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# 一、容器探针简介
## 1.1 容器探测简介
容器探测用于检测容器中的应用实例是否正常工作，是保障业务可用性的一种传统机制，如果经过探测，实例的状态不符合预期，那么kubernetes就会把该问题实例“摘除”，不承担业务流量，kubernetes提供了两种探针来实现容器探测，分别是：
* livenessProbe：存活性探针，用于检测应用那个实例当前是否处于正常的运行状态，如果不是，k8s会重启容器
* readnessProbe：就绪性探针，用于检测应用实例当前是否可以接收请求，如果不能，k8s不会转发流量

即livenessProbe决定是否重启容器，readnessProb决定是否将请求转发给容器
## 1.2 容器探测方式
* exec命令：在容器内执行一次命令，如果命令执行的退出码为0，则认为程序正常，否则不正常

```yaml
  livenessProb:
    exec:
      command:
      - cat
      - /var/lib/redis.conf
```

* tcpSocket: 将会尝试访问容器一个用户容器的端口，如果能够简建立这条连接，则认为程序正常，否则不正常

```yaml
  livenessProbe:
    tcpSocket:
      port: 8000
```

* httpGet: 调用容器内web应用的url，如果返回的状态码在200-399之间，则认为程序正常，否则不正常
如下，为访问 http://192.168.2.150:80/users

```yaml
  livenessProbe:
    httpGet:
      path: /users
      port: 80
      host: 192.168.2.150
      scheme: HTTP  # 或者HTTPS
```

# 二、容器探测方式实例演示
## 2.1 exec探测方式
编辑pod_liveness_exec.yaml文件，内容如下，探测内容为查看一个不存在的文件的内容

```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev

---

apiVersion: v1
kind: Pod
metadata:
  name: pod-nginx
  namespace: dev
  labels:
    user: redrose2100
spec:
  containers:
  - name: nginx
    image: nginx:1.17.1
    livenessProbe:
      exec:
        command: ["/bin/cat","/opt/demo100.txt"]
```

使用如下命令创建

```bash
[root@master pod]# kubectl apply -f pod_liveness_exec.yaml
namespace/dev created
pod/pod-nginx created
[root@master pod]#
```
通过如下命令可以看到，此时因为探测命令失败，所以会不断地尝试去重启Pod

```bash
[root@master pod]# kubectl describe pod pod-nginx -n dev
Name:         pod-nginx
Namespace:    dev
Priority:     0
Node:         node2/192.168.16.42
Start Time:   Wed, 23 Mar 2022 00:38:37 +0800
Labels:       user=redrose2100
Annotations:  <none>
Status:       Running
IP:           10.244.2.39
IPs:
  IP:  10.244.2.39
Containers:
  nginx:
    Container ID:   docker://8ab6ad7cf41c11f903cf6beb3a0c4f9f2ff4a9d5255a64091ab1923a89a5739e
    Image:          nginx:1.17.1
    Image ID:       docker-pullable://nginx@sha256:b4b9b3eee194703fc2fa8afa5b7510c77ae70cfba567af1376a573a967c03dbb
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Wed, 23 Mar 2022 00:40:07 +0800
    Last State:     Terminated
      Reason:       Completed
      Exit Code:    0
      Started:      Wed, 23 Mar 2022 00:39:37 +0800
      Finished:     Wed, 23 Mar 2022 00:40:07 +0800
    Ready:          True
    Restart Count:  3
    Liveness:       exec [/bin/cat /opt/demo100.txt] delay=0s timeout=1s period=10s #success=1 #failure=3
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-pj5nh (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  kube-api-access-pj5nh:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type     Reason     Age                 From               Message
  ----     ------     ----                ----               -------
  Normal   Scheduled  101s                default-scheduler  Successfully assigned dev/pod-nginx to node2
  Normal   Pulled     11s (x4 over 101s)  kubelet            Container image "nginx:1.17.1" already present on machine
  Normal   Created    11s (x4 over 101s)  kubelet            Created container nginx
  Normal   Started    11s (x4 over 101s)  kubelet            Started container nginx
  Normal   Killing    11s (x3 over 71s)   kubelet            Container nginx failed liveness probe, will be restarted
  Warning  Unhealthy  1s (x10 over 91s)   kubelet            Liveness probe failed: /bin/cat: /opt/demo100.txt: No such file or directory
[root@master pod]#
```
使用如下命令删除资源
```bash
[root@master pod]# kubectl delete -f pod_liveness_exec.yaml
namespace "dev" deleted
pod "pod-nginx" deleted
[root@master pod]#
```
## 2.2 tcpSocket探测方式
编辑pod_liveness_socket.yaml文件，内容如下，使用TCPSocket的方式进行探测
```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev

---

apiVersion: v1
kind: Pod
metadata:
  name: pod-nginx
  namespace: dev
  labels:
    user: redrose2100
spec:
  containers:
  - name: nginx
    image: nginx:1.17.2
    livenessProbe:
      tcpSocket:
        port: 80

