1. 健康检查

1.1 健康检查概述

应用在运行过程中难免会出现错误，如程序异常，软件异常，硬件故障，网络故障等，kubernetes提供Health Check健康检查机制，当发现应用异常时会自动重启容器，将应用从service服务中剔除，保障应用的高可用性。k8s定义了三种探针Probe：

• readiness probes 准备就绪检查，通过readiness是否准备接受流量，准备完毕加入到endpoint，否则剔除
• liveness probes 在线检查机制，检查应用是否可用，如死锁，无法响应，异常时会自动重启容器
• startup probes 启动检查机制，应用一些启动缓慢的业务，避免业务长时间启动而被前面的探针kill掉

每种探测机制支持三种健康检查方法，分别是命令行exec，httpGet和tcpSocket，其中exec通用性最强，适用与大部分场景，tcpSocket适用于TCP业务，httpGet适用于web业务。

• exec 提供命令或shell的检测，在容器中执行命令检查，返回码为0健康，非0异常
• httpGet http协议探测，在容器中发送http请求，根据http返回码判断业务健康情况
• tcpSocket tcp协议探测，向容器发送tcp建立连接，能建立则说明正常

每种探测方法能支持几个相同的检查参数，用于设置控制检查时间：

• initialDelaySeconds 初始第一次探测间隔，用于应用启动的时间，防止应用还没启动而健康检查失败
• periodSeconds 检查间隔，多久执行probe检查，默认为10s
• timeoutSeconds 检查超时时长，探测应用timeout后为失败
• successThreshold 成功探测阈值，表示探测多少次为健康正常，默认探测1次

1.2 exec命令行健康检查

许多应用程序运行过程中无法检测到内部故障，如死锁，出现故障时通过重启业务可以恢复，kubernetes提供liveness在线健康检查机制，我们以exec为例，创建一个容器启动过程中创建一个文件/tmp/liveness-probe.log，10s后将其删除，定义liveness健康检查机制在容器中执行命令ls -l /tmp/liveness-probe.log，通过文件的返回码判断健康状态，如果返回码非0，暂停20s后kubelet会自动将该容器重启。

1、定义一个容器，启动时创建一个文件，健康检查时ls -l /tmp/liveness-probe.log返回码为0，健康检查正常，10s后将其删除，返回码为非0，健康检查异常

[root@node-1 demo]# cat centos-exec-liveness-probe.yaml
apiVersion: v1
kind: Pod
metadata:
  name: exec-liveness-probe
  annotations:
    kubernetes.io/description: "exec-liveness-probe"
spec:
  containers:
  - name: exec-liveness-probe
    image: centos:latest
    imagePullPolicy: IfNotPresent
    args:    #容器启动命令，生命周期为30s
    - /bin/sh
    - -c
    - touch /tmp/liveness-probe.log && sleep 10 && rm -f /tmp/liveness-probe.log && sleep 20
    livenessProbe:
      exec:  #健康检查机制，通过ls -l /tmp/liveness-probe.log返回码判断容器的健康状态
        command:
        - ls 
        - l 
        - /tmp/liveness-probe.log
      initialDelaySeconds: 1
      periodSeconds: 5
      timeoutSeconds: 1

2、应用配置生成容器

[root@node-1 demo]# kubectl apply -f centos-exec-liveness-probe.yaml 
pod/exec-liveness-probe created

3、查看容器的event日志，容器启动后，10s以内容器状态正常，11s开始执行liveness健康检查，检查异常，触发容器重启

[root@node-1 demo]# kubectl describe pods exec-liveness-probe | tail
Events:
  Type     Reason     Age                From               Message
  ----     ------     ----               ----               -------
  Normal   Scheduled  28s                default-scheduler  Successfully assigned default/exec-liveness-probe to node-3
  Normal   Pulled     27s                kubelet, node-3    Container image "centos:latest" already present on machine
  Normal   Created    27s                kubelet, node-3    Created container exec-liveness-probe
  Normal   Started    27s                kubelet, node-3    Started container exec-liveness-probe
  #容器已启动
  Warning  Unhealthy  20s (x2 over 25s)  kubelet, node-3    Liveness probe failed: /tmp/liveness-probe.log
ls: cannot access l: No such file or directory #执行健康检查，检查异常
  Warning  Unhealthy  15s  kubelet, node-3  Liveness probe failed: ls: cannot access l: No such file or directory
ls: cannot access /tmp/liveness-probe.log: No such file or directory
  Normal  Killing  15s  kubelet, node-3  Container exec-liveness-probe failed liveness probe, will be restarted
  #重启容器

