Kubernetes Architecture Step by Step¶
We will have a overview of k8s architecture through this lab step by step.
Prepare Lab Enviroment¶
We will install kubernetes with Vagrant & CoreOS reference by https://coreos.com/kubernetes/docs/latest/kubernetes-on-vagrant.html.
➜ vagrant git:(master) vagrant status
Current machine states:
e1 running (virtualbox)
c1 running (virtualbox)
w1 running (virtualbox)
w2 running (virtualbox)
w3 running (virtualbox)
This environment represents multiple VMs. The VMs are all listed
above with their current state. For more information about a specific
VM, run `vagrant status NAME`.
One etcd node, one controller node and three worker nodes.
Kubectl version and cluster information
➜ vagrant git:(master) kubectl version
Client Version: version.Info{Major:"1", Minor:"5", GitVersion:"v1.5.1", GitCommit:"82450d03cb057bab0950214ef122b67c83fb11df", GitTreeState:"clean", BuildDate:"2016-12-14T00:57:05Z", GoVersion:"go1.7.4", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"5", GitVersion:"v1.5.1+coreos.0", GitCommit:"cc65f5321f9230bf9a3fa171155c1213d6e3480e", GitTreeState:"clean", BuildDate:"2016-12-14T04:08:28Z", GoVersion:"go1.7.4", Compiler:"gc", Platform:"linux/amd64"}
➜ vagrant git:(master)
➜ vagrant git:(master) kubectl get nodes
NAME STATUS AGE
172.17.4.101 Ready,SchedulingDisabled 32m
172.17.4.201 Ready 32m
172.17.4.202 Ready 32m
172.17.4.203 Ready 32m
➜ vagrant git:(master)
➜ kubernetes-101 git:(master) ✗ kubectl cluster-info
Kubernetes master is running at https://172.17.4.101:443
Heapster is running at https://172.17.4.101:443/api/v1/proxy/namespaces/kube-system/services/heapster
KubeDNS is running at https://172.17.4.101:443/api/v1/proxy/namespaces/kube-system/services/kube-dns
kubernetes-dashboard is running at https://172.17.4.101:443/api/v1/proxy/namespaces/kube-system/services/kubernetes-dashboard
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
➜ kubernetes-101 git:(master) ✗
Get the application we will deploy from github:
$ git clone https://github.com/xiaopeng163/kubernetes-101
This application is a simple python flask web app with a redis server as backend.
Create Pods¶
Use cmd kubectl create to create a pod through a yml file. Firstly, create a redis server pod.
➜ kubernetes-101 git:(master) ✗ cd Kubernetes
➜ Kubernetes git:(master) ✗ ls
db-pod.yml db-svc.yml set.sh web-pod.yml web-rc.yml web-svc.yml
➜ Kubernetes git:(master) ✗
➜ Kubernetes git:(master) ✗ kubectl create -f db-pod.yml
pod "redis" created
➜ Kubernetes git:(master) ✗ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE
redis 1/1 Running 0 1m 10.2.26.2 172.17.4.201
It created a pod which running redis, and the pod is on node w1. We can SSH to this node and check the exactly container created
by kubernetes.
➜ vagrant git:(master) vagrant ssh w1
CoreOS alpha (1164.1.0)
Last login: Mon Jan 9 06:33:50 2017 from 10.0.2.2
core@w1 ~ $ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
7df09a520c43 redis:latest "docker-entrypoint.sh" 19 minutes ago Up 19 minutes k8s_redis.afd331f6_redis_default_b6c27624-d632-11e6-b809-0800274503e1_fb526620
Next, create a web server pod.
➜ Kubernetes git:(master) ✗ kubectl create -f web-pod.yml
pod "web" created
➜ Kubernetes git:(master) ✗ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE
redis 1/1 Running 0 2h 10.2.26.2 172.17.4.201
web 1/1 Running 0 6m 10.2.14.6 172.17.4.203
➜ Kubernetes git:(master) ✗
The web pod is running on node w3.
Create Services¶
Now we have two pods, but they do not know each other. If you SSH to the w3 node which web located on, and access the flask web, it will
return a error.
core@w3 ~ $ curl 10.2.14.6:5000
.....
.....
ConnectionError: Error -2 connecting to redis:6379. Name or service not known.
-->
core@w3 ~ $
The reason is the web pod can not resolve the redis name. We need to create a service.
