It’s necessary to use external storage if you’d like to use Persistent Data.

For exmaple, Create a Pod with mounting external storage which is mapped with a directory for saving data on the Node Pod runs. The environment and Container image on this exmaple are the same with here.

Container image for exmaples

For example, Create a Dockerfile to install httpd and add index.html, and also start httpd with 80 port.

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# create a Dockerfile
[root@kubernetes-controller ~]# vi Dockerfile
FROM centos
MAINTAINER serverworld <admin@itweet.cn>
RUN yum -y install httpd
RUN echo "Hello DockerFile by itweet.cn" > /var/www/html/index.html
EXPOSE 80
CMD ["-D", "FOREGROUND"]
ENTRYPOINT ["/usr/sbin/httpd"]

# build image ⇒ docker build -t [image name]:[tag] .
[root@kubernetes-controller ~]# docker build -t apache_server:latest ./Dockerfile
unable to prepare context: context must be a directory: /root/Dockerfile
[root@kubernetes-controller ~]# docker build -t apache_server:latest .
Sending build context to Docker daemon 948.7 kB
Step 1 : FROM centos
---> 970633036444
Step 2 : MAINTAINER serverworld <admin@itweet.cn>
---> Running in 7f20b2eff551
---> 8041da7bcf1a
Removing intermediate container 7f20b2eff551
Step 3 : RUN yum -y install httpd
---> Running in 81073cca988b
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
* base: mirrors.tuna.tsinghua.edu.cn
* extras: mirrors.tuna.tsinghua.edu.cn
* updates: mirror.bit.edu.cn
Resolving Dependencies
...
...
Step 7 : ENTRYPOINT /usr/sbin/httpd
---> Running in 16fa3fcd76dc
---> d165379a81f0
Removing intermediate container 16fa3fcd76dc
Successfully built d165379a81f0

[root@kubernetes-controller ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
apache_server latest d165379a81f0 52 seconds ago 321.9 MB
docker.io/centos latest 970633036444 2 weeks ago 196.7 MB

[root@kubernetes-controller ~]# docker run -d -p 80:80 apache_server
505d10f894084e1ea417091f6adbe44a7d8df8c7518c5c5dd3ddce1c5f0ed05f

[root@kubernetes-controller ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
505d10f89408 apache_server "/usr/sbin/httpd -D F" 14 seconds ago Up 13 seconds 0.0.0.0:80->80/tcp pensive_bhaskara

[root@kubernetes-controller ~]# curl http://localhost/
Hello DockerFile by itweet.cn

Container image loads to All Nodes

[1] Copy a container image just created above to all other Nodes like follows.

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# output container image to a file
[root@kubernetes-controller ~]# docker save apache_server > apache_server.tar

# copy the image to other Nodes
[root@kubernetes-controller ~]# scp apache_server.tar kubernetes-node-1:/root/
...
...
[root@kubernetes-controller ~]# scp apache_server.tar kubernetes-node-3:/root/

[2] Load the comtainer image just copied.

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[root@kubernetes-node-1 ~]# docker load < apache_server.tar 
[root@kubernetes-node-1 ~]# docker images apache_server
REPOSITORY TAG IMAGE ID CREATED SIZE
apache_server latest d165379a81f0 8 minutes ago 321.9 MB

关于kubernetes创建pod时,使用的镜像本地已经存在,但还一直在下载。如何create pod时可以跨过下载这一步,直接使用本地镜像?
http://dockone.io/question/1075

Create a httpd Pods

[1] Admin Node.

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[root@kubernetes-controller ~]# cat pod-httpd.yaml 
apiVersion: v1
kind: Pod
metadata:
name: apache-httpd
spec:
containers:
- name: apache-httpd
image: httpd
ports:
- containerPort: 80
volumeMounts:
# the volume to use (it's the one defined in "volumes" section)
- name: httpd-storage
# mount point inside Container
mountPath: /var/www/html
volumes:
# any name you like
- name: httpd-storage
hostPath:
# the directory on Host Node for saving data
path: /tmp/httpd

[root@kubernetes-controller ~]# kubectl create -f pod-httpd.yaml
pod "apache-httpd" created

[root@kubernetes-controller ~]# kubectl get pods -o wide |grep apache-httpd
apache-httpd 0/1 ContainerCreating 0 27s kubernetes-node-3

[root@kubernetes-controller ~]# kubectl get pod apache-httpd -o yaml | grep "podIP"
podIP: 172.16.45.5

[2] Move to a Node that Pod is running and make sure to work normally.

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[root@kubernetes-node-3 ~]# curl http://172.16.45.5/
<html><body><h1>It works!</h1></body></html>

[root@kubernetes-node-3 ~]# echo "Kubernetes Persistent Storage && www.itweet.cn" > /tmp/httpd/index.html

-- enter to a running container,look at volume mapping bit sucess

[root@kubernetes-node-3 ~]# nsenter --target 24207 --mount --uts --ipc --net --pid
root@apache-httpd:/#

[root@kubernetes-node-3 ~]# docker inspect -f '{{.State.Pid}}' b92a2432f8d2
24207
[root@kubernetes-node-3 ~]# nsenter --target 24207 --mount --uts --ipc --net --pid
root@apache-httpd:/# ls /var/www/html/
index.html
root@apache-httpd:/# cat /var/www/html/index.html
Kubernetes Persistent Storage && www.itweet.cn

-- not found , my self wirte content. because official httpd images "DocumentRoot" configuration is "/usr/local/apache2/htdocs/index.html"

root@apache-httpd:/usr/local/apache2/conf# cat /usr/local/apache2/htdocs/index.html
<html><body><h1>It works!</h1></body></html>
root@apache-httpd:/usr/local/apache2/conf# ls /usr/local/apache2/htdocs/index.html -l
-rw-r--r--. 1 501 staff 45 Jun 11 2007 /usr/local/apache2/htdocs/index.html

This is kubernetes persistent storage,Host Machine install Distributed ceph or glusterfs in back-end storage.

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