Liveness探测
Liveness 探测让用户可以自定义判断容器是否健康的条件。如果探测失败，Kubernetes 就会重启容器。
第一步：创建如下 Pod：
[root@master-01 k8s]# vim liveness.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: myapp-healthy
namespace: default
spec:
replicas: 1
apiVersion: apps/v1
kind: Deployment
metadata:
name: myapp-healthy
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app: myapp
release: canary
template:
metadata:
labels:
app: myapp
release: canary
spec:
imagePullSecrets:
- name: regsecret
hostAliases:
- ip: "10.1.1.5"
hostnames:
- "harbor-ali.abc.com"
containers:
- name: myapp
image: "harbor-ali.abc.com/k8s_img/myapp:v1"
imagePullPolicy: Always
ports:
- name: http
containerPort: 80
args:
- /bin/sh
- -c
- touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 400
livenessProbe:
exec:
command:
- cat
- /tmp/healthy
initialDelaySeconds: 10
periodSeconds: 5
nodeSelector:
node-label: test
启动进程首先创建文件 /tmp/healthy，30 秒后删除，在我们的设定中，如果 /tmp/healthy 文件存在，则认为容器处于正常状态，反正则发生故障。
livenessProbe 部分定义如何执行 Liveness 探测：
探测的方法是：通过 cat 命令检查 /tmp/healthy 文件是否存在。如果命令执行成功，返回值为零，Kubernetes 则认为本次 Liveness 探测成功；如果命令返回值非零，本次 Liveness 探测失败。
initialDelaySeconds: 10 指定容器启动 10 之后开始执行 Liveness 探测，我们一般会根据应用启动的准备时间来设置。比如某个应用正常启动要花 30 秒，那么 initialDelaySeconds 的值就应该大于 30。
periodSeconds: 5 指定每 5 秒执行一次 Liveness 探测。Kubernetes 如果连续执行 3 次 Liveness 探测均失败，则会杀掉并重启容器。
第二步：下面创建 Pod liveness：
[root@master-01 k8s]# kubectl apply -f liveness.yaml
deployment.apps/myapp-healthy created
[root@master-01 k8s]# kubectl get pod
NAME READY STATUS RESTARTS AGE
myapp-healthy-5cd98cfb54-hw7m9 1/1 Running 0 5s
从配置文件可知，最开始的 30 秒，/tmp/healthy 存在，cat 命令返回 0，Liveness 探测成功
第三步：这段时间 kubectl describe pod 的 Events部分会显示正常的日志。
[root@master-01 k8s]# kubectl describe pod myapp-healthy-5cd98cfb54-hw7m9
...
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled default-scheduler Successfully assigned default/myapp-healthy-6654757bc6-lcjj2 to node-02
Normal Pulling 15s kubelet, node-02 Pulling image "harbor-ali.abc.com/k8s_img/myapp:v1"
Normal Pulled 15s kubelet, node-02 Successfully pulled image "harbor-ali.abc.com/k8s_img/myapp:v1"
Normal Created 15s kubelet, node-02 Created container myapp
Normal Started 15s kubelet, node-02 Started container myapp
第四步：33秒后再次查看日志
33 秒之后，日志会显示 /tmp/healthy 已经不存在，Liveness 探测失败。再过几十秒，几次探测都失败后，容器会被重启。
[root@master-01 k8s]# kubectl describe pod myapp-healthy-5cd98cfb54-hw7m9
...
