kubernetes controller Daemonset
DaemonSet Controller: Concept and Principle Interpretation
DaemonSet overview
The DaemonSet controller can ensure that all nodes in the k8s cluster run an identical pod copy. When adding a node to the k8s cluster, the node will also automatically create a pod copy. When the node is removed from the cluster, these pods will also be created. are automatically deleted; deleting Daemonsets also deletes the pods they created.
How DaemonSets Work: How to Manage Pods?
The controller of the daemonset will listen to the daemonset object, pod object, and node object of kuberntes. The changes of these monitored objects will trigger the syncLoop cycle to make the kubernetes cluster evolve towards the state described by the daemonset object.
Typical application scenarios of Daemonset
Run a storage such as glusterd or ceph on each node of the cluster.
Run log collection components such as flunentd, logstash, filebeat, etc. on each node.
Run monitoring components such as Prometheus, Node Exporter, collectd, etc. on each node.
You can use daemonset to create and run.
The difference between DaemonSet and Deployment
The replica Pods deployed by the Deployment will be distributed on each Node, and each Node may run several replicas.
The difference with DaemonSets is that there is at most one replica running on each Node.
DaemonSet resource manifest file writing skills
#查看定义 Daemonset 资源需要的字段有哪些
[root@k8smaster ~]# kubectl explain ds
KIND: DaemonSet
VERSION: apps/v1
DESCRIPTION:
DaemonSet represents the configuration of a daemon set.
FIELDS:
apiVersion <string> #当前资源使用的 api 版本，跟 VERSION: apps/v1 保持一致
kind <string> #资源类型，跟 KIND: DaemonSet 保持一致
metadata <Object> #元数据，定义 DaemonSet 名字的
spec <Object> #定义容器的
status <Object> #状态信息，不能改
#查看 DaemonSet 的 spec 字段如何定义
[root@k8smaster ~]# kubectl explain ds.spec
KIND: DaemonSet
VERSION: apps/v1
RESOURCE: spec <Object>
DESCRIPTION:
The desired behavior of this daemon set. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status
DaemonSetSpec is the specification of a daemon set.
FIELDS:
minReadySeconds <integer> #当新的 pod 启动几秒种后，再 kill 掉旧的pod。
revisionHistoryLimit <integer> #历史版本
selector <Object> -required- #用于匹配 pod 的标签选择器
template <Object> -required- #定义 Pod 的模板，基于这个模板定义的所有 pod 是一样的
updateStrategy <Object> #daemonset 的升级策略
#查看 DaemonSet 的 spec.template 字段如何定义
#对于 template 而言，其内部定义的就是 pod，pod 模板是一个独立的对象
[root@k8smaster ~]# kubectl explain ds.spec.template
kubectl explain ds.spec.template KIND: DaemonSet
VERSION: apps/v1
RESOURCE: template <Object>
FIELDS:
metadata <Object>
spec<Object>
DaemonSet use case: deploying the log collection component fluentd
#master node1 node2 都下载 fluentd
#编写一个 DaemonSet 资源清单 daemonset 也是通过标签选择器来选择模板创建pod
[root@k8smaster ~]# mkdir ds
[root@k8smaster ~]# cd ds
[root@k8smaster ~]# kubectl explain ds.spec.template.spec.tolerations
#找到容忍度 Taints 因为没有定义value 下面定义容忍度也不用写值，写一个排斥等级就行了
[root@k8smaster ds]# vim daemonset.yaml
apiVersion: apps/v1
kind: DaemonSet
metadata:
labels:
k8s-app: fluentd-logging
name: fluentd-elasticsearch
namespace: kube-system
spec:
selector:
matchLabels:
name: fluentd-elasticsearch
template:
metadata:
name: fluentd
labels:
name: fluentd-elasticsearch
spec:
tolerations:
- key: node-role.kubernetes.io/master
effect: NoSchedule
containers:
- name: fluentd-elasticsearch
image: fluentd
resources:
limits:
memory: 500Mi
requests:
cpu: 100m
memory: 200Mi
volumeMounts:
- name: varlog
mountPath: /var/log
- name: varlibdockercontainers
mountPath: /var/lib/docker/containers
readOnly: true
terminationGracePeriodSeconds: 30
volumes:
- name: varlog
