k8s(Kubernetes)中Pod,Deployment,ReplicaSet,Service之间关系分析

看完k8s文档，好多概念似乎明白了，又似乎不明白，多个概念之间的关系也很混乱，不是很明白，不要紧，接下来，好好分析一下。结论您有可能在急着找答案搜到我这篇文章，不费话，结论就在开头，请看下图。deploy控制RS，RS控制Pod，这一整套，向外提供稳定可靠的Service。分析以下是分析的过程首先，我们先从最小的调度单位pod开始。我的k8s集群中目前有一个pod，它...

ucsheep

26809人浏览 · 2018-08-17 18:50:45

ucsheep · 2018-08-17 18:50:45 发布

看完k8s文档，好多概念似乎明白了，又似乎不明白，多个概念之间的关系也很混乱，不是很明白，不要紧，接下来，好好分析一下。

结论

您有可能在急着找答案搜到我这篇文章，不费话，结论就在开头，请看下图。

deploy控制RS，RS控制Pod，这一整套，向外提供稳定可靠的Service。

分析

以下是分析的过程

首先，我们先从最小的调度单位pod开始。

我的k8s集群中目前有一个pod，它的name为mq-svc-5b96bf78d9-brpjw

[root@VM_0_17_centos ~]# kubectl get pods
NAME                      READY     STATUS    RESTARTS   AGE
mq-svc-5b96bf78d9-brpjw   1/1       Running   0          51m

来看一下它的详情

[root@VM_0_17_centos ~]# kubectl describe pod mq-svc-5b96bf78d9-brpjw
Name:           mq-svc-5b96bf78d9-brpjw
Namespace:      default
Node:           10.0.0.17/10.0.0.17
Start Time:     Fri, 17 Aug 2018 17:24:44 +0800
Labels:         pod-template-hash=1652693485
                qcloud-app=mq-svc
Annotations:    <none>
Status:         Running
IP:             172.16.0.39
Controlled By:  ReplicaSet/mq-svc-5b96bf78d9
Containers:
  queue-mq:
    Container ID:   docker://700cdc55c111a413faaa8cabb8680009d2663701ccbe84b8a50ea6e6fe1d538c
    Image:          rabbitmq:management
    Image ID:       docker-pullable://rabbitmq@sha256:0b36ea1a8df9e53228aaeee277680de2cc97c7d675bc2d5dbe1cc9e3836a9d9f
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Fri, 17 Aug 2018 17:24:49 +0800
    Ready:          True
    Restart Count:  0
    Limits:
      cpu:     500m
      memory:  1Gi
    Requests:
      cpu:        250m
      memory:     256Mi
    Environment:  <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-vzhz4 (ro)
Conditions:
  Type           Status
  Initialized    True 
  Ready          True 
  PodScheduled   True 
Volumes:
  default-token-vzhz4:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-vzhz4
    Optional:    false
QoS Class:       Burstable
Node-Selectors:  <none>
Tolerations:     <none>
Events:
  Type    Reason                 Age   From                Message
  ----    ------                 ----  ----                -------
  Normal  Scheduled              51m   default-scheduler   Successfully assigned mq-svc-5b96bf78d9-brpjw to 10.0.0.17
  Normal  SuccessfulMountVolume  51m   kubelet, 10.0.0.17  MountVolume.SetUp succeeded for volume "default-token-vzhz4"
  Normal  Pulling                51m   kubelet, 10.0.0.17  pulling image "rabbitmq:management"
  Normal  Pulled                 51m   kubelet, 10.0.0.17  Successfully pulled image "rabbitmq:management"
  Normal  Created                51m   kubelet, 10.0.0.17  Created container
  Normal  Started                51m   kubelet, 10.0.0.17  Started container

其实有一个敏感的信息，pod是被一个名字为mq-svc-5b96bf78d9的ReplicaSet管理的，所以我们认为，RS是比Pod高一级别的专门用来管理pod的组件。一个RS会管理一批pod。

Controlled By:  ReplicaSet/mq-svc-5b96bf78d9

而且在pod里面发生的实践也都是对容器的操作，比如拉取镜像、启动容器等等

Events:
  Type    Reason                 Age   From                Message
  ----    ------                 ----  ----                -------
  Normal  Scheduled              51m   default-scheduler   Successfully assigned mq-svc-5b96bf78d9-brpjw to 10.0.0.17
  Normal  SuccessfulMountVolume  51m   kubelet, 10.0.0.17  MountVolume.SetUp succeeded for volume "default-token-vzhz4"
  Normal  Pulling                51m   kubelet, 10.0.0.17  pulling image "rabbitmq:management"
  Normal  Pulled                 51m   kubelet, 10.0.0.17  Successfully pulled image "rabbitmq:management"
  Normal  Created                51m   kubelet, 10.0.0.17  Created container
  Normal  Started                51m   kubelet, 10.0.0.17  Started container

