1.什么是DaemonSet？
1.1DaemonSet是Pod控制器的又一种实现方式，用于在集群中的全部节点上同时运行一份指定的Pod资源副本，后续加入集群的节点也会自动创建一个相关的Pod对象，当从集群移除节点时，此类Pod对象也将被自动回收无需创建。管理员也可以使用"节点选择器"以及标签指定仅在部分具有特定特征的节点上运行指定的Pod对象。
1.2官方文档: https://kubernetes.io/zh-cn/docs/concepts/workloads/controllers/daemonset/
2.DaemonSet的用法
- 在每个节点上运行集群存储守护进程，如glusterd或Ceph；
- 在每个节点上运行日志收集守护进程，如fluentd、logstash；
- 在每个节点上运行监控系统代理程序，如Prometheus Node Exporter；
- 在每个节点上运行网络插件为Pod提供网络服务，如flannel、Calico；
- 在每个节点上运行kube-Proxy通过API-Server持续监控各个Service及其关联的Pod对象，并将其创建或变动实时反应至当前节点相应的iptables、ipvs规则上；
3.DaemonSet资源规范
DaemonSet是标准的K8s资源类型，它在Spec字段中嵌套了Selector、Template和minReadySeconds，并且功能和用法基本相同，但它不支持使用Replicas，DaemonSet并不是基于期望的副本数来控制Pod资源数量，而是基于节点数量来控制Pod数量；
apiVersion: apps/v1 # API群组及版本； kind: DaemonSet # 资源类型； metadata: # Pod元数据； name: # 资源名称，在作用域中要唯一； namespace: <string> # 名称空间，DaemonSet隶属名称空间级别； spec: minReadySeconds: <integer> # Pod就绪后多少秒内任一容器无Crash方可为就绪，来控制滚动更新的速度，默认值为0，表示新建的Pod对象一旦"就绪"将立即被视作可用，随后开始下一轮更新。如果设定了spec.minReadySeconds: 3表示新建的Pod对象至少要成功运行多久才会被视作可用，即就绪之后还要等待指定的3s才能开始下一批次的更新，在一个批次内新建的所有Pod就绪探测失败，都会导致滚动更新被终止，因此为minReadySeconds设定一个合理的值，不仅能够减缓更新的速度，还能够让Deployment提前发现一部分程序因为Bug导致的升级故障，生产环境中为Pod设置指针探测。 selector: <Object> # 标签选择器，必须匹配template字段中Pod模板中的标签； template: <Object> # Pod模板对象； metadata: <Object> # Pod名称 spec: <Object> # Pod详情 revisionHistoryLimit: <integer> # 滚动更新历史记录数量，默认为10； updateStrategy: <Object> # 滚动更新策略； type: <string> # 滚动更新类型，可用值有OnDelete和Rollingupdate； rollingUpdate: <Object> # 滚动更新参数，专用于RollingUpdate类型； maxSurge: <string> # 更新期间可比期望的Pod数量多出的数量和比例； maxUnavailable: <string> # 更新期间可比期望的Pod数量缺少的数量或比例； 4.DaemonSet部署Node_exporter示例
- Github地址:https://github.com/prometheus/node_exporter
- DockerHub地址:https://hub.docker.com/r/prom/node-exporter
- Kubernetes1.8版本起，DaemonSet也必须使用selector来匹配Pod模板中指定的标签，而且它也支持matchLabels和matchExpressions两种标签选择器；
# 示例配置文件 root@kubernetes-master01:~# cat daemonSet-node_exporter.yaml apiVersion: apps/v1 kind: DaemonSet metadata: name: node-exporter namespace: default spec: selector: matchLabels: app: node-exporter template: metadata: labels: app: node-exporter spec: hostNetwork: true # 共享主机网络 hostPID: true # 获取主机的PID containers: - name: prometheus-node-exporter image: prom/node-exporter:v0.18.0 ports: - name: node-ex-http containerPort: 9100 hostPort: 9100 # 监听在节点的9100端口上面，节点的9100，实际就在访问这个Pod livenessProbe: tcpSocket: port: node-ex-http initialDelaySeconds: 5 readinessProbe: httpGet: path: '/metrics' port: node-ex-http initialDelaySeconds: 5 root@kubernetes-master01:~# kubectl apply -f daemonSet-node_exporter.yaml 4.1 查看Pod实例；
root@kubernetes-master01:~# kubectl get pods -o wide -l app=node-exporter NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES node-exporter-l7lfh 1/1 Running 0 55s xx.0.0.xx kubernetes-xxx <none> <none> node-exporter-qljd6 1/1 Running 0 55s xx.0.0.xx kubernetes-xxx <none> <none> 4.2 describe命令查看详细信息；
# DaemonSet也可以简写为ds； root@kubernetes-master01:~# kubectl get daemonset NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE node-exporter 2 2 2 2 2 <none> 3m9s # describe查看详细信息； root@kubernetes-master01:~# kubectl describe ds node-exporter Name: node-exporter Selector: app=node-exporter Node-Selector: <none> Labels: <none> Annotations: deprecated.daemonset.template.generation: 1 Desired Number of Nodes Scheduled: 2 # 期望的Pod副本数 Current Number of Nodes Scheduled: 2 # Number of Nodes Scheduled with Up-to-date Pods: 2 Number of Nodes Scheduled with Available Pods: 2 Number of Nodes Misscheduled: 0 Pods Status: 