使用Deployment运行一个无状态应用

本文介绍通过Kubernetes Deployment对象如何去运行一个应用.

教程目标

  • 创建一个nginx deployment.
  • 使用kubectl列举关于deployment信息.
  • 更新deployment.

准备开始

你必须拥有一个 Kubernetes 的集群，同时你的 Kubernetes 集群必须带有 kubectl 命令行工具。 如果你还没有集群，你可以通过 Minikube 构建一 个你自己的集群，或者你可以使用下面任意一个 Kubernetes 工具构建：

要获知版本信息，请输入 kubectl version.

创建和探究一个nginx deployment

你可以通过创建一个Kubernetes Deployment对象来运行一个应用, 可以在一个YAML文件中描述Deployment. 例如, 下面这个YAML文件描述了一个运行nginx:1.7.9 Docker镜像的Deployment:

application/deployment.yaml 使用Deployment运行一个无状态应用 - 图1
  1. apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
  2. kind: Deployment
  3. metadata:
  4.   name: nginx-deployment
  5. spec:
  6.   selector:
  7.     matchLabels:
  8.       app: nginx
  9.   replicas: 2 # tells deployment to run 2 pods matching the template
  10.   template:
  11.     metadata:
  12.       labels:
  13.         app: nginx
  14.     spec:
  15.       containers:
  16.       - name: nginx
  17.         image: nginx:1.14.2
  18.         ports:
  19.         - containerPort: 80

  1. 通过YAML文件创建一个Deployment:

    1. kubectl apply -f https://k8s.io/examples/application/deployment.yaml

  2. 展示Deployment相关信息:

    kubectl describe deployment nginx-deployment

    1. user@computer:~/website$ kubectl describe deployment nginx-deployment
    2. Name:     nginx-deployment
    3. Namespace:    default
    4. CreationTimestamp:  Tue, 30 Aug 2016 18:11:37 -0700
    5. Labels:     app=nginx
    6. Annotations:    deployment.kubernetes.io/revision=1
    7. Selector:   app=nginx
    8. Replicas:   2 desired | 2 updated | 2 total | 2 available | 0 unavailable
    9. StrategyType:   RollingUpdate
    10. MinReadySeconds:  0
    11. RollingUpdateStrategy:  1 max unavailable, 1 max surge
    12. Pod Template:
    13.   Labels:       app=nginx
    14.   Containers:
    15.    nginx:
    16.     Image:              nginx:1.7.9
    17.     Port:               80/TCP
    18.     Environment:        <none>
    19.     Mounts:             <none>
    20.   Volumes:              <none>
    21. Conditions:
    22.   Type          Status  Reason
    23.   ----          ------  ------
    24.   Available     True    MinimumReplicasAvailable
    25.   Progressing   True    NewReplicaSetAvailable
    26. OldReplicaSets:   <none>
    27. NewReplicaSet:    nginx-deployment-1771418926 (2/2 replicas created)
    28. No events.

  3. 列出deployment创建的pods:

    kubectl get pods -l app=nginx

    1. NAME                                READY     STATUS    RESTARTS   AGE
    2. nginx-deployment-1771418926-7o5ns   1/1       Running   0          16h
    3. nginx-deployment-1771418926-r18az   1/1       Running   0          16h

  4. 展示某一个pod信息:

    kubectl describe pod

    该处 <pod-name> 指某一pod的名称.

更新deployment

你可以通过更新一个新的YAML文件来更新deployment. 下面的YAML文件指定该deployment镜像更新为nginx 1.8.

application/deployment-update.yaml 使用Deployment运行一个无状态应用 - 图2
  1. apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
  2. kind: Deployment
  3. metadata:
  4.   name: nginx-deployment
  5. spec:
  6.   selector:
  7.     matchLabels:
  8.       app: nginx
  9.   replicas: 2
  10.   template:
  11.     metadata:
  12.       labels:
  13.         app: nginx
  14.     spec:
  15.       containers:
  16.       - name: nginx
  17.         image: nginx:1.16.1 # Update the version of nginx from 1.14.2 to 1.16.1
  18.         ports:
  19.         - containerPort: 80

  1. 应用新的YAML:

    1.  kubectl apply -f https://k8s.io/examples/application/deployment-update.yaml

  2. 查看该deployment创建的pods以新的名称同时删除旧的pods:

    1.  kubectl get pods -l app=nginx

通过增加副本数来弹缩应用

你可以通过应用新的YAML文件来增加Deployment中pods的数量. 该YAML文件将replicas设置为4, 指定该Deployment应有4个pods:

application/deployment-scale.yaml 使用Deployment运行一个无状态应用 - 图3
  1. apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
  2. kind: Deployment
  3. metadata:
  4.   name: nginx-deployment
  5. spec:
  6.   selector:
  7.     matchLabels:
  8.       app: nginx
  9.   replicas: 4 # Update the replicas from 2 to 4
  10.   template:
  11.     metadata:
  12.       labels:
  13.         app: nginx
  14.     spec:
  15.       containers:
  16.       - name: nginx
  17.         image: nginx:1.14.2
  18.         ports:
  19.         - containerPort: 80

  1. 应用新的YAML文件:

    1. kubectl apply -f https://k8s.io/examples/application/deployment-scale.yaml

  2. 验证Deployment有4个pods:

    1. kubectl get pods -l app=nginx

    输出的结果类似于:

    1. NAME                               READY     STATUS    RESTARTS   AGE
    2. nginx-deployment-148880595-4zdqq   1/1       Running   0          25s
    3. nginx-deployment-148880595-6zgi1   1/1       Running   0          25s
    4. nginx-deployment-148880595-fxcez   1/1       Running   0          2m
    5. nginx-deployment-148880595-rwovn   1/1       Running   0          2m

删除deployment

通过名称删除deployment:

  1. kubectl delete deployment nginx-deployment

ReplicationControllers — 旧的方式

创建一个多副本应用首选方法是使用Deployment,反过来使用ReplicaSet. 在Deployment和ReplicaSet加入到Kubernetes之前, 多副本应用通过ReplicationController来配置.

接下来