4、查看容器重启次数，容器不停的执行，重启次数会响应增加，可以看到RESTARTS的次数在持续增加

[root@node-1 demo]# kubectl get pods exec-liveness-probe 
NAME                  READY   STATUS    RESTARTS   AGE
exec-liveness-probe   1/1     Running   6          5m19s

1.3 httpGet健康检查

1、httpGet probe主要主要用于web场景，通过向容器发送http请求，根据返回码判断容器的健康状态，返回码小于4xx即表示健康，如下定义一个nginx应用，通过探测http://<container>:port/index.html的方式判断健康状态

[root@node-1 demo]# cat nginx-httpGet-liveness-readiness.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: nginx-httpget-livess-readiness-probe 
  annotations:
    kubernetes.io/description: "nginx-httpGet-livess-readiness-probe"
spec:
  containers:
  - name: nginx-httpget-livess-readiness-probe
    image: nginx:latest
    ports:
    - name: http-80-port
      protocol: TCP
      containerPort: 80
    livenessProbe:   #健康检查机制，通过httpGet实现实现检查
      httpGet:
        port: 80
        scheme: HTTP
        path: /index.html
      initialDelaySeconds: 3
      periodSeconds: 10
      timeoutSeconds: 3

2、生成pod并查看健康状态

[root@node-1 demo]# kubectl apply -f nginx-httpGet-liveness-readiness.yaml 
pod/nginx-httpget-livess-readiness-probe created
[root@node-1 demo]# kubectl get pods nginx-httpget-livess-readiness-probe 
NAME                                   READY   STATUS    RESTARTS   AGE
nginx-httpget-livess-readiness-probe   1/1     Running   0          6s

3、模拟故障，将pod中的path文件所属文件删除，此时发送http请求时会健康检查异常，会触发容器自动重启

查询pod所属的节点
[root@node-1 demo]# kubectl get pods nginx-httpget-livess-readiness-probe -o wide 
NAME                                   READY   STATUS    RESTARTS   AGE    IP            NODE     NOMINATED NODE   READINESS GATES
nginx-httpget-livess-readiness-probe   1/1     Running   1          3m9s   10.244.2.19   node-3   <none>           <none>

登录到pod中将文件删除
[root@node-1 demo]# kubectl exec -it nginx-httpget-livess-readiness-probe /bin/bash
root@nginx-httpget-livess-readiness-probe:/# ls -l /usr/share/nginx/html/index.html 
-rw-r--r-- 1 root root 612 Sep 24 14:49 /usr/share/nginx/html/index.html
root@nginx-httpget-livess-readiness-probe:/# rm -f /usr/share/nginx/html/index.html 

4、再次查看pod的列表，此时会RESTART的次数会增加1，表示重启重启过一次，AGE则多久前重启的时间

[root@node-1 demo]# kubectl get pods nginx-httpget-livess-readiness-probe 
NAME                                   READY   STATUS    RESTARTS   AGE
nginx-httpget-livess-readiness-probe   1/1     Running   1          4m22s

5、查看pod的详情，观察容器重启的情况，通过Liveness 检查容器出现404错误，触发重启。

[root@node-1 demo]# kubectl describe pods nginx-httpget-livess-readiness-probe | tail
Events:
  Type     Reason     Age                    From               Message
  ----     ------     ----                   ----               -------
  Normal   Scheduled  5m45s                  default-scheduler  Successfully assigned default/nginx-httpget-livess-readiness-probe to node-3
  Normal   Pulling    3m29s (x2 over 5m45s)  kubelet, node-3    Pulling image "nginx:latest"
  Warning  Unhealthy  3m29s (x3 over 3m49s)  kubelet, node-3    Liveness probe failed: HTTP probe failed with statuscode: 404
  Normal   Killing    3m29s                  kubelet, node-3    Container nginx-httpget-livess-readiness-probe failed liveness probe, will be restarted
  Normal   Pulled     3m25s (x2 over 5m41s)  kubelet, node-3    Successfully pulled image "nginx:latest"
  Normal   Created    3m25s (x2 over 5m40s)  kubelet, node-3    Created container nginx-httpget-livess-readiness-probe
  Normal   Started    3m25s (x2 over 5m40s)  kubelet, node-3    Started container nginx-httpget-livess-readiness-probe

