Kubernetes 学习7 Pod控制器应用进阶2

一、容器探测器

　　1、所谓的容器探测无非就是我们在里面设置了一些探针，或者称之为传感器来获取相应的数据作为判定其存活与否或就绪与否的标准，目前k8s所支持的存活性和就绪性探测方式都是一样的。

　　2、k8s的探针类型有三种

　　　　1、ExecAction

　　　　2、TCPSocketAction：TCPSocket探针

　　　　3、HTTPGetAction ： 如果对方是http服务那么直接向对方发http的get请求就可以了

　　3、相应字段在  pods.spec.containers 之上

　　　　a、livenessProbe <Object>

[root@k8smaster ~]# kubectl explain  pods.spec.containers.livenessProbe
KIND:     Pod
VERSION:  v1

RESOURCE: livenessProbe <Object>

DESCRIPTION:
     Periodic probe of container liveness. Container will be restarted if the
     probe fails. Cannot be updated. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes

     Probe describes a health check to be performed against a container to
     determine whether it is alive or ready to receive traffic.

FIELDS:
   exec    <Object> #探针
     One and only one of the following should be specified. Exec specifies the
     action to take.

   failureThreshold    <integer> #探测几次都失败才定义失败，默认为3，最小值为1
     Minimum consecutive failures for the probe to be considered failed after
     having succeeded. Defaults to 3. Minimum value is 1.

   httpGet    <Object>
     HTTPGet specifies the http request to perform.

   initialDelaySeconds    <integer> #不可能主程序启动以后立即对其做探测，因为有可能还没有初始化完成，因此我们要稍微等一点时间再探测，因此其意思为初始化后的延迟探测时间，不定义默认为容器一启动就开始探测。
     Number of seconds after the container has started before liveness probes
     are initiated. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes

   periodSeconds    <integer> #默认每10秒钟探测一次
     How often (in seconds) to perform the probe. Default to 10 seconds. Minimum
     value is 1.

   successThreshold    <integer>
     Minimum consecutive successes for the probe to be considered successful
     after having failed. Defaults to 1. Must be 1 for liveness. Minimum value
     is 1.

   tcpSocket    <Object>
     TCPSocket specifies an action involving a TCP port. TCP hooks not yet
     supported

   timeoutSeconds    <integer> #探测超时时长，默认为1秒
     Number of seconds after which the probe times out. Defaults to 1 second.
     Minimum value is 1. More info:
     https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle#container-probes

　　　　b、readinessProbe <Object>

　　　　c、lifecycle <Object> #生命周期，定义启动后和终止前钩子的

　　4、exec指针探测

[root@k8smaster ~]# kubectl explain  pods.spec.containers.livenessProbe.exec
KIND:     Pod
VERSION:  v1

RESOURCE: exec <Object>

DESCRIPTION:
     One and only one of the following should be specified. Exec specifies the
     action to take.

     ExecAction describes a "run in container" action.

FIELDS:
   command    <[]string>  #运行命令以后来探测其是否执行成功了，如果这个命令的返回值是成功表示存活，若返回值状态码是不成功表示不存活。
     Command is the command line to execute inside the container, the working
     directory for the command is root ('/') in the container's filesystem. The
     command is simply exec'd, it is not run inside a shell, so traditional
     shell instructions ('|', etc) won't work. To use a shell, you need to
     explicitly call out to that shell. Exit status of 0 is treated as
     live/healthy and non-zero is unhealthy.