接下来，我们就看看这个RS的详细情况

[root@VM_0_17_centos ~]# kubectl describe rs mq-svc-5b96bf78d9
Name:           mq-svc-5b96bf78d9
Namespace:      default
Selector:       pod-template-hash=1652693485,qcloud-app=mq-svc
Labels:         pod-template-hash=1652693485
                qcloud-app=mq-svc
Annotations:    deployment.changecourse=Updating
                deployment.kubernetes.io/desired-replicas=1
                deployment.kubernetes.io/max-replicas=2
                deployment.kubernetes.io/revision=2
                description=Service based on rabbitmq.
Controlled By:  Deployment/mq-svc
Replicas:       1 current / 1 desired
Pods Status:    1 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
  Labels:  pod-template-hash=1652693485
           qcloud-app=mq-svc
  Containers:
   queue-mq:
    Image:      rabbitmq:management
    Port:       <none>
    Host Port:  <none>
    Limits:
      cpu:     500m
      memory:  1Gi
    Requests:
      cpu:        250m
      memory:     256Mi
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Events:
  Type    Reason            Age   From                   Message
  ----    ------            ----  ----                   -------
  Normal  SuccessfulCreate  50m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-r8n8t
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-l4zj2
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-m8tmv
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-m8tmv
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-r9wkj
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-8wzpq
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-d8gwc
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-d8gwc
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-8wzpq
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-l4zj2
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-r9wkj
  Normal  SuccessfulDelete  45m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-r8n8t

关键信息

Controlled By:  Deployment/mq-svc

这个RS被名字为mq-svc的Deployment控制，这样看，Deployment是比RS高一级别用于管理RS的组件。

在RS级别上发生的事件，均是对pod的操作，创建pod，删除pod

Events:
  Type    Reason            Age   From                   Message
  ----    ------            ----  ----                   -------
  Normal  SuccessfulCreate  50m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-r8n8t
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-l4zj2
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-m8tmv
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-m8tmv
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-r9wkj
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-8wzpq
  Normal  SuccessfulCreate  49m   replicaset-controller  Created pod: mq-svc-5b96bf78d9-d8gwc
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-d8gwc
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-8wzpq
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-l4zj2
  Normal  SuccessfulDelete  49m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-r9wkj
  Normal  SuccessfulDelete  45m   replicaset-controller  Deleted pod: mq-svc-5b96bf78d9-r8n8t

接下来，我们来看看Delpoyment

[root@VM_0_17_centos ~]# kubectl describe deploy  mq-svc
Name:                   mq-svc
Namespace:              default
CreationTimestamp:      Fri, 17 Aug 2018 17:21:13 +0800
Labels:                 qcloud-app=mq-svc
Annotations:            deployment.changecourse=Updating
                        deployment.kubernetes.io/revision=2
                        description=Service based on rabbitmq.
Selector:               qcloud-app=mq-svc
Replicas:               1 desired | 1 updated | 1 total | 1 available | 0 unavailable
StrategyType:           RollingUpdate
MinReadySeconds:        10
RollingUpdateStrategy:  0 max unavailable, 1 max surge
Pod Template:
  Labels:  qcloud-app=mq-svc
  Containers:
   queue-mq:
    Image:      rabbitmq:management
    Port:       <none>
    Host Port:  <none>
    Limits:
      cpu:     500m
      memory:  1Gi
    Requests:
      cpu:        250m
      memory:     256Mi
    Environment:  <none>
    Mounts:       <none>
  Volumes:        <none>
Conditions:
  Type           Status  Reason
  ----           ------  ------
  Progressing    True    NewReplicaSetAvailable
  Available      True    MinimumReplicasAvailable
OldReplicaSets:  <none>
NewReplicaSet:   mq-svc-5b96bf78d9 (1/1 replicas created)
Events:
  Type    Reason             Age   From                   Message
  ----    ------             ----  ----                   -------
  Normal  ScalingReplicaSet  58m   deployment-controller  Scaled up replica set mq-svc-5b96bf78d9 to 2
  Normal  ScalingReplicaSet  57m   deployment-controller  Scaled up replica set mq-svc-5b96bf78d9 to 3
  Normal  ScalingReplicaSet  57m   deployment-controller  Scaled up replica set mq-svc-5b96bf78d9 to 4
  Normal  ScalingReplicaSet  57m   deployment-controller  Scaled down replica set mq-svc-5b96bf78d9 to 3
  Normal  ScalingReplicaSet  57m   deployment-controller  Scaled up replica set mq-svc-5b96bf78d9 to 6
  Normal  ScalingReplicaSet  57m   deployment-controller  Scaled down replica set mq-svc-5b96bf78d9 to 4
  Normal  ScalingReplicaSet  56m   deployment-controller  Scaled down replica set mq-svc-5b96bf78d9 to 2
  Normal  ScalingReplicaSet  53m   deployment-controller  Scaled down replica set mq-svc-5b96bf78d9 to 1

可以看出，在deployment级别上，不再受其他组件的控制，而他的状态的转变是作为API被调用而产生的。我们看到，在deployment级别上发生的事件一般是创建服务、滚动升级一个服务，或者是操作RS伸缩Pod集群。

最后，到这里也很明白了，service其实是在这一整套基础之上提供给外部的稳定的服务。

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