1.4 tcpSocket健康检查

1、tcpsocket健康检查适用于TCP业务，通过向指定容器建立一个tcp连接，可以建立连接则健康检查正常，否则健康检查异常，依旧以nignx为例使用tcp健康检查机制，探测80端口的连通性

[root@node-1 demo]# cat nginx-tcp-liveness.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: nginx-tcp-liveness-probe
  annotations:
    kubernetes.io/description: "nginx-tcp-liveness-probe"
spec:
  containers:
  - name: nginx-tcp-liveness-probe 
    image: nginx:latest
    ports:
    - name: http-80-port
      protocol: TCP
      containerPort: 80
    livenessProbe:  #健康检查为tcpSocket，探测TCP 80端口
      tcpSocket:
       port: 80
      initialDelaySeconds: 3
      periodSeconds: 10
      timeoutSeconds: 3

2、应用配置创建容器

[root@node-1 demo]# kubectl apply -f nginx-tcp-liveness.yaml 
pod/nginx-tcp-liveness-probe created

[root@node-1 demo]# kubectl get pods nginx-tcp-liveness-probe 
NAME                       READY   STATUS    RESTARTS   AGE
nginx-tcp-liveness-probe   1/1     Running   0          6s

3、模拟故障，获取pod所属节点，登录到pod中，安装查看进程工具htop

获取pod所在node
[root@node-1 demo]# kubectl get pods nginx-tcp-liveness-probe -o wide 
NAME                       READY   STATUS    RESTARTS   AGE   IP            NODE     NOMINATED NODE   READINESS GATES
nginx-tcp-liveness-probe   1/1     Running   0          99s   10.244.2.20   node-3   <none>           <none>

登录到pod中
[root@node-1 demo]# kubectl exec -it nginx-httpget-livess-readiness-probe /bin/bash

#执行apt-get update更新和apt-get install htop安装工具
root@nginx-httpget-livess-readiness-probe:/# apt-get update      
Get:1 http://cdn-fastly.deb.debian.org/debian buster InRelease [122 kB]             
Get:2 http://security-cdn.debian.org/debian-security buster/updates InRelease [39.1 kB]     
Get:3 http://cdn-fastly.deb.debian.org/debian buster-updates InRelease [49.3 kB]            
Get:4 http://security-cdn.debian.org/debian-security buster/updates/main amd64 Packages [95.7 kB]
Get:5 http://cdn-fastly.deb.debian.org/debian buster/main amd64 Packages [7899 kB]
Get:6 http://cdn-fastly.deb.debian.org/debian buster-updates/main amd64 Packages [5792 B]
Fetched 8210 kB in 3s (3094 kB/s)
Reading package lists... Done
root@nginx-httpget-livess-readiness-probe:/# apt-get install htop
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Suggested packages:
  lsof strace
The following NEW packages will be installed:
  htop
0 upgraded, 1 newly installed, 0 to remove and 5 not upgraded.
Need to get 92.8 kB of archives.
After this operation, 230 kB of additional disk space will be used.
Get:1 http://cdn-fastly.deb.debian.org/debian buster/main amd64 htop amd64 2.2.0-1+b1 [92.8 kB]
Fetched 92.8 kB in 0s (221 kB/s)
debconf: delaying package configuration, since apt-utils is not installed
Selecting previously unselected package htop.
(Reading database ... 7203 files and directories currently installed.)
Preparing to unpack .../htop_2.2.0-1+b1_amd64.deb ...
Unpacking htop (2.2.0-1+b1) ...
Setting up htop (2.2.0-1+b1) ...

4、运行htop查看进程，容器进程通常为1，kill掉进程观察容器状态，观察RESTART次数重启次数增加

root@nginx-httpget-livess-readiness-probe:/# kill 1
root@nginx-httpget-livess-readiness-probe:/# command terminated with exit code 137

查看pod情况
[root@node-1 demo]# kubectl get pods nginx-tcp-liveness-probe 
NAME                       READY   STATUS    RESTARTS   AGE
nginx-tcp-liveness-probe   1/1     Running   1          13m

5、查看容器详情，发现容器有重启的记录

[root@node-1 demo]# kubectl describe pods nginx-tcp-liveness-probe | tail
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason     Age                From               Message
  ----    ------     ----               ----               -------
  Normal  Scheduled  14m                default-scheduler  Successfully assigned default/nginx-tcp-liveness-probe to node-3
  Normal  Pulling    44s (x2 over 14m)  kubelet, node-3    Pulling image "nginx:latest"
  Normal  Pulled     40s (x2 over 14m)  kubelet, node-3    Successfully pulled image "nginx:latest"
  Normal  Created    40s (x2 over 14m)  kubelet, node-3    Created container nginx-tcp-liveness-probe
  Normal  Started    40s (x2 over 14m)  kubelet, node-3    Started container nginx-tcp-liveness-probe