[root@k8smaster manifests]# ls
liveness-exec.yaml  pod-demo.yaml
[root@k8smaster manifests]# cat liveness-exec.yaml 
apiVersion: v1
kind: Pod
metadata: 
  name: liveness-exec-pod
  namespace: default
spec:
  containers:
  - name: liveness-exec-container
    image: busybox:latest
    imagePullPolicy: IfNotPresent
    command: ["/bin/sh","-c","touch /tmp/healthy; sleep 30; rm -f /tmp/healthy; sleep 3600"]
    livenessProbe:
      exec:
        command: ["test","-e","/tmp/healthy"] #判断此文件是否存在
      initialDelaySeconds: 1 #容器启动后等待1秒开始探测
      periodSeconds: 3 #每隔3秒探测一次
  restartPolicy: Always
[root@k8smaster manifests]# kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
liveness-exec-pod             1/1       Running   6          9m
myapp-848b5b879b-5k4s4        1/1       Running   0          4d
myapp-848b5b879b-bzblz        1/1       Running   0          4d
myapp-848b5b879b-hzbf5        1/1       Running   0          4d
nginx-deploy-5b595999-d9lv5   1/1       Running   0          4d
pod-demo                      2/2       Running   3          5h
[root@k8smaster manifests]# kubectl describe pod liveness-exec-pod 
Name:               liveness-exec-pod
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               k8snode2/192.168.10.12
Start Time:         Thu, 09 May 2019 19:59:15 +0800
Labels:             <none>
Annotations:        <none>
Status:             Running
IP:                 10.244.2.17
Containers:
  liveness-exec-container:
    Container ID:  docker://37b9faa3b66df5f74ce43943e20d414a6e0498b261b65e11e7c89ab26c633109
    Image:         busybox:latest
    Image ID:      docker-pullable://busybox@sha256:4b6ad3a68d34da29bf7c8ccb5d355ba8b4babcad1f99798204e7abb43e54ee3d
    Port:          <none>
    Host Port:     <none>
    Command:
      /bin/sh
      -c
      touch /tmp/healthy; sleep 30; rm -f /tmp/healthy; sleep 3600
    State:          Running
      Started:      Thu, 09 May 2019 20:07:42 +0800
    Last State:     Terminated
      Reason:       Error
      Exit Code:    137
      Started:      Thu, 09 May 2019 20:05:00 +0800
      Finished:     Thu, 09 May 2019 20:06:09 +0800
    Ready:          True
    Restart Count:  6
    Liveness:       exec [test -e /tmp/healthy] delay=1s timeout=1s period=3s #success=1 #failure=3
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-jvtl7 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-jvtl7:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-jvtl7
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason     Age               From               Message
  ----     ------     ----              ----               -------
  Normal   Pulled     4d (x4 over 4d)   kubelet, k8snode2  Container image "busybox:latest" already present on machine
  Normal   Created    4d (x4 over 4d)   kubelet, k8snode2  Created container
  Normal   Started    4d (x4 over 4d)   kubelet, k8snode2  Started container
  Normal   Killing    4d (x3 over 4d)   kubelet, k8snode2  Killing container with id docker://liveness-exec-container:Container failed liveness probe.. Container will be killed and recreate
d.  Warning  Unhealthy  4d (x13 over 4d)  kubelet, k8snode2  Liveness probe failed:
  Normal   Scheduled  9m                default-scheduler  Successfully assigned default/liveness-exec-pod to k8snode2

　　5、基于tcpSocket探测

[root@k8smaster manifests]#  kubectl explain  pods.spec.containers.livenessProbe.tcpSocket
KIND:     Pod
VERSION:  v1

RESOURCE: tcpSocket <Object>

DESCRIPTION:
     TCPSocket specifies an action involving a TCP port. TCP hooks not yet
     supported

     TCPSocketAction describes an action based on opening a socket

FIELDS:
   host    <string> #基于主机，默认为pod自己的IP地址
     Optional: Host name to connect to, defaults to the pod IP.

   port    <string> -required- #基于端口
     Number or name of the port to access on the container. Number must be in
     the range 1 to 65535. Name must be an IANA_SVC_NAME.

　　6、httpGet探测

[root@k8smaster manifests]#  kubectl explain  pods.spec.containers.livenessProbe.httpGet
KIND:     Pod
VERSION:  v1

RESOURCE: httpGet <Object>

DESCRIPTION:
     HTTPGet specifies the http request to perform.

