Kubernetes使用Ceph静态卷部署应用

[TOC]

1. kubernetes 中的存储方案

对于有状态服务，存储是一个至关重要的问题。k8s提供了非常丰富的组件来支持存储，这里大致列一下：

• volume: 就是直接挂载在pod上的组件，k8s中所有的其他存储组件都是通过volume来跟pod直接联系的。volume有个type属性，type决定了挂载的存储是什么，常见的比如：emptyDir，hostPath，nfs，rbd，以及下文要说的persistentVolumeClaim等。跟docker里面的volume概念不同的是，docker里的volume的生命周期是跟docker紧紧绑在一起的。这里根据type的不同，生命周期也不同，比如emptyDir类型的就是跟docker一样，pod挂掉，对应的volume也就消失了，而其他类型的都是永久存储。详细介绍可以参考Volumes
• Persistent Volumes：顾名思义，这个组件就是用来支持永久存储的，Persistent Volumes组件会抽象后端存储的提供者（也就是上文中volume中的type）和消费者（即具体哪个pod使用）。该组件提供了PersistentVolume和PersistentVolumeClaim两个概念来抽象上述两者。一个PersistentVolume（简称PV）就是后端存储提供的一块存储空间，具体到ceph rbd中就是一个image，一个PersistentVolumeClaim（简称PVC）可以看做是用户对PV的请求，PVC会跟某个PV绑定，然后某个具体pod会在volume 中挂载PVC,就挂载了对应的PV。关于更多详细信息比如PV,PVC的生命周期，dockerfile 格式等信息参考Persistent Volumes
• Dynamic Volume Provisioning: 动态volume发现，比如上面的Persistent Volumes,我们必须先要创建一个存储块，比如一个ceph中的image，然后将该image绑定PV，才能使用。这种静态的绑定模式太僵硬，每次申请存储都要向存储提供者索要一份存储快。Dynamic Volume Provisioning就是解决这个问题的。它引入了StorageClass这个概念，StorageClass抽象了存储提供者，只需在PVC中指定StorageClass，然后说明要多大的存储就可以了，存储提供者会根据需求动态创建所需存储快。甚至于，我们可以指定一个默认StorageClass，这样，只需创建PVC就可以了。

2. 环境准备

可用的kubernetes
可用的Ceph集群
Ceph monitor节点：lab1、lab2、lab3

# k8s
192.168.105.92 lab1 # master1
192.168.105.93 lab2 # master2
192.168.105.94 lab3 # master3
192.168.105.95 lab4 # node4
192.168.105.96 lab5 # node5
192.168.105.97 lab6 # node6
192.168.105.98 lab7 # node7

在每个k8s node中安装yum install -y ceph-common

3. CephFS方式部署容器

3.1 创建Ceph admin secret

ceph auth get-key client.admin > /tmp/secret
kubectl create namespace cephfs
kubectl create secret generic ceph-admin-secret --from-file=/tmp/secret

3.2 创建pv

vim cephfs-pv.yaml

apiVersion: v1
kind: PersistentVolume
metadata:
  name: cephfs-pv1
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteMany
  cephfs:
    monitors:
      - 192.168.105.92:6789
      - 192.168.105.93:6789
      - 192.168.105.94:6789
    user: admin
    secretRef:
      name: ceph-admin-secret
    readOnly: false
  persistentVolumeReclaimPolicy: Recycle

3.3 创建pvc

vim cephfs-pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: cephfs-pv-claim1
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 1Gi

3.4 部署验证

vim cephfs-nginx.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-cephfs
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 80
          volumeMounts:
            - name: ceph-cephfs-volume
              mountPath: "/usr/share/nginx/html"
      volumes:
      - name: ceph-cephfs-volume
        persistentVolumeClaim:
          claimName: cephfs-pv-claim1

kubectl create -f cephfs-pv.yaml
kubectl create -f cephfs-pvc.yaml
kubectl create -f cephfs-nginx.yaml