1.5 readiness健康就绪

就绪检查用于应用接入到service的场景，用于判断应用是否已经就绪完毕，即是否可以接受外部转发的流量，健康检查正常则将pod加入到service的endpoints中，健康检查异常则从service的endpoints中删除，避免影响业务的访问。

1、创建一个pod，使用httpGet的健康检查机制，定义readiness就绪检查探针检查路径/test.html

[root@node-1 demo]# cat httpget-liveness-readiness-probe.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: nginx-tcp-liveness-probe
  annotations:
    kubernetes.io/description: "nginx-tcp-liveness-probe"
  labels:  #需要定义labels，后面定义的service需要调用
    app: nginx
spec:
  containers:
  - name: nginx-tcp-liveness-probe 
    image: nginx:latest
    ports:
    - name: http-80-port
      protocol: TCP
      containerPort: 80
    livenessProbe:  #存活检查探针
      httpGet:
        port: 80
        path: /index.html
        scheme: HTTP
      initialDelaySeconds: 3
      periodSeconds: 10
      timeoutSeconds: 3
    readinessProbe:  #就绪检查探针
      httpGet:
        port: 80
        path: /test.html
        scheme: HTTP
      initialDelaySeconds: 3
      periodSeconds: 10
      timeoutSeconds: 3

2、定义一个service，将上述的pod加入到service中，注意使用上述定义的labels，app=nginx

[root@node-1 demo]# cat nginx-service.yaml
apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx
  name: nginx-service 
spec:
  ports:
  - name: http
    port: 80 
    protocol: TCP
    targetPort: 80
  selector:
    app: nginx 
  type: ClusterIP

3、生成配置

[root@node-1 demo]# kubectl apply -f httpget-liveness-readiness-probe.yaml 
pod/nginx-tcp-liveness-probe created
[root@node-1 demo]# kubectl apply -f nginx-service.yaml 
service/nginx-service created

4、此时pod状态正常，此时readiness健康检查异常

[root@node-1 ~]# kubectl get pods nginx-httpget-livess-readiness-probe 
NAME                                   READY   STATUS    RESTARTS   AGE
nginx-httpget-livess-readiness-probe   1/1     Running   2          153m

#readiness健康检查异常，404报错（最后一行）
[root@node-1 demo]# kubectl describe pods nginx-tcp-liveness-probe | tail
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason     Age                 From               Message
  ----     ------     ----                ----               -------
  Normal   Scheduled  2m6s                default-scheduler  Successfully assigned default/nginx-tcp-liveness-probe to node-3
  Normal   Pulling    2m5s                kubelet, node-3    Pulling image "nginx:latest"
  Normal   Pulled     2m1s                kubelet, node-3    Successfully pulled image "nginx:latest"
  Normal   Created    2m1s                kubelet, node-3    Created container nginx-tcp-liveness-probe
  Normal   Started    2m1s                kubelet, node-3    Started container nginx-tcp-liveness-probe
  Warning  Unhealthy  2s (x12 over 112s)  kubelet, node-3    Readiness probe failed: HTTP probe failed with statuscode: 404

5、查看services的endpoints，发现此时endpoints为空,因为readiness就绪检查异常，kubelet认为此时pod并未就绪，因此并未将其加入到endpoints中。

[root@node-1 ~]# kubectl describe services nginx-service 
Name:              nginx-service
Namespace:         default
Labels:            app=nginx
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app":"nginx"},"name":"nginx-service","namespace":"default"},"s...
Selector:          app=nginx
Type:              ClusterIP
IP:                10.110.54.40
Port:              http  80/TCP
TargetPort:        80/TCP
Endpoints:         <none> #Endpoints对象为空
Session Affinity:  None
Events:            <none>

#endpoints状态
[root@node-1 demo]# kubectl describe endpoints nginx-service 
Name:         nginx-service
Namespace:    default
Labels:       app=nginx
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2019-09-30T14:27:37Z
Subsets:
  Addresses:          <none>
  NotReadyAddresses:  10.244.2.22  #pod处于NotReady状态
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

