在kubernetes中运行单节点有状态MySQL应用

Deploy MySQL

https://kubernetes.io/docs/tasks/run-application/run-single-instance-stateful-application/

You can run a stateful application by creating a Kubernetes Deployment and connecting it to an existing PersistentVolume using a PersistentVolumeClaim. For example, this YAML file describes a Deployment that runs MySQL and references the PersistentVolumeClaim. The file defines a volume mount for /var/lib/mysql, and then creates a PersistentVolumeClaim that looks for a 20G volume. This claim is satisfied by any existing volume that meets the requirements, or by a dynamic provisioner.

Note: The password is defined in the config yaml, and this is insecure. See Kubernetes Secrets for a secure solution.

application/mysql/mysql-deployment.yaml 

apiVersion: v1
kind: Service
metadata:
  name: mysql
spec:
  ports:
  - port: 3306
  selector:
    app: mysql
  clusterIP: None
---
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: mysql
spec:
  selector:
    matchLabels:
      app: mysql
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - image: mysql:5.6
        name: mysql
        env:
          # Use secret in real usage
        - name: MYSQL_ROOT_PASSWORD
          value: password
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pv-claim

application/mysql/mysql-pv.yaml 

kind: PersistentVolume
apiVersion: v1
metadata:
  name: mysql-pv-volume
  labels:
    type: local
spec:
  storageClassName: manual
  capacity:
    storage: 20Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: "/mnt/data"
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-pv-claim
spec:
  storageClassName: manual
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi

• 现成的kubernetes集群
• 持久存储-PersistentVolume
• 持久存储容量声明-PersistentVolumeClaim

k8s不会真正检查存储的访问模式或根据访问模式做访问限制，只是对真实存储的描述，最终的控制权在真实的存储端。目前支持三种访问模式：

• ReadWriteOnce – PV以read-write 挂载到一个节点
• ReadWriteMany – PV以read-write 方式挂载到多个节点
• ReadOnlyMany – PV以read-only 方式挂载到多个节点

1. Deploy the PV and PVC of the YAML file:

   kubectl create -f https://k8s.io/examples/application/mysql/mysql-pv.yaml
   

2. Deploy the contents of the YAML file:

   kubectl create -f https://k8s.io/examples/application/mysql/mysql-deployment.yaml
   

3. Display information about the Deployment:

   kubectl describe deployment mysql
   
   Name:                 mysql
   Namespace:            default
   CreationTimestamp:    Tue, 01 Nov 2016 11:18:45 -0700
   Labels:               app=mysql
   Annotations:          deployment.kubernetes.io/revision=1
   Selector:             app=mysql
   Replicas:             1 desired | 1 updated | 1 total | 0 available | 1 unavailable
   StrategyType:         Recreate
   MinReadySeconds:      0
   Pod Template:
     Labels:       app=mysql
     Containers:
      mysql:
       Image:      mysql:5.6
       Port:       3306/TCP
       Environment:
         MYSQL_ROOT_PASSWORD:      password
       Mounts:
         /var/lib/mysql from mysql-persistent-storage (rw)
     Volumes:
      mysql-persistent-storage:
       Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
       ClaimName:  mysql-pv-claim
       ReadOnly:   false
   Conditions:
     Type          Status  Reason
     ----          ------  ------
     Available     False   MinimumReplicasUnavailable
     Progressing   True    ReplicaSetUpdated
   OldReplicaSets:       <none>
   NewReplicaSet:        mysql-63082529 (1/1 replicas created)
   Events:
     FirstSeen    LastSeen    Count    From                SubobjectPath    Type        Reason            Message
     ---------    --------    -----    ----                -------------    --------    ------            -------
     33s          33s         1        {deployment-controller }             Normal      ScalingReplicaSet Scaled up replica set mysql-63082529 to 1
   

4. List the pods created by the Deployment:

   kubectl get pods -l app=mysql
   
   NAME                   READY     STATUS    RESTARTS   AGE
   mysql-63082529-2z3ki   1/1       Running   0          3m
   

5. Inspect the PersistentVolumeClaim:

   kubectl describe pvc mysql-pv-claim
   
   Name:         mysql-pv-claim
   Namespace:    default
   StorageClass:
   Status:       Bound
   Volume:       mysql-pv-volume
   Labels:       <none>
   Annotations:    pv.kubernetes.io/bind-completed=yes
                   pv.kubernetes.io/bound-by-controller=yes
   Capacity:     20Gi
   Access Modes: RWO
   Events:       <none>
   

Accessing the MySQL instance

The preceding YAML file creates a service that allows other Pods in the cluster to access the database. The Service option clusterIP: None lets the Service DNS name resolve directly to the Pod’s IP address. This is optimal when you have only one Pod behind a Service and you don’t intend to increase the number of Pods.

Run a MySQL client to connect to the server:

kubectl run -it --rm --image=mysql:5.6 --restart=Never mysql-client -- mysql -h mysql -ppassword

This command creates a new Pod in the cluster running a MySQL client and connects it to the server through the Service. If it connects, you know your stateful MySQL database is up and running.

Waiting for pod default/mysql-client-274442439-zyp6i to be running, status is Pending, pod ready: false
If you don't see a command prompt, try pressing enter.

mysql>

Updating

The image or any other part of the Deployment can be updated as usual with the kubectl apply command. Here are some precautions that are specific to stateful apps:

• Don’t scale the app. This setup is for single-instance apps only. The underlying PersistentVolume can only be mounted to one Pod. For clustered stateful apps, see the StatefulSet documentation.
• Use strategy: type: Recreate in the Deployment configuration YAML file. This instructs Kubernetes to not use rolling updates. Rolling updates will not work, as you cannot have more than one Pod running at a time. The Recreate strategy will stop the first pod before creating a new one with the updated configuration.

Deleting a deployment

Delete the deployed objects by name:

kubectl delete deployment,svc mysql
kubectl delete pvc mysql-pv-claim
kubectl delete pv mysql-pv-volume

If you manually provisioned a PersistentVolume, you also need to manually delete it, as well as release the underlying resource. If you used a dynamic provisioner, it automatically deletes the PersistentVolume when it sees that you deleted the PersistentVolumeClaim. Some dynamic provisioners (such as those for EBS and PD) also release the underlying resource upon deleting the PersistentVolume.

What's next