应用编排与管理 -- DaemonSet

作用

  1. 保证集群内每一个或者一些节点都运行一组相同的 Pod
  2. 跟踪集群节点状态,保证新加入的节点自动创建对应的 Pod
  3. 跟踪集群节点状态,保证移除的节点删除对应的 Pod
  4. 跟踪 Pod 状态,保证每个节点 Pod 处于运行状态

实践

YAML 文件

ds.yaml
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apiVersion: apps/v1
kind: DaemonSet
metadata:
name: fluentd-elasticsearch
namespace: kube-system
labels:
k8s-app: fluentd-logging
spec:
selector:
matchLabels:
name: fluentd-elasticsearch
template: # Pod Template
metadata:
labels:
name: fluentd-elasticsearch
spec:
containers:
- name: fluentd-elasticsearch
image: 'fluent/fluentd:v1.4-1'

查看 Node

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$ kubectl get nodes
NAME STATUS ROLES AGE VERSION
minikube Ready master 10h v1.15.5

查看 DaemonSet

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$ kubectl apply -f ds.yaml
daemonset.apps/fluentd-elasticsearch created

$ kubectl get ds -n kube-system
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
fluentd-elasticsearch 1 1 1 1 1 <none> 3m58s
kube-proxy 1 1 1 1 1 beta.kubernetes.io/os=linux 10h

$ kubectl get ds -n kube-system fluentd-elasticsearch -o yaml | head -n 15
apiVersion: extensions/v1beta1
kind: DaemonSet
metadata:
annotations:
kubectl.kubernetes.io/last-applied-configuration: |
{"apiVersion":"apps/v1","kind":"DaemonSet","metadata":{"annotations":{},"labels":{"k8s-app":"fluentd-logging"},"name":"fluentd-elasticsearch","namespace":"kube-system"},"spec":{"selector":{"matchLabels":{"name":"fluentd-elasticsearch"}},"template":{"metadata":{"labels":{"name":"fluentd-elasticsearch"}},"spec":{"containers":[{"image":"fluent/fluentd:v1.4-1","name":"fluentd-elasticsearch"}]}}}}
creationTimestamp: "2021-07-12T02:51:12Z"
generation: 1
labels:
k8s-app: fluentd-logging
name: fluentd-elasticsearch
namespace: kube-system
resourceVersion: "8703"
selfLink: /apis/extensions/v1beta1/namespaces/kube-system/daemonsets/fluentd-elasticsearch
uid: 4b3c030f-8f45-4f74-87c6-1c21899ebc31
Key Value
DESIRED 需要的 Pod 个数
CURRENT 当前已存在的 Pod 数
READY 就绪的 Pod 数
UP-TO-DATE 到达预期版本的 Pod 数
AVAILABLE 可用的 Pod 数
NODE SELECTOR 节点选择标签(筛选部分节点)

查看 Pod

Pod 的 OwnerReference 为 DaemonSet

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$ kubectl get pods -n kube-system
NAME READY STATUS RESTARTS AGE
coredns-6967fb4995-n2pk4 1/1 Running 2 10h
etcd-minikube 1/1 Running 1 10h
fluentd-elasticsearch-z4b9x 1/1 Running 0 4m25s
kube-apiserver-minikube 1/1 Running 1 10h
kube-controller-manager-minikube 1/1 Running 1 10h
kube-proxy-tjgc7 1/1 Running 1 10h
kube-scheduler-minikube 1/1 Running 1 10h
storage-provisioner 1/1 Running 2 10h

$ kubectl get pods -n kube-system fluentd-elasticsearch-z4b9x -o yaml | head -n 21
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: "2021-07-12T02:51:12Z"
generateName: fluentd-elasticsearch-
labels:
controller-revision-hash: 5fd669cccc
name: fluentd-elasticsearch
pod-template-generation: "1"
name: fluentd-elasticsearch-z4b9x
namespace: kube-system
ownerReferences:
- apiVersion: apps/v1
blockOwnerDeletion: true
controller: true
kind: DaemonSet
name: fluentd-elasticsearch
uid: 4b3c030f-8f45-4f74-87c6-1c21899ebc31
resourceVersion: "8702"
selfLink: /api/v1/namespaces/kube-system/pods/fluentd-elasticsearch-z4b9x
uid: b2b3ed75-31f9-43f5-b247-92fcb7894741