     HTTPGetAction describes an action based on HTTP Get requests.

FIELDS:
   host    <string>
     Host name to connect to, defaults to the pod IP. You probably want to set
     "Host" in httpHeaders instead.

   httpHeaders    <[]Object>
     Custom headers to set in the request. HTTP allows repeated headers.

   path    <string> #指定地址指定端口的url发送请求，如果响应码为200则ok
     Path to access on the HTTP server.

   port    <string> -required- #可以直接引用service的名称而不用端口号
     Name or number of the port to access on the container. Number must be in
     the range 1 to 65535. Name must be an IANA_SVC_NAME.

   scheme    <string>
     Scheme to use for connecting to the host. Defaults to HTTP.

　　　　案例如下

[root@k8smaster manifests]# cat liveness-httpget.yaml 
apiVersion: v1
kind: Pod
metadata: 
  name: liveness-httpget-pod
  namespace: default
spec:
  containers:
  - name: liveness-httpget-container
    image: ikubernetes/myapp:v1
    imagePullPolicy: IfNotPresent
    ports:
    - name: http
      containerPort: 80
    livenessProbe:
      httpGet:
        port: http #也可以使用80
        path: /index.html
      initialDelaySeconds: 1 #容器启动后等待1秒开始探测
      periodSeconds: 3 #每隔3秒探测一次
  restartPolicy: Always

　　7、就绪性探测，其与service调度有着重要的关联性。如果不做就绪性探测那么pod刚创建就立即被关联到service后端对象中，此时pod如果未就绪将造成服务无法被访问，因此几乎只要使用pod就必须做readinessProbe（就绪性检测）。

　　　　其检测方式和探针与liveness一样，只是目标不一样，livenessProbe只是为了判断存活与否，而readinessProbe则是用来判断它就绪与否。因此只是探测命令可能会不一样。

[root@k8smaster manifests]# cat readiness-httpget.yaml 
apiVersion: v1
kind: Pod
metadata: 
  name: readiness-httpget-pod
  namespace: default
spec:
  containers:
  - name: readiness-httpget-container
    image: ikubernetes/myapp:v1
    imagePullPolicy: IfNotPresent
    ports:
    - name: http
      containerPort: 80
    readinessProbe:
      httpGet:
        port: http #也可以使用80
        path: /index.html
      initialDelaySeconds: 1 #容器启动后等待1秒开始探测
      periodSeconds: 3 #每隔3秒探测一次
  restartPolicy: Always

[root@k8smaster manifests]# kubectl create -f readiness-httpget.yaml 
pod/readiness-httpget-pod created
[root@k8smaster manifests]# kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
liveness-httpget-pod          1/1       Running   1          32m
myapp-848b5b879b-5k4s4        1/1       Running   0          4d
myapp-848b5b879b-bzblz        1/1       Running   0          4d
myapp-848b5b879b-hzbf5        1/1       Running   0          4d
nginx-deploy-5b595999-d9lv5   1/1       Running   0          5d
pod-demo                      2/2       Running   4          6h
readiness-httpget-pod         1/1       Running   0          6s
[root@k8smaster manifests]# kubectl describe pod readiness-httpget-pod
Name:               readiness-httpget-pod
Namespace:          default
Priority:           0
PriorityClassName:  <none>
Node:               k8snode2/192.168.10.12
Start Time:         Thu, 09 May 2019 21:02:50 +0800
Labels:             <none>
Annotations:        <none>
Status:             Running
IP:                 10.244.2.19
Containers:
  readiness-httpget-container:
    Container ID:   docker://2972a892e1c91c2cfa6168f5729cbf1dae02e079f5bd1e8dc370e2ed56dcbf61
    Image:          ikubernetes/myapp:v1
    Image ID:       docker-pullable://ikubernetes/myapp@sha256:9c3dc30b5219788b2b8a4b065f548b922a34479577befb54b03330999d30d513
    Port:           80/TCP
    Host Port:      0/TCP
    State:          Running
      Started:      Thu, 09 May 2019 21:02:51 +0800
    Ready:          True
    Restart Count:  0
    Readiness:      http-get http://:http/index.html delay=1s timeout=1s period=3s #success=1 #failure=3
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-jvtl7 (ro)
Conditions:
  Type              Status
  Initialized       True 
  Ready             True 
  ContainersReady   True 
  PodScheduled      True 
Volumes:
  default-token-jvtl7:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-jvtl7
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Pulled     4d    kubelet, k8snode2  Container image "ikubernetes/myapp:v1" already present on machine
  Normal  Created    4d    kubelet, k8snode2  Created container
  Normal  Started    4d    kubelet, k8snode2  Started container
  Normal  Scheduled  23s   default-scheduler  Successfully assigned default/readiness-httpget-pod to k8snode2