Events:  <none>

6、进入到pod中手动创建网站文件，使readiness健康检查正常

[root@node-1 ~]# kubectl exec -it nginx-httpget-livess-readiness-probe /bin/bash
root@nginx-httpget-livess-readiness-probe:/# echo "readiness probe demo" >/usr/share/nginx/html/test.html

7、此时readiness健康检查正常，kubelet检测到pod就绪会将其加入到endpoints中

健康检查正常
[root@node-1 demo]# curl http://10.244.2.22/test.html

查看endpoints情况
readines[root@node-1 demo]# kubectl describe endpoints nginx-service 
Name:         nginx-service
Namespace:    default
Labels:       app=nginx
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2019-09-30T14:33:01Z
Subsets:
  Addresses:          10.244.2.22 #就绪地址，已从NotReady中提出，加入到正常的Address列表中
  NotReadyAddresses:  <none>
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

查看service状态
[root@node-1 demo]# kubectl describe services nginx-service 
Name:              nginx-service
Namespace:         default
Labels:            app=nginx
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app":"nginx"},"name":"nginx-service","namespace":"default"},"s...
Selector:          app=nginx
Type:              ClusterIP
IP:                10.110.54.40
Port:              http  80/TCP
TargetPort:        80/TCP
Endpoints:         10.244.2.22:80 #已和endpoints关联
Session Affinity:  None
Events:            <none>

8、同理，如果此时容器的健康检查异常，kubelet会自动将其动endpoint中

删除站点信息，使健康检查异常
[root@node-1 demo]# kubectl exec -it nginx-tcp-liveness-probe  /bin/bash
root@nginx-tcp-liveness-probe:/# rm -f /usr/share/nginx/html/test.html 

查看pod健康检查event日志
[root@node-1 demo]# kubectl get pods nginx-tcp-liveness-probe 
NAME                       READY   STATUS    RESTARTS   AGE
nginx-tcp-liveness-probe   0/1     Running   0          11m
[root@node-1 demo]# kubectl describe pods nginx-tcp-liveness-probe | tail
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type     Reason     Age                  From               Message
  ----     ------     ----                 ----               -------
  Normal   Scheduled  12m                  default-scheduler  Successfully assigned default/nginx-tcp-liveness-probe to node-3
  Normal   Pulling    12m                  kubelet, node-3    Pulling image "nginx:latest"
  Normal   Pulled     11m                  kubelet, node-3    Successfully pulled image "nginx:latest"
  Normal   Created    11m                  kubelet, node-3    Created container nginx-tcp-liveness-probe
  Normal   Started    11m                  kubelet, node-3    Started container nginx-tcp-liveness-probe
  Warning  Unhealthy  119s (x32 over 11m)  kubelet, node-3    Readiness probe failed: HTTP probe failed with statuscode: 404

查看endpoints
[root@node-1 demo]# kubectl describe endpoints nginx-service 
Name:         nginx-service
Namespace:    default
Labels:       app=nginx
Annotations:  endpoints.kubernetes.io/last-change-trigger-time: 2019-09-30T14:38:01Z
Subsets:
  Addresses:          <none>
  NotReadyAddresses:  10.244.2.22 #健康检查异常，此时加入到NotReady状态
  Ports:
    Name  Port  Protocol
    ----  ----  --------
    http  80    TCP

Events:  <none>

查看service状态，此时endpoints为空
[root@node-1 demo]# kubectl describe services nginx-service 
Name:              nginx-service
Namespace:         default
Labels:            app=nginx
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"labels":{"app":"nginx"},"name":"nginx-service","namespace":"default"},"s...
Selector:          app=nginx
Type:              ClusterIP
IP:                10.110.54.40
Port:              http  80/TCP
TargetPort:        80/TCP
Endpoints:         #为空
Session Affinity:  None
Events:            <none>

写在最后

本章介绍kubernetes中健康检查两种Probe：livenessProbe和readinessProbe，livenessProbe主要用于存活检查，检查容器内部运行状态，readiness主要用于就绪检查，是否可以接受流量，通常需要和service的endpoints结合，当就绪准备妥当时加入到endpoints中，当就绪异常时从endpoints中删除，从而实现了services的健康检查和服务探测机制。对于Probe机制提供了三种检测的方法，分别适用于不同的场景：1. exec命令行，通过命令或shell实现健康检查，2. tcpSocket通过TCP协议探测端口，建立tcp连接，3. httpGet通过建立http请求探测，读者可多实操掌握其用法。

附录

健康检查：https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/

TKE健康检查设置方法：https://cloud.tencent.com/document/product/457/32815