RunYourAppOnK8S

1. You want to run a APP jenkins

Jenkins Docker Image: jenkins/jenkins:lts

(https://hub.docker.com/r/jenkins/jenkins)

Jenkins Serving port: 8080 adn 50000

(https://github.com/istresearch/jenkins/blob/master/README.md)
-p 8080:8080 so the 8080 port in the container receives all requests to port 8080 on the host. Jenkins runs on Tomcat, which uses port 8080 as the default
-p 5000:5000 required to attach slave servers; port 50000 is used to communicate between master and slaves

Jenkins Home dir: /var/jenkins_home

(https://www.jenkins.io/doc/book/installing/#accessing-the-jenkins-home-directory)
Map the home dir to the volumes, then you can access and check the contents of the Jenkins App

2. Create a jenkins deployment

A jenkins deployment only supports one replica because jenkins home can only be read/wrote by one jenkins master
A jenkins deployment spec has container iamge: jenkins/jenkins:lts
A jenkins deployment spec has containers ports: 8080 and 50000
A jenkins deployment spec has container volume mount: /var/jenkins_home

kubectl apply -f deployment.yaml

A deployment creation brings a replicaset created automatically.

3. Create a persistent volume claim for jenkins

create a managed-fns-storage (TODO)

create a pvc

kubectl apply -f pvc.yaml

4. Create a service for jenkins

kubectl apply -f service.yaml

A service helps discover the endpoints as backend servers.

5. Create an ingress for jenkins

create ingress controller (TODO)

create ingress

kubectl apply -f ingress.yaml

6. Access jenkins

6.1 Access jenkins from jenkins pod

get the pod IP

[root@vxlan-vm-111-38 jenkins-k8s]# kubectl get pod -owide
NAME                                      READY   STATUS      RESTARTS   AGE     IP          NODE              NOMINATED NODE   READINESS GATES
jenkins-deployment-687ffcd9c4-7fmpf       1/1     Running     0          7h14m   10.2.1.22   vxlan-vm-111-4    <none>           <none>

curl pod IP with the container ports (works from each node since pod is reachable inside a cluster):

[root@vxlan-vm-111-38 jenkins-k8s]# curl http://10.2.1.22:8080
<html><head><meta http-equiv='refresh' content='1;url=/login?from=%2F'/><script>window.location.replace('/login?from=%2F');</script></head><body style='background-color:white; color:white;'>


Authentication required
<!--
You are authenticated as: anonymous
Groups that you are in:
  
Permission you need to have (but didn't): hudson.model.Hudson.Read
 ... which is implied by: hudson.security.Permission.GenericRead
 ... which is implied by: hudson.model.Hudson.Administer
-->

</body></html>

and

[root@vxlan-vm-111-38 jenkins-k8s]# curl http://10.2.1.22:50000
Jenkins-Agent-Protocols: JNLP4-connect, Ping
Jenkins-Version: 2.222.3
Jenkins-Session: 966a9424
Client: 10.2.0.0
Server: 10.2.1.22
Remoting-Minimum-Version: 3.14

6.2 Access jenkins from jenkins service

get the svc cluster IP

[root@vxlan-vm-111-38 jenkins-k8s]# kubectl get svc
NAME                     TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)            AGE
jenkins-master-service   ClusterIP   10.1.128.125   <none>        80/TCP,50000/TCP   7h16m

curl the cluster IP with cluster ports (works from each node):

[root@vxlan-vm-111-38 jenkins-k8s]# curl  http://10.1.128.125:80
<html><head><meta http-equiv='refresh' content='1;url=/login?from=%2F'/><script>window.location.replace('/login?from=%2F');</script></head><body style='background-color:white; color:white;'>


Authentication required
<!--
You are authenticated as: anonymous
Groups that you are in:
  
Permission you need to have (but didn't): hudson.model.Hudson.Read
 ... which is implied by: hudson.security.Permission.GenericRead
 ... which is implied by: hudson.model.Hudson.Administer
-->

</body></html>

and

[root@vxlan-vm-111-38 jenkins-k8s]# curl  http://10.1.128.125:50000
Jenkins-Agent-Protocols: JNLP4-connect, Ping
Jenkins-Version: 2.222.3
Jenkins-Session: 966a9424
Client: 10.2.0.0
Server: 10.2.1.22
Remoting-Minimum-Version: 3.14

The reason we can reach cluster IP from each node:
kube-ipvs0 inets are created on each node:

kube-ipvs0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default 
    link/ether 82:3c:2e:25:d1:19 brd ff:ff:ff:ff:ff:ff
    inet 10.1.0.1/32 brd 10.1.0.1 scope global kube-ipvs0
       valid_lft forever preferred_lft forever
    inet 10.1.0.10/32 brd 10.1.0.10 scope global kube-ipvs0
       valid_lft forever preferred_lft forever
    inet 10.1.77.75/32 brd 10.1.77.75 scope global kube-ipvs0
       valid_lft forever preferred_lft forever
    inet 10.1.24.217/32 brd 10.1.24.217 scope global kube-ipvs0
       valid_lft forever preferred_lft forever
    inet 10.1.128.125/32 brd 10.1.128.125 scope global kube-ipvs0
       valid_lft forever preferred_lft forever

and rules are created on each node:

[root@vxlan-vm-111-38 jenkins-k8s]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
...
TCP  10.1.128.125:80 rr
  -> 10.2.1.22:8080               Masq    1      0          0         
TCP  10.1.128.125:50000 rr
  -> 10.2.1.22:50000              Masq    1      0          0         
...

6.3 Access jenkins from jenkins ingress

6.3.1 Add DNS entry. Eg in /etc/hosts

192.168.111.15 jenkins.example.com

(node IP which ingress controller runs on / jenkins ingress rules host)

note: I have used an nimubs isolated env which has a jumper. I need to add entry in /etc/hosts and also configure /etc/squid/squid.conf to make sure jenkins.example.com can be resoved from browser

6.3.2 Curl it

curl -H 'Host: jenkins.example.com' http://192.168.111.15

192.168.111.15 is the node IP which ingress controller runs on

6.4 Access from browser (final goal)

Input http://jenkins.example.com or jenkins.example.com or jenkins.example.com:80 in browser and go
note: If jenkins.example.com, browser will complement to http://jenkins.example.com:80 by default (add http:// as prefix and suffix :80)

wyike / RunYourAppOnK8S