➜ Kubernetes git:(master) ✗ kubectl create -f db-svc.yml
service "redis" created
➜ Kubernetes git:(master) ✗ kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes 10.3.0.1 <none> 443/TCP 3h
redis 10.3.0.201 <none> 6379/TCP 42s
After that, go to w3 and access the flask web again, it works!
core@w3 ~ $ curl 10.2.14.6:5000
Hello Container World! I have been seen 1 times.
core@w3 ~ $ curl 10.2.14.6:5000
Hello Container World! I have been seen 2 times.
core@w3 ~ $
At last, we need to access the flask web service from the outside of the kubernetes cluster, that need to create another service.
➜ Kubernetes git:(master) ✗ kubectl create -f web-svc.yml
service "web" created
➜ Kubernetes git:(master) ✗
➜ Kubernetes git:(master) ✗ kubectl get svc
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes 10.3.0.1 <none> 443/TCP 3h
redis 10.3.0.201 <none> 6379/TCP 11m
web 10.3.0.51 <nodes> 80:32204/TCP 5s
➜ Kubernetes git:(master) ✗ curl 172.17.4.203:32204
Hello Container World! I have been seen 3 times.
➜ Kubernetes git:(master) ✗
➜ Kubernetes git:(master) ✗ curl 172.17.4.201:32204
Hello Container World! I have been seen 4 times.
➜ Kubernetes git:(master) ✗ curl 172.17.4.202:32204
Hello Container World! I have been seen 5 times.
➜ Kubernetes git:(master) ✗
Now we can access the flask web from the outside, actually from any node.
Scaling Pods with Replication Controller¶
➜ Kubernetes git:(master) ✗ kubectl create -f web-rc.yml
replicationcontroller "web" created
➜ Kubernetes git:(master) ✗ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE
redis 1/1 Running 0 3h 10.2.26.2 172.17.4.201
web 1/1 Running 0 57m 10.2.14.6 172.17.4.203
web-jlzm4 1/1 Running 0 3m 10.2.71.3 172.17.4.202
web-sz150 1/1 Running 0 3m 10.2.26.3 172.17.4.201
➜ Kubernetes git:(master) ✗
Rolling Update¶
To update a service without an outage through rolling update. We will update our flask web container image from 1.0 to 2.0.
➜ kubernetes-101 git:(master) ✗ kubectl get pods
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 6h
web 1/1 Running 0 4h
web-jlzm4 1/1 Running 0 3h
web-sz150 1/1 Running 0 3h
➜ kubernetes-101 git:(master) ✗ kubectl rolling-update web --image=xiaopeng163/docker-flask-demo:2.0
Created web-db65f4ce913c452364a2075625221bec
Scaling up web-db65f4ce913c452364a2075625221bec from 0 to 3, scaling down web from 3 to 0 (keep 3 pods available, do not exceed 4 pods)
Scaling web-db65f4ce913c452364a2075625221bec up to 1
Scaling web down to 2
Scaling web-db65f4ce913c452364a2075625221bec up to 2
Scaling web down to 1
Scaling web-db65f4ce913c452364a2075625221bec up to 3
Scaling web down to 0
Update succeeded. Deleting old controller: web
Renaming web to web-db65f4ce913c452364a2075625221bec
replicationcontroller "web" rolling updated
➜ kubernetes-101 git:(master) ✗ kubectl get pods
NAME READY STATUS RESTARTS AGE
redis 1/1 Running 0 6h
web-db65f4ce913c452364a2075625221bec-130ll 1/1 Running 0 3m
web-db65f4ce913c452364a2075625221bec-85365 1/1 Running 0 4m
web-db65f4ce913c452364a2075625221bec-tsr41 1/1 Running 0 2m
➜ kubernetes-101 git:(master) ✗
After update, check the service.
➜ kubernetes-101 git:(master) ✗ for i in `seq 4`; do curl 172.17.4.203:32204; done
Hello Container World! I have been seen 26 times and my hostname is web-db65f4ce913c452364a2075625221bec-130ll.
Hello Container World! I have been seen 27 times and my hostname is web-db65f4ce913c452364a2075625221bec-85365.
Hello Container World! I have been seen 28 times and my hostname is web-db65f4ce913c452364a2075625221bec-130ll.
Hello Container World! I have been seen 29 times and my hostname is web-db65f4ce913c452364a2075625221bec-130ll.
➜ kubernetes-101 git:(master) ✗
We can see it automatically load balanced.
Clear Environment¶
$ kubectl delete services web
$ kubectl delete services redis
$ kubectl delete rc web
$ kubectl delete pod redis
$ kubectl delete pod web