: MYSQL_SERVICE_PORT
value: "3306"
Step8:start related tomcat service
kubectl create -f myweb-svc.yaml
apiVersion: v1
kind: Service
metadata:
name: myweb
spec:
type: NodePort
ports:
- port: 8080
nodePort: 30001
selector:
app: myweb
When I visit from browser with nodeport(30001),I get the following Exception:
Error:com.mysql.jdbc.exceptions.jdbc4.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.
kubectl get ep
NAME ENDPOINTS AGE
kubernetes 192.168.57.129:6443 1d
mysql 172.17.0.2:3306 1d
myweb 172.17.0.3:8080,172.17.0.4:8080,172.17.0.5:8080 1d
kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes 10.254.0.1 <none> 443/TCP 1d
mysql 10.254.0.5 <none> 3306/TCP 1d
myweb 10.254.220.2 <nodes> 8080:30001/TCP 1d
From the interior of any tomcat container I can see the mysql env and the related mysql link code in JSP is as below:
Class.forName("com.mysql.jdbc.Driver");
String ip=System.getenv("MYSQL_SERVICE_HOST");
String port=System.getenv("MYSQL_SERVICE_PORT");
ip=(ip==null)?"localhost":ip;
port=(port==null)?"3306":port;
System.out.println("Connecting to database...");
conn = java.sql.DriverManager.getConnection("jdbc:mysql://"+ip+":"+port+"?useUnicode=true&characterEncoding=UTF-8", "root","123456");
[root#promote ~]# docker exec -it 1470cfaa1b1c /bin/bash
root#myweb-xswfb:/usr/local/tomcat# env |grep MYSQL_SERVICE
MYSQL_SERVICE_PORT=3306
MYSQL_SERVICE_HOST=mysql
root#myweb-xswfb:/usr/local/tomcat# ping mysql
ping: unknown host
Can someone tell me why I could not ping mysqldb hostname from inner tomcat server?Or how to locate the problem further?

Answer 1

I know the reason, it's the DNS problems. The web server cannot find the IP address of the mysql server. so it failed. Temp solution is change the web server's IP to the mysql db server. Hope can help you. Thank you.

Answer 2

Try to use a Headless Service http://kubernetes.io/v1.0/docs/user-guide/services.html#headless-services
by setting in your mysql Service
clusterIP: None
UPDATE
I have tried your yaml file.
Pods are running:
➜ kb get po
NAME READY STATUS RESTARTS AGE
mysql-ndtxn 1/1 Running 0 7m
myweb-j8xgh 1/1 Running 0 8m
myweb-qc7ws 1/1 Running 0 8m
myweb-zhzll 1/1 Running 0 8m
Services are:
kb get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 1h
mysql ClusterIP 10.102.178.190 <none> 3306/TCP 20m
myweb NodePort 10.98.74.113 <none> 8080:30001/TCP 19m
Endpoints are:
kb get ep
NAME ENDPOINTS AGE
kubernetes 10.0.2.15:8443 1h
mysql 172.17.0.7:3306 20m
myweb 172.17.0.2:8080,172.17.0.4:8080,172.17.0.6:8080 19m
I exec bash on a tomcat pod and I can ping my service (it is resolved):
kb exec -ti myweb-zhzll -- bash
root#myweb-zhzll:/usr/local/tomcat# ping mysql
PING mysql.default.svc.cluster.local (10.102.178.190): 56 data bytes
^C--- mysql.default.svc.cluster.local ping statistics ---
I can ping the endpoint:
ping 172.17.0.7
PING 172.17.0.7 (172.17.0.7): 56 data bytes
64 bytes from 172.17.0.7: icmp_seq=0 ttl=64 time=0.181 ms
64 bytes from 172.17.0.7: icmp_seq=1 ttl=64 time=0.105 ms
64 bytes from 172.17.0.7: icmp_seq=2 ttl=64 time=0.119 ms
^C--- 172.17.0.7 ping statistics ---
Connecting to
http://192.168.99.100:30001/
I can see the tomcat page:
UPDATE 2
Here my screenshot... I see data in your database with no error.
I suggest to check your db configuration.

Answer 3

As a beginner, I did the same work with you and got the same problems.
This is my solution，maybe you can have a try:
Delete these configurations in myweb-rc.yaml, because it will override the system default values:
env:
- name: MYSQL_SERVICE_HOST
value: "mysql"
- name: MYSQL_SERVICE_PORT
value: "3306"
Change the mysql image tag in mysql-rc.yaml. use the low version mysql:
image: hub.c.163.com/library/mysql:5.5
Create the service first, then create the pod. refer to the following sequence:
kubectl create -f myweb-svc.yaml
kubectl create -f mysql-svc.yaml
kubectl create -f mysql-rc.yaml
kubectl create -f myweb-rc.yaml
You can refer to this doc：Discovering services
Good luck!