更新 DaemonSet

  1. RollingUpdate(默认):当 DaemonSet 模板更新后,老 Pod 会先被删除,然后再去创建新的 Pod,配合健康检查做滚动更新
  2. OnDelete:当 DaemonSet 模板更新后,只有手动删除某个对应的 Pod,此节点 Pod 才会被更新
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$ kubectl set image ds/fluentd-elasticsearch fluentd-elasticsearch=fluent/fluentd:v1.4 -n kube-system
daemonset.extensions/fluentd-elasticsearch image updated

$ kubectl describe ds -n kube-system fluentd-elasticsearch
Name: fluentd-elasticsearch
Selector: name=fluentd-elasticsearch
Node-Selector: <none>
Labels: k8s-app=fluentd-logging
Annotations: deprecated.daemonset.template.generation: 2
kubectl.kubernetes.io/last-applied-configuration:
{"apiVersion":"apps/v1","kind":"DaemonSet","metadata":{"annotations":{},"labels":{"k8s-app":"fluentd-logging"},"name":"fluentd-elasticsear...
Desired Number of Nodes Scheduled: 1
Current Number of Nodes Scheduled: 1
Number of Nodes Scheduled with Up-to-date Pods: 1
Number of Nodes Scheduled with Available Pods: 1
Number of Nodes Misscheduled: 0
Pods Status: 1 Running / 0 Waiting / 0 Succeeded / 0 Failed
Pod Template:
Labels: name=fluentd-elasticsearch
Containers:
fluentd-elasticsearch:
Image: fluent/fluentd:v1.4
Port: <none>
Host Port: <none>
Environment: <none>
Mounts: <none>
Volumes: <none>
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal SuccessfulCreate 24m daemonset-controller Created pod: fluentd-elasticsearch-z4b9x
Normal SuccessfulDelete 2m24s daemonset-controller Deleted pod: fluentd-elasticsearch-z4b9x
Normal SuccessfulCreate 2m12s daemonset-controller Created pod: fluentd-elasticsearch-dwmdt

$ kubectl get pods -n kube-system fluentd-elasticsearch-dwmdt -o yaml | head -n 21
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: "2021-07-12T03:13:27Z"
generateName: fluentd-elasticsearch-
labels:
controller-revision-hash: f86bfc847
name: fluentd-elasticsearch
pod-template-generation: "2"
name: fluentd-elasticsearch-dwmdt
namespace: kube-system
ownerReferences:
- apiVersion: apps/v1
blockOwnerDeletion: true
controller: true
kind: DaemonSet
name: fluentd-elasticsearch
uid: 4b3c030f-8f45-4f74-87c6-1c21899ebc31
resourceVersion: "9692"
selfLink: /api/v1/namespaces/kube-system/pods/fluentd-elasticsearch-dwmdt
uid: 8ea753ea-2ed3-4d8a-b950-c31ec6847ecd

架构设计

管理模式

纠正:跟踪 Pod 状态,而非跟踪 Job 状态

image-20210712111948819

DaemonSet Controller

  1. 纠正:不是 Job Controller,而是 DaemonSet Controller
  2. DaemonSet Controller 需要 Watch 节点状态(通过 API Server 传递到 Etcd)
  3. 当节点状态发生变化时,会通过一个内存 MQ 传递消息,DaemonSet Controller 会 Watch 到这一状态
  4. DaemonSet Controller 会查看各个节点上是否都有对应的 Pod,没有则创建,有则对比版本

image-20210712112415859

参考资料

  1. CNCF × Alibaba 云原生技术公开课
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