1.Init 容器可以包含一些安装过程中应用容器中不存在的实用工具或个性化代码。

    2.Init 容器可以安全地运行这些工具，避免这些工具导致应用镜像的安全性降低。

    3.应用镜像的创建者和部署者可以各自独立工作，而没有必要联合构建一个单独的应用镜像。

    4.Init 容器能以不同于 Pod 内应用容器的文件系统视图运行。因此， Init 容器可具有访问 Secrets 的权限，而应用容器不能够访问。

    5.由于 Init 容器必须在应用容器启动之前运行完成，因此 Init 容器提供了一种机制来阻塞或延迟应用容器的启动，直到满足了一组先决条件。一旦前置条件满足，Pod 内的所有的应用容器会并行启动。

[root@k8s-master ~]# vim pod.yml
apiVersion: v1
kind: Pod
metadata:
labels:
name: initpod
name: initpod
spec:
containers:
- image: myapp:v1
name: myapp
initContainers:
- name: init-myservice
image: busybox
command: ["sh","-c","until test -e /testfile;do echo wating for myservice;
sleep 2;done"]
[root@k8s-master ~]# kubectl apply -f pod.yml
pod/initpod created
[root@k8s-master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
initpod 0/1 Init:0/1 0 3s
[root@k8s-master ~]# kubectl logs pods/initpod init-myservice
wating for myservice
wating for myservice
wating for myservice
wating for myservice
wating for myservice
wating for myservice
[root@k8s-master ~]# kubectl exec pods/initpod -c init-myservice -- /bin/sh -c
"touch /testfile"
[root@k8s-master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
initpod 1/1 Running 0 62s

探针

存活探针

[root@k8s-master ~]# vim pod.yml
apiVersion: v1
kind: Pod
metadata:
labels:
name: liveness
name: liveness
spec:
containers:
- image: myapp:v1
name: myapp
livenessProbe:
tcpSocket: #检测端口存在性
port: 8080
initialDelaySeconds: 3 #容器启动后要等待多少秒后就探针开始工作，默认是 0
periodSeconds: 1 #执行探测的时间间隔，默认为 10s
timeoutSeconds: 1 #探针执行检测请求后，等待响应的超时时间，默认为 1s
#测试：
[root@k8s-master ~]# kubectl apply -f pod.yml
pod/liveness created
[root@k8s-master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
liveness 0/1 CrashLoopBackOff 2 (7s ago) 22s
[root@k8s-master ~]# kubectl describe pods
Warning Unhealthy 1s (x9 over 13s) kubelet Liveness probe failed:
dial tcp 10.244.2.6:8080: connect: connection refused

就绪探针

[root@k8s-master ~]# vim pod.yml
apiVersion: v1
kind: Pod
metadata:
labels:
name: readiness
name: readiness
spec:
containers:
- image: myapp:v1
name: myapp
readinessProbe:
httpGet:
path: /test.html
port: 80
initialDelaySeconds: 1
periodSeconds: 3
timeoutSeconds: 1
#测试：
[root@k8s-master ~]# kubectl expose pod readiness --port 80 --target-port 80
[root@k8s-master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
readiness 0/1 Running 0 5m25s
[root@k8s-master ~]# kubectl describe pods readiness
Warning Unhealthy 26s (x66 over 5m43s) kubelet Readiness probe
failed: HTTP probe failed with statuscode: 404
[root@k8s-master ~]# kubectl describe services readiness
Name: readiness
Namespace: default
Labels: name=readiness
Annotations: <none>
Selector: name=readiness
Type: ClusterIP
IP Family Policy: SingleStack
IP Families: IPv4
IP: 10.100.171.244
IPs: 10.100.171.244
Port: <unset> 80/TCP
TargetPort: 80/TCP
Endpoints: #没有暴漏端口，就绪探针探测不满足暴漏
条件
Session Affinity: None
Events: <none>
kubectl exec pods/readiness -c myapp -- /bin/sh -c "echo test >
/usr/share/nginx/html/test.html"
[root@k8s-master ~]# kubectl get pods
NAME READY STATUS RESTARTS AGE
readiness 1/1 Running 0 7m49s
[root@k8s-master ~]# kubectl describe services readiness
Name: readiness
Namespace: default
Labels: name=readiness
Annotations: <none>
Selector: name=readiness
Type: ClusterIP
IP Family Policy: SingleStack
IP Families: IPv4
IP: 10.100.171.244
IPs: 10.100.171.244
Port: <unset> 80/TCP
TargetPort: 80/TCP
Endpoints: 10.244.2.8:80 #满组条件端口暴漏
Session Affinity: None
Events: <none>