pod生命周期
pod生命周期
我们一般将pod对象从创建至终这段时间范围成为pod的生命周期,它主要包含以下的过程:
- pod创建过程
- 运行初始化容器(init container)过程
- 运行主容器(main container)
- 容器启动后钩子(post start)、容器终止前钩子(pre stop)
- 容器的存活性检测(liveness probe)、就绪性检测(readiness probe)
- pod终止过程
pod的创建和终止
pod的创建过程
- 用户通过kubectl或其他api客户端提交需要创建的pod信息给apiserver
- apiserver开始生成pod对象的信息,并将信息存入etcd,然后返回确认信息至客户端
- apiserver开始反映etcd中pod对象的变化,其他组件使用watch机制来跟踪检查apiserver上的变动
- scheduler发现有新的pod对象要创建,开始为pod分配主机并将结果信息更新至apiserver
- node节点上的kubectl发现有pod调度过来,尝试调用docker启动容器,并将结果返回送至apiserver
- apiserver将接收到的pod状态信息存入etcd中
pod的终止过程
- 用户向apiserver发送删除pod对象的命令
- apiserver中的pod对象信息会随着时间的推移而更新,在宽限期内(默认30s),pod被视为dead
- 将pod标记为terminating状态
- kubelet在监控到pod对象转为terminating状态的同时启动pod关闭进程
- 端点控制器监控到pod对象的关闭行为时将其从所有匹配到此端点的service资源的端点列表移除
- 如果当前pod对象定义了prestop钩子处理器,则在其标记为terminating后即会以同步的方式启动执行
- pod对象中的容器进程收到停止信号
- 宽限期结束后,若pod中还存在仍在运行的进程,那么pod对象会收到立即终止的信号
- kubelet请求apiserver将此pod资源的宽限期设置为0从而完成删除操作,此时pod对于用户已不可见
初始化容器
初始化容器是在pod的主容器启动之前要运行的容器,主要是做一些主容器的前置工作,它具有两大特征
- 初始化容器必须运行完成直至结束,若某初始化容器运行失败,那么k8s需要重启它直到成功完成
- 初始化容器必须按照定义的顺序执行,当仅当前一个执行成功之后,后面的一个才能运行
初始化容器有很多的应用场景,下面列出的是最常见的几个
- 提供主容器镜像中不具备的工具程序或自定义代码
- 初始化容器要先于应用容器串行启动并运行完成,因此可用于延后应用容器的启动直至其依赖的条件得到满足
接下来做一个案例,模拟下面这个需求
假设要以主容器来运行nginx,但是要求在运行nginx之前要能够连接上mysql和redis所在服务器
为了简化测试,事先规定好mysql和redis服务器的地址
创建pod-initcontainer.yaml,内容如下:
apiversion: v1 kind: pod metadata: name: pod-initcontainer namespace: dev labels: user: ayanami spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 initcontainers: - name: test-mysql image: busybox:1.30 command: ['sh','-c','until ping 192.168.145.231 -c 1; do echo waiting for mysql...;sleep 2; done'] - name: test-redis image: busybox:1.30 command: ['sh','-c','until ping 192.168.145.232 -c 1; do echo waiting for redis...;sleep 2; done']
运行配置文件
[root@master ~]# vim pod-initcontainer.yaml [root@master ~]# kubectl create -f pod-initcontainer.yaml pod/pod-initcontainer created [root@master ~]# kubectl get pod pod-initcontainer -n dev name ready status restarts age pod-initcontainer 0/1 init:0/2 0 20s
发现container一直处于初始化状态
此时添加ip地址(注:ens32是你的网卡的名字,不同机器可能不同,可以用ifconfig查看)
[root@master ~]# ifconfig ens32:1 192.168.145.231 netmask 255.255.255.0 up [root@master ~]# ifconfig ens32:2 192.168.145.232 netmask 255.255.255.0 up [root@master ~]# kubectl get pod pod-initcontainer -n dev name ready status restarts age pod-initcontainer 1/1 running 0 19m
发现pod跑起来了
钩子函数
钩子函数能够感知自身生命周期中的事件,并在相应的时刻到来时运行用户指定的程序代码
k8s在主容器的启动之后和停止之前提供了两个钩子函数
- post start:容器创建之后执行,如果失败了会重启容器
- pre stop:容器终止之前执行,执行完成之后容器将成功终止,在其完成之前会阻塞删除容器的操作
钩子处理器支持使用下面三种方式定义动作:
- exec命令:在容器内执行一次命令
...... lifecycle: poststart: exec: command: - cat - /tmp/healthy ......