验证结果：

[root@lab1 cephfs]# kubectl get pv
NAME         CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                      STORAGECLASS   REASON    AGE
cephfs-pv1   1Gi        RWX            Recycle          Bound     default/cephfs-pv-claim1                            1h
[root@lab1 cephfs]# kubectl get pvc     
NAME               STATUS    VOLUME       CAPACITY   ACCESS MODES   STORAGECLASS   AGE
cephfs-pv-claim1   Bound     cephfs-pv1   1Gi        RWX                           1h
test-pvc           Bound     test-pv      1Gi        RWO                           32m
[root@lab1 cephfs]# kubectl get pod |grep nginx-cephfs
nginx-cephfs-7777495b9b-29vtw       1/1       Running             0          13m
[root@lab1 cephfs]# kubectl exec -it nginx-cephfs-7777495b9b-29vtw -- df -h|grep nginx
192.168.105.92:6789:/  1.6T  4.1G  1.6T   1% /usr/share/nginx/html

4. RBD方式部署容器

4.1 创建Ceph admin secret

ceph auth get-key client.admin > /tmp/secret
kubectl create namespace cephfs
kubectl create secret generic ceph-admin-secret --from-file=/tmp/secret

4.2 创建Ceph pool 和Image

ceph osd pool create kube 128 128
rbd create kube/foo -s 10G --image-feature layering

4.3 创建pv

vim rbd-pv.yaml

apiVersion: v1
kind: PersistentVolume
metadata:
  name: rbd-pv1
spec:
  capacity:
    storage: 1Gi
  accessModes:
    - ReadWriteOnce 
  rbd:
    monitors:
      - 192.168.105.92:6789
      - 192.168.105.93:6789
      - 192.168.105.94:6789
    pool: kube
    image: foo
    user: admin
    secretRef:
      name: ceph-secret
  persistentVolumeReclaimPolicy: Recycle

4.4 创建pvc

vim rbd-pvc.yaml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: rbd-pv-claim1
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

4.5 部署验证

vim rbd-nginx.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-rbd
spec:
  replicas: 1
  template:
    metadata:
      labels:
        name: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 80
          volumeMounts:
            - name: ceph-rbd-volume
              mountPath: "/usr/share/nginx/html"
      volumes:
      - name: ceph-rbd-volume
        persistentVolumeClaim:
          claimName: rbd-pv-claim1

kubectl create -f rbd-pv.yaml
kubectl create -f rbd-pvc.yaml
kubectl create -f rbd-nginx.yaml

验证结果：

[root@lab1 rbd]# kubectl get pv
NAME         CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                      STORAGECLASS   REASON    AGE
cephfs-pv1   1Gi        RWX            Recycle          Bound     default/cephfs-pv-claim1                            2h
rbd-pv1      5Gi        RWO            Recycle          Bound     default/rbd-pv-claim1                               8m
[root@lab1 rbd]# kubectl get pvc
NAME               STATUS    VOLUME       CAPACITY   ACCESS MODES   STORAGECLASS   AGE
cephfs-pv-claim1   Bound     cephfs-pv1   1Gi        RWX                           2h
claim2             Pending                                          rbd            2h
claim3             Pending                                          rbd            2h
rbd-pv-claim1      Bound     rbd-pv1      5Gi        RWO                           8m
[root@lab1 rbd]# kubectl exec -it nginx-rbd-6b555f58c9-7k2k9 -- df -h|grep nginx
/dev/rbd0            9.8G   37M  9.7G   1% /usr/share/nginx/html

进入容器使用dd测试，发现容器容易挂。而且经过验证，容器挂载的目录大小取决于rbd image的大小
dd if=/dev/zero of=/usr/share/nginx/html/test.data bs=1G count=8 &

root@nginx-rbd-6b555f58c9-7k2k9:/usr/share/nginx/html# error: Internal error occurred: error executing command in container: Error response from daemon: Container 12f9c29c03082d27c7ed4327536626189d02be451029f7385765d3c2e1451062 is not running: Exited (0) Less than a second ago

参考资料：
[1] https://kubernetes.io/docs/concepts/storage/volumes/
[2] https://kubernetes.io/docs/concepts/storage/persistent-volumes/
[3] https://zhangchenchen.github.io/2017/11/17/kubernetes-integrate-with-ceph/