hostPath:
path: /var/log
- name: varlibdockercontainers
hostPath:
path: /var/lib/docker/containers
[root@k8smaster ds]# kubectl apply -f daemonset.yaml
daemonset.apps/fluentd-elasticsearch created
[root@k8smaster ds]# kubectl get ds -n kube-system
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
fluentd-elasticsearch 3 3 3 3 0 <none> 9s
kube-flannel-ds 3 3 3 3 3 <none> 18d
kube-proxy 3 3 3 3 3 kubernetes.io/os=linux 18d
[root@k8smaster ds]# kubectl get pods -n kube-system -o wide -l name=fluentd-elasticsearch
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE
fluentd-elasticsearch-n5jj7 1/1 Running 0 59s 10.244.1.4 k8snode2 <none>
fluentd-elasticsearch-qxgmc 1/1 Running 0 59s 10.244.0.2 k8smaster <none>
fluentd-elasticsearch-rhhv8 1/1 Running 0 59s 10.244.2.6 k8snode <none>
#通过上面可以看到在 k8s 的三个节点均创建了 fluentd 这个 pod
#pod 的名字是由控制器的名字-随机数组成的
#资源清单详细说明
apiVersion: apps/v1 #DaemonSet 使用的 api 版本
kind: DaemonSet # 资源类型
metadata:
name: fluentd-elasticsearch #资源的名字
namespace: kube-system #资源所在的名称空间
labels:
k8s-app: fluentd-logging #资源具有的标签
spec:
selector: #标签选择器
matchLabels:
name: fluentd-elasticsearch
template:
metadata:
labels: #基于这回模板定义的 pod 具有的标签
name: fluentd-elasticsearch
spec:
tolerations: #定义容忍度
- key: node-role.kubernetes.io/master
effect: NoSchedule #只会影响新调度的pod
containers: #定义容器
- name: fluentd-elasticsearch
image: xianchao/fluentd:v2.5.1
resources: #资源配额
limits: #最大资源
memory: 200Mi
requests: #最小资源
cpu: 100m
memory: 200Mi
volumeMounts:
- name: varlog
mountPath: /var/log #把本地/var/log 目录挂载到容器
- name: varlibdockercontainers
mountPath: /var/lib/docker/containers #把/var/lib/docker/containers/挂载到容器里
readOnly: true #挂载目录是只读权限
terminationGracePeriodSeconds: 30 #优雅的关闭服务
volumes:
- name: varlog
hostPath:
path: /var/log #基于本地目录创建一个卷 会去采集这个目录下的日志
- name: varlibdockercontainers
hostPath:
path: /var/lib/docker/containers #基于本地目录创建一个卷 同上
Daemonset manages pods: rolling updates
#DaemonSet 实现 pod 的滚动更新
#查看 daemonset 的滚动更新策略
[root@k8smaster ds]# kubectl explain ds.spec.updateStrategy
KIND: DaemonSet
VERSION: apps/v1
RESOURCE: updateStrategy <Object>
DESCRIPTION:
An update strategy to replace existing DaemonSet pods with new pods.
DaemonSetUpdateStrategy is a struct used to control the update strategy for
a DaemonSet.
FIELDS:
rollingUpdate <Object>
Rolling update config params. Present only if type = "RollingUpdate".
type <string>
Type of daemon set update. Can be "RollingUpdate" or "OnDelete". Default is
RollingUpdate.
#查看 rollingUpdate 支持的更新策略
[root@k8smaster ds]# kubectl explain ds.spec.updateStrategy.rollingUpdate
KIND: DaemonSet
VERSION: apps/v1
RESOURCE: rollingUpdate <Object>
DESCRIPTION:
Rolling update config params. Present only if type = "RollingUpdate".
Spec to control the desired behavior of daemon set rolling update.
FIELDS:
maxUnavailable <string>
#上面表示 rollingUpdate 更新策略只支持 maxUnavailabe，先删除在更新；因为我们不支持一个节点运行两个 pod，因此需要先删除一个，在更新一个。
#更新镜像版本，可以按照如下方法：
[root@k8smaster ds]# kubectl set image daemonsets fluentd-elasticsearch fluentd-elasticsearch=nginx -n kube-system
daemonset.apps/fluentd-elasticsearch image updated
#这个镜像启动 pod 会有问题，主要是演示 daemonset 如何在命令行更新 pod 平时不用 都是改yaml
[root@k8smaster ds]# kubectl set image daemonsets fluentd-elasticsearch fluentd-elasticsearch=fluentd -n kube-system
daemonset.apps/fluentd-elasticsearch image updated
#改回来
[root@k8smaster ds]# kubectl get pods -n kube-system
NAME READY STATUS RESTARTS AGE
fluentd-elasticsearch-874qw 1/1 Running 0 23s
fluentd-elasticsearch-lmvjq 1/1 Running 0 26s
fluentd-elasticsearch-qxgmc 1/1 Running 0 8m29s
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