2 Running / 0 Waiting / 0 Succeeded / 0 Failed Pod Template: # 两个Pod都是Running Labels: app=node-exporter Containers: prometheus-node-exporter: Image: prom/node-exporter:v0.18.0 # Pod使用的镜像 Port: 9100/TCP # Pod的端口 Host Port: 9100/TCP # 开启了共享宿主机端口 Liveness: tcp-socket :node-ex-http delay=5s timeout=1s period=10s #success=1 #failure=3 # 探针检测 Readiness: http-get http://:node-ex-http/metrics delay=5s timeout=1s period=10s #success=1 #failure=3 # 探针检测 Environment: <none> Mounts: <none> Volumes: <none> Events: # 调度给两个节点 Type Reason Age From Message ---- ------ ---- ---- ------- Normal SuccessfulCreate 4m26s daemonset-controller Created pod: node-exporter-qljd6 Normal SuccessfulCreate 4m26s daemonset-controller Created pod: node-exporter-l7lfh 4.3 node_exporter默认监听在TCP的9100端口，可以向任意一节点发起请求也是没有问题；
root@kubernetes-master01:~# curl -s xx.0.0.xx:9100/metrics | grep memory # HELP node_memory_Active_anon_bytes Memory information field Active_anon_bytes. # TYPE node_memory_Active_anon_bytes gauge node_memory_Active_anon_bytes 3.01551616e+08 # HELP node_memory_Active_bytes Memory information field Active_bytes. # TYPE node_memory_Active_bytes gauge node_memory_Active_bytes 8.14239744e+08 # HELP node_memory_Active_file_bytes Memory information field Active_file_bytes. # TYPE node_memory_Active_file_bytes gauge node_memory_Active_file_bytes 5.12688128e+08 # HELP node_memory_AnonHugePages_bytes Memory information field AnonHugePages_bytes. # TYPE node_memory_AnonHugePages_bytes gauge node_memory_AnonHugePages_bytes 0 5.DaemonSet更新方式
1.DaemonSet自1.16版本开始也支持滚动更新机制，相关配置定义在spec.update-Strategy嵌套字段中。目前它支持RollingUpdate(滚动更新)和OnDelete(删除式更新)两种更新策略。滚动更新为默认的更新策略。工作逻辑类似于Deployment控制，不过仅支持使用maxUnavailable属性定义最大不可用Pod资源的副本数(默认为1)而删除式更新的方式则是在删除相应节点的Pod资源后重建并更新为新版本；
5.1 RollingUpdate更新示例:
# image: prom/node-exporter:v0.18.0修改为0.18.1 root@kubernetes-master01:~# cat daemonset-node_exporter.yaml apiVersion: apps/v1 kind: DaemonSet metadata: name: node-exporter namespace: default spec: minReadySeconds: 3 revisionHistoryLimit: 20 updateStrategy: type: RollingUpdate # 更新策略 rollingUpdate: maxUnavailable: 1 selector: matchLabels: app: node-exporter template: metadata: labels: app: node-exporter spec: hostNetwork: true # 共享主机网络 hostPID: true # 获取主机的PID containers: - name: prometheus-node-exporter image: prom/node-exporter:v0.18.1 ports: - name: node-ex-http containerPort: 9100 hostPort: 9100 # 监听在节点的9100端口上面，节点的9100，实际就在访问这个Pod livenessProbe: tcpSocket: port: node-ex-http initialDelaySeconds: 5 readinessProbe: httpGet: path: '/metrics' port: node-ex-http initialDelaySeconds: 5 5.1.1执行滚动更新及状态；
root@kubernetes-master01:~# kubectl apply -f daemonset-node_exporter.yaml && kubectl rollout status daemonset node-exporter daemonset.apps/node-exporter configured Waiting for daemon set "node-exporter" rollout to finish: 0 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 0 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 0 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 1 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 1 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 1 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 1 out of 2 new pods have been updated... Waiting for daemon set "node-exporter" rollout to finish: 1 of 2 updated pods are available... Waiting for daemon set "node-exporter" rollout to finish: 1 of 2 updated pods are available... daemon set "node-exporter" successfully rolled out 5.1.2默认的RollingUpdate策略将采用一次更新一个Pod对象，待新建的Pod对象就绪后，再更新下一个Pod对象，直到全部完成。可以看到镜像版本为v0.18.1