- tcpsocket:在当前容器尝试访问指定的socket
...... lifecycle: poststart: tcpsocket: port: 8080 ......
- httpget:在当前容器中向某url发起http请求
...... lifecycle: poststart: httpget: path: #uri地址 port: host: scheme: http #支持的协议,http或者https ......
下面演示钩子函数的使用
创建pod-hook-exec.yaml文件,内容如下:
apiversion: v1 kind: pod metadata: name: pod-hook-exec namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 lifecycle: poststart: exec: #在容器启动的时候执行一个命令,修改掉nginx的默认首页内容 command: ["/bin/sh","-c","echo poststart... > /usr/share/nginx/html/index.html"] prestop: #在容器停止之前停止nginx服务 exec: command: ["/usr/sbin/nginx","-s","quit"]
使用配置文件
[root@master ~]# vim pod-hook-exec.yaml [root@master ~]# kubectl create -f pod-hook-exec.yaml pod/pod-hook-exec created [root@master ~]# kubectl get pod pod-hook-exec -n dev -o wide name ready status restarts age ip node nominated node readiness gates pod-hook-exec 1/1 running 0 43s 10.244.2.22 node1 <none> <none> [root@master ~]# curl 10.244.2.22:80 poststart...
容器探测
容器探测用于检测容器中的应用实例是否能正常工作,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k8s就会把该问题实例“摘除”,不承担业务流量,k8s提供了两种探针来实现容器探测,分别是:
- liveness probes:存活性探针,用于检测应用实例当前是否处于正常运行状态,如果不是,k8s会重启容器
- readiness probes:就绪性探针,用于检测应用实例当前是否可以接受请求,如果不能,k8s不会转发流量
即livenessprobe决定是否重启容器,readinesprobe决定是否将请求转发给容器
上面两种探针目前均支持三种探测方式:
- 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
...... livenessprobe: exec: command: - cat - /tmp/healthy ......
- tcpsocket:将会尝试访问同一个用户容器的端口,如果能够建立这条连接,则认为程序正常,否则不正常
...... livenessprobe: tcpsocket: port: 8080 ......
- httpget:调用容器内web应用的url,如果返回的状态码在200和399之间,则认为程序正常,否则不正常
...... lifecycle: poststart: httpget: path: #uri地址 port: host: scheme: http #支持的协议,http或者https ......
下面以liveness probes为例,做几个演示:
方式一:exec
创建pod-liveness-exec.yaml
apiversion: v1 kind: pod metadata: name: pod-liveness-exec namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 livenessprobe: exec: command: ["/bin/cat","/tmp/hello.txt"] #执行一个查看文件的命令
使用配置文件
[root@master ~]# vim pod-liveness-exec.yaml [root@master ~]# kubectl create -f pod-liveness-exec.yaml pod/pod-liveness-exec created [root@master ~]# kubectl get pod pod-liveness-exec -n dev name ready status restarts age pod-liveness-exec 1/1 running 1 102s
发现pod重启了一次,查看错误信息
[root@master ~]# kubectl describe pod pod-liveness-exec -n dev type reason age from message ---- ------ ---- ---- ------- normal scheduled <unknown> default-scheduler successfully assigned dev/pod-liveness-exec to node1 normal pulled 49s (x4 over 2m20s) kubelet, node1 container image "nginx:1.17.1" already present on machine normal created 49s (x4 over 2m20s) kubelet, node1 created container main-container normal started 49s (x4 over 2m20s) kubelet, node1 started container main-container normal killing 49s (x3 over 109s) kubelet, node1 container main-container failed liveness probe, will be restarted warning unhealthy 39s (x10 over 2m9s) kubelet, node1 liveness probe failed: /bin/cat: /tmp/hello.txt: no such file or directory
修改文件内容
apiversion: v1 kind: pod metadata: name: pod-liveness-exec namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 livenessprobe: exec: command: ["/bin/ls","/tmp/"] #执行一个查看文件的命令
使用配置文件
[root@master ~]# vim pod-liveness-exec.yaml [root@master ~]# kubectl delete -f pod-liveness-exec.yaml [root@master ~]# kubectl create -f pod-liveness-exec.yaml pod/pod-liveness-exec created [root@master ~]# kubectl get pod pod-liveness-exec -n dev name ready status restarts age pod-liveness-exec 1/1 running 0 84s