```
使用如下命令创建资源
```bash
[root@master pod]# kubectl apply -f pod_liveness_socket.yaml
namespace/dev unchanged
pod/pod-nginx created
[root@master pod]#
```
如下命令，可以发现此时探测成功
```bash
[root@master pod]# kubectl get pod -n dev
NAME        READY   STATUS    RESTARTS   AGE
pod-nginx   1/1     Running   0          74s
[root@master pod]# kubectl describe pod pod-nginx -n dev
Name:         pod-nginx
Namespace:    dev
Priority:     0
Node:         node2/192.168.16.42
Start Time:   Wed, 23 Mar 2022 00:48:54 +0800
Labels:       user=redrose2100
Annotations:  <none>
Status:       Running
IP:           10.244.2.40
IPs:
  IP:  10.244.2.40
Containers:
  nginx:
    Container ID:   docker://7383958c1f8d59cf1506ee447d7f4953d432a6c284f02df60e0c3bc0a49986a1
    Image:          nginx:1.17.2
    Image ID:       docker-pullable://nginx@sha256:5411d8897c3da841a1f45f895b43ad4526eb62d3393c3287124a56be49962d41
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Wed, 23 Mar 2022 00:49:15 +0800
    Ready:          True
    Restart Count:  0
    Liveness:       tcp-socket :80 delay=0s timeout=1s period=10s #success=1 #failure=3
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-mmq59 (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  kube-api-access-mmq59:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  84s   default-scheduler  Successfully assigned dev/pod-nginx to node2
  Normal  Pulling    84s   kubelet            Pulling image "nginx:1.17.2"
  Normal  Pulled     64s   kubelet            Successfully pulled image "nginx:1.17.2" in 20.160656657s
  Normal  Created    63s   kubelet            Created container nginx
  Normal  Started    63s   kubelet            Started container nginx
[root@master pod]#
```
使用如下命令删除资源
```bash
[root@master pod]# kubectl delete -f pod_liveness_socket.yaml
namespace "dev" deleted
pod "pod-nginx" deleted
[root@master pod]#
```
## 2.3 Http探测方式
编辑pod_liveness_http.yaml文件，内容如下：
```yaml
apiVersion: v1
kind: Namespace
metadata:
  name: dev

---

apiVersion: v1
kind: Pod
metadata:
  name: pod-nginx
  namespace: dev
  labels:
    user: redrose2100
spec:
  containers:
  - name: nginx
    image: nginx:1.17.1
    livenessProbe:
      httpGet:
        scheme: HTTP
        port: 80
        path: /
```
使用如下命令创建资源
```bash
[root@master pod]# kubectl apply -f pod_liveness_http.yaml
namespace/dev created
pod/pod-nginx created
[root@master pod]#
```
使用如下命令查询，因为nginx默认启动的是80端口，因此这里探测会成功的
```bash
[root@master pod]# kubectl get pod -n dev
NAME        READY   STATUS    RESTARTS   AGE
pod-nginx   1/1     Running   0          90s
[root@master pod]# kubectl describe pod pod-nginx -n dev
Name:         pod-nginx
Namespace:    dev
Priority:     0
Node:         node2/192.168.16.42
Start Time:   Wed, 23 Mar 2022 00:58:05 +0800
Labels:       user=redrose2100
Annotations:  <none>
Status:       Running
IP:           10.244.2.41
IPs:
  IP:  10.244.2.41
Containers:
  nginx:
    Container ID:   docker://9d0fb6c6770bb6712f94a1685cf3a763135161180bdf685124b2e0020ac046db
    Image:          nginx:1.17.1
    Image ID:       docker-pullable://nginx@sha256:b4b9b3eee194703fc2fa8afa5b7510c77ae70cfba567af1376a573a967c03dbb
    Port:           <none>
    Host Port:      <none>
    State:          Running
      Started:      Wed, 23 Mar 2022 00:58:06 +0800
    Ready:          True
    Restart Count:  0
    Liveness:       http-get http://:80/ delay=0s timeout=1s period=10s #success=1 #failure=3
    Environment:    <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-j8wq2 (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  kube-api-access-j8wq2:
    Type:                    Projected (a volume that contains injected data from multiple sources)
    TokenExpirationSeconds:  3607
    ConfigMapName:           kube-root-ca.crt
    ConfigMapOptional:       <nil>
    DownwardAPI:             true
QoS Class:                   BestEffort
Node-Selectors:              <none>
Tolerations:                 node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
                             node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
  Type    Reason     Age   From               Message
  ----    ------     ----  ----               -------
  Normal  Scheduled  100s  default-scheduler  Successfully assigned dev/pod-nginx to node2
  Normal  Pulled     99s   kubelet            Container image "nginx:1.17.1" already present on machine
  Normal  Created    99s   kubelet            Created container nginx
  Normal  Started    99s   kubelet            Started container nginx
[root@master pod]#
```
# 三、容器探测总结
查看livenessProbe的子属性，除了三种方式，还有一些参数，如下：
```bash
initialDelaySeconds    <integer>    # 容器启动后等待多少秒执行第一次探测
timeoutSeconds         <integer>    # 探测超时时间，默认一秒，最小一秒
periodSeconds          <integer>    # 执行探测的频率，默认是10秒，最小1秒
failureThreshold       <integer>    # 连续探测失败多少次才被认定为失败，默认是3，最小是1
successThreshold       <integer>    # 连续探测成功多少次才被认定为成功，默认是1
```

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