root@kubernetes-master01:~# kubectl describe daemonsets.apps node-exporter Pod Template: Labels: app=node-exporter Containers: prometheus-node-exporter: Image: prom/node-exporter:v0.18.1 # 镜像版本已经为0.18.1 Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal SuccessfulCreate 46m daemonset-controller Created pod: node-exporter-qljd6 Normal SuccessfulCreate 46m daemonset-controller Created pod: node-exporter-l7lfh Normal SuccessfulDelete 2m34s daemonset-controller Deleted pod: node-exporter-qljd6 Normal SuccessfulCreate 2m32s daemonset-controller Created pod: node-exporter-q479h Normal SuccessfulDelete 2m21s daemonset-controller Deleted pod: node-exporter-l7lfh Normal SuccessfulCreate 2m11s daemonset-controller Created pod: node-exporter-8c2mr 5.2 OnDelete更新示例:
# 修改镜像版本为latest root@kubernetes-master01:~# cat daemonset-node_exporter.yaml apiVersion: apps/v1 kind: DaemonSet metadata: name: node-exporter namespace: default spec: minReadySeconds: 3 revisionHistoryLimit: 10 updateStrategy: # 滚动更新策略 type: OnDelete # 使用OnDelete rollingUpdate: maxUnavailable: 1 selector: matchLabels: app: node-exporter template: metadata: labels: app: node-exporter spec: hostNetwork: true # 共享主机网络 hostPID: true # 获取主机的PID containers: - name: prometheus-node-exporter image: prom/node-exporter:latest # 修改镜像版本为latest。 ports: - name: node-ex-http containerPort: 9100 hostPort: 9100 # 监听在节点的9100端口上面，节点的9100，实际就在访问这个Pod livenessProbe: tcpSocket: port: node-ex-http initialDelaySeconds: 5 readinessProbe: httpGet: path: '/metrics' port: node-ex-http initialDelaySeconds: 5 5.2.1 由于OnDelete并非自动完成升级，它需要管理员手动去删除Pod，然后重新拉起新的Pod，才能完成更新。(对于升级有着先后顺序的软件，这种方法非常有用；)
5.2.2删除Pod；
root@kubernetes-master01:~# kubectl delete pods node-exporter-8c2mr pod "node-exporter-8c2mr" deleted root@kubernetes-master01:~# kubectl delete pods node-exporter-q479h pod "node-exporter-q479h" deleted 5.2.3查看Pod已经被拉起；
root@kubernetes-master01:~# kubectl get pods -l app=node-exporter NAME READY STATUS RESTARTS AGE node-exporter-fbmkv 1/1 Running 0 99s node-exporter-hv69b 1/1 Running 0 85s 5.2.4查看Events和版本，已经升级为latest；
root@kubernetes-master01:~# kubectl describe ds node-exporter Name: node-exporter Selector: app=node-exporter Node-Selector: <none> Labels: <none> Annotations: deprecated.daemonset.template.generation: 3 Desired Number of Nodes Scheduled: 2 Current Number of Nodes Scheduled: 2 Number of Nodes Scheduled with Up-to-date Pods: 2 Number of Nodes Scheduled with Available Pods: 2 Number of Nodes Misscheduled: 0 Pods Status: 2 Running / 0 Waiting / 0 Succeeded / 0 Failed Pod Template: Labels: app=node-exporter Containers: prometheus-node-exporter: Image: prom/node-exporter:latest Port: 9100/TCP Host Port: 9100/TCP Liveness: tcp-socket :node-ex-http delay=5s timeout=1s period=10s #success=1 #failure=3 Readiness: http-get http://:node-ex-http/metrics delay=5s timeout=1s period=10s #success=1 #failure=3 Environment: <none> Mounts: <none> Volumes: <none> Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal SuccessfulCreate 3m31s daemonset-controller Created pod: node-exporter-fbmkv Normal SuccessfulCreate 3m17s daemonset-controller Created pod: node-exporter-hv69b root@kubernetes-master01:~# kubectl get pods node-exporter-fbmkv -o yaml - containerID: docker://03e895265b19f82b3086c3bd7c013f7fa5edea96551a669aac164b92ea2e26b5 image: prom/node-exporter:latest 
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