k8s(Kubernetes) 中 Pod,Deployment,ReplicaSet,Service 之间关系分析
发布于: 2021 年 03 月 24 日
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 podsNAME READY STATUS RESTARTS AGEmq-svc-5b96bf78d9-brpjw 1/1 Running 0 51m复制代码
来看一下它的详情
[root@VM_0_17_centos ~]# kubectl describe pod mq-svc-5b96bf78d9-brpjwName: mq-svc-5b96bf78d9-brpjwNamespace: defaultNode: 10.0.0.17/10.0.0.17Start Time: Fri, 17 Aug 2018 17:24:44 +0800Labels: pod-template-hash=1652693485 qcloud-app=mq-svcAnnotations: <none>Status: RunningIP: 172.16.0.39Controlled By: ReplicaSet/mq-svc-5b96bf78d9Containers: 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: falseQoS Class: BurstableNode-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复制代码
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复制代码
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复制代码
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-5b96bf78d9Name: mq-svc-5b96bf78d9Namespace: defaultSelector: pod-template-hash=1652693485,qcloud-app=mq-svcLabels: pod-template-hash=1652693485 qcloud-app=mq-svcAnnotations: 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-svcReplicas: 1 current / 1 desiredPods Status: 1 Running / 0 Waiting / 0 Succeeded / 0 FailedPod 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复制代码
关键信息
Controlled By: Deployment/mq-svc复制代码
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复制代码
接下来，我们来看看 Delpoyment
[root@VM_0_17_centos ~]# kubectl describe deploy mq-svcName: mq-svcNamespace: defaultCreationTimestamp: Fri, 17 Aug 2018 17:21:13 +0800Labels: qcloud-app=mq-svcAnnotations: deployment.changecourse=Updating deployment.kubernetes.io/revision=2 description=Service based on rabbitmq.Selector: qcloud-app=mq-svcReplicas: 1 desired | 1 updated | 1 total | 1 available | 0 unavailableStrategyType: RollingUpdateMinReadySeconds: 10RollingUpdateStrategy: 0 max unavailable, 1 max surgePod 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 MinimumReplicasAvailableOldReplicaSets: <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复制代码
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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发布于: 2021 年 03 月 24 日阅读数: 11
版权声明: 本文为 InfoQ 作者【ucsheep】的原创文章。
原文链接:【http://xie.infoq.cn/article/a713bfc505fbcfddbe364a40a】。未经作者许可，禁止转载。
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