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled default-scheduler Successfully assigned default/myapp-healthy-6654757bc6-lcjj2 to node-02
Normal Pulling 33s kubelet, node-02 Pulling image "harbor-ali.abc.com/k8s_img/myapp:v1"
Normal Pulled 33s kubelet, node-02 Successfully pulled image "harbor-ali.abc.com/k8s_img/myapp:v1"
Normal Created 33s kubelet, node-02 Created container myapp
Normal Started 33s kubelet, node-02 Started container myapp
Warning Unhealthy 0s kubelet, node-02 Liveness probe failed: cat: can't open '/tmp/healthy': No such file or directory
第五步：查看pod
可以发现容器开始被重启
[root@master-01 k8s]# kubectl get pod
NAME READY STATUS RESTARTS AGE
myapp-healthy-6654757bc6-lcjj2 1/1 Running 1 80s
Readiness 探测
除了 Liveness 探测，Kubernetes Health Check 机制还包括 Readiness 探测。
用户通过 Liveness 探测可以告诉 Kubernetes 什么时候通过重启容器实现自愈；Readiness 探测则是告诉 Kubernetes 什么时候可以将容器加入到 Service 负载均衡池中，对外提供服务。
第一步：Readiness 探测的配置语法与 Liveness 探测完全一样
这个配置文件只是将前面例子中的 liveness 替换为了 readiness，我们看看有什么不同的效果。
[root@master-01 healthy]# cat readiness.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: myapp-readiness
namespace: default
spec:
replicas: 1
selector:
matchLabels:
app: myapp
release: canary
template:
metadata:
labels:
app: myapp
release: canary
spec:
imagePullSecrets:
- name: regsecret
hostAliases:
- ip: "10.1.1.5"
hostnames:
- "harbor-ali.abc.com"
containers:
- name: myapp
image: "harbor-ali.abc.com/k8s_img/myapp:v1"
imagePullPolicy: Always
ports:
- name: http
containerPort: 80
args:
- /bin/sh
- -c
- touch /tmp/healthy; sleep 30; rm -rf /tmp/healthy; sleep 400
readinessProbe:
exec:
command:
- cat
- /tmp/healthy
initialDelaySeconds: 10
periodSeconds: 5
nodeSelector:
node-label: test
第二步：部署
[root@master-01 healthy]# kubectl get pod
NAME READY STATUS RESTARTS AGE
myapp-readiness-6bdd66f6cd-p2j4g 0/1 Running 0 3s
[root@master-01 healthy]# kubectl get pod myapp-readiness-6bdd66f6cd-5fvw5
NAME READY STATUS RESTARTS AGE
myapp-readiness-6bdd66f6cd-5fvw5 1/1 Running 0 15s
[root@master-01 healthy]# kubectl get pod myapp-readiness-6bdd66f6cd-5fvw5
NAME READY STATUS RESTARTS AGE
myapp-readiness-6bdd66f6cd-5fvw5 0/1 Running 0 43s
Pod readiness 的 READY 状态经历了如下变化：
刚被创建时，READY 状态为不可用。
15 秒后（initialDelaySeconds + periodSeconds），第一次进行 Readiness 探测并成功返回，设置 READY 为可用。
30 秒后，/tmp/healthy 被删除，连续 3 次 Readiness 探测均失败后，READY 被设置为不可用。
第三步：通过 kubectl describe pod readiness 也可以看到 Readiness 探测失败的日志。
[root@master-01 healthy]# kubectl describe pod myapp-readiness-6bdd66f6cd-5fvw5
···
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled default-scheduler Successfully assigned default/myapp-readiness-6bdd66f6cd-5fvw5 to node-02
Normal Pulling 2m50s kubelet, node-02 Pulling image "harbor-ali.abc.com/k8s_img/myapp:v1"
Normal Pulled 2m50s kubelet, node-02 Successfully pulled image "harbor-ali.abc.com/k8s_img/myapp:v1"
Normal Created 2m50s kubelet, node-02 Created container myapp
Normal Started 2m50s kubelet, node-02 Started container myapp
Warning Unhealthy 39s (x21 over 43s) kubelet, node-02 Readiness probe failed: cat: can't open '/tmp/healthy': No such file or directory
下面对 Liveness 探测和 Readiness 探测做个比较：
Liveness 探测和 Readiness 探测是两种 Health Check 机制，如果不特意配置，Kubernetes 将对两种探测采取相同的默认行为，即通过判断容器启动进程的返回值是否为零来判断探测是否成功。
两种探测的配置方法完全一样，支持的配置参数也一样。不同之处在于探测失败后的行为：Liveness 探测是重启容器；Readiness 探测则是将容器设置为不可用，不接收 Service 转发的请求。
Liveness 探测和 Readiness 探测是独立执行的，二者之间没有依赖，所以可以单独使用，也可以同时使用。用 Liveness 探测判断容器是否需要重启以实现自愈；用 Readiness 探测判断容器是否已经准备好对外提供服务。
转自：http://www.kendd.cn/?p=708