#进入容器删除index.html发现不再ready
[root@k8smaster manifests]# kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
liveness-httpget-pod          1/1       Running   1          34m
myapp-848b5b879b-5k4s4        1/1       Running   0          4d
myapp-848b5b879b-bzblz        1/1       Running   0          4d
myapp-848b5b879b-hzbf5        1/1       Running   0          4d
nginx-deploy-5b595999-d9lv5   1/1       Running   0          5d
pod-demo                      2/2       Running   4          6h
readiness-httpget-pod         0/1       Running   0          2m

 　　8、lifecycle <Object> #生命周期，定义启动后和终止前钩子的

[root@k8smaster manifests]# kubectl explain  pods.spec.containers.lifecycle
KIND:     Pod
VERSION:  v1

RESOURCE: lifecycle <Object>

DESCRIPTION:
     Actions that the management system should take in response to container
     lifecycle events. Cannot be updated.

     Lifecycle describes actions that the management system should take in
     response to container lifecycle events. For the PostStart and PreStop
     lifecycle handlers, management of the container blocks until the action is
     complete, unless the container process fails, in which case the handler is
     aborted.

FIELDS:
   postStart    <Object> #容器启动后立即执行的操作
     PostStart is called immediately after a container is created. If the
     handler fails, the container is terminated and restarted according to its
     restart policy. Other management of the container blocks until the hook
     completes. More info:
     https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/#container-hooks

   preStop    <Object> #容器终止前执行的操作
     PreStop is called immediately before a container is terminated. The
     container is terminated after the handler completes. The reason for
     termination is passed to the handler. Regardless of the outcome of the
     handler, the container is eventually terminated. Other management of the
     container blocks until the hook completes. More info:
     https://kubernetes.io/docs/concepts/containers/container-lifecycle-hooks/#container-hooks

　　　　a、postStart ，默认会在容器的command命令运行完后再运行其定义的命令。

[root@k8smaster manifests]# more poststart-pod.yaml 
apiVersion: v1
kind: Pod
metadata:
    name: poststart-pod
    namespace: default
spec:
    containers:
    - name: busybox-pod
      image: busybox:latest
      imagePullPolicy: IfNotPresent
      lifecycle:
        postStart:
          exec:
            command: ["mkdir","-p","/data/web/html"]
      command: ["/bin/sh","-c"] #默认此命令+args执行完才会执行上面的postStart.exec.command中的命令
      args: ["sleep 3600"]
[root@k8smaster manifests]# kubectl exec -it  poststart-pod /bin/sh
/ # ls /data/web/html/
/ # exit
[root@k8smaster manifests]# kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
liveness-httpget-pod          1/1       Running   1          1h
myapp-848b5b879b-5k4s4        1/1       Running   0          4d
myapp-848b5b879b-bzblz        1/1       Running   0          4d
myapp-848b5b879b-hzbf5        1/1       Running   0          4d
nginx-deploy-5b595999-d9lv5   1/1       Running   0          5d
pod-demo                      2/2       Running   5          7h
poststart-pod                 1/1       Running   0          1m
readiness-httpget-pod         1/1       Running   0          58m

　　　　b、preStop ，和postStart类似