说明没有重启
方式二:tcpsocket
创建pod-liveness-tcpsocket.yaml
apiversion: v1 kind: pod metadata: name: pod-liveness-tcpsocket namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 livenessprobe: tcpsocket: port: 8080 #尝试访问8080端口
使用配置文件
[root@master ~]# vim pod-liveness-tcpsocket.yaml [root@master ~]# kubectl create -f pod-liveness-tcpsocket.yaml pod/pod-liveness-tcpsocket created [root@master ~]# kubectl get pod pod-liveness-tcpsocket -n dev name ready status restarts age pod-liveness-tcpsocket 1/1 running 1 29s
[root@master ~]# kubectl describe pod pod-liveness-tcpsocket -n dev events: type reason age from message ---- ------ ---- ---- ------- normal scheduled <unknown> default-scheduler successfully assigned dev/pod-liveness-tcpsocket to node1 normal pulled 43s (x4 over 2m10s) kubelet, node1 container image "nginx:1.17.1" already present on machine normal created 43s (x4 over 2m10s) kubelet, node1 created container main-container normal started 43s (x4 over 2m10s) kubelet, node1 started container main-container normal killing 43s (x3 over 103s) kubelet, node1 container main-container failed liveness probe, will be restarted warning unhealthy 33s (x10 over 2m3s) kubelet, node1 liveness probe failed: dial tcp 10.244.2.25:8080: connect: connection refused
更改文件内容
apiversion: v1 kind: pod metadata: name: pod-liveness-tcpsocket namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 livenessprobe: tcpsocket: port: 80 #尝试访问80端口
重新使用配置文件
[root@master ~]# vim pod-liveness-tcpsocket.yaml [root@master ~]# kubectl delete -f pod-liveness-tcpsocket.yaml pod "pod-liveness-tcpsocket" deleted [root@master ~]# kubectl create -f pod-liveness-tcpsocket.yaml pod/pod-liveness-tcpsocket created [root@master ~]# kubectl get pod pod-liveness-tcpsocket -n dev name ready status restarts age pod-liveness-tcpsocket 1/1 running 0 18s
表明没有问题
方式三:httpget
创建pod-liveness-httpget.yaml
apiversion: v1 kind: pod metadata: name: pod-liveness-httpget namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 livenessprobe: httpget: #其实就是访问http://127.0.0.1:80/hello scheme: http #支持的协议,http或https port: 80 path: /hello #uri地址
使用配置文件
[root@master ~]# vim pod-liveness-httpget.yaml [root@master ~]# kubectl create -f pod-liveness-httpget.yaml pod/pod-liveness-httpget created [root@master ~]# kubectl get pod pod-liveness-httpget -n dev name ready status restarts age pod-liveness-httpget 1/1 running 1 75s [root@master ~]# kubectl describe pod pod-liveness-httpget -n dev events: type reason age from message ---- ------ ---- ---- ------- normal scheduled <unknown> default-scheduler successfully assigned dev/pod-liveness-httpget to node2 normal pulled 18s (x3 over 74s) kubelet, node2 container image "nginx:1.17.1" already present on machine normal created 18s (x3 over 74s) kubelet, node2 created container main-container normal killing 18s (x2 over 48s) kubelet, node2 container main-container failed liveness probe, will be restarted normal started 17s (x3 over 73s) kubelet, node2 started container main-container warning unhealthy 8s (x7 over 68s) kubelet, node2 liveness probe failed: http probe failed with statuscode: 404
可以看见pod在重启,详细描述说明没找到这个网址
修改配置文件
apiversion: v1 kind: pod metadata: name: pod-liveness-httpget namespace: dev spec: containers: - name: main-container image: nginx:1.17.1 ports: - name: nginx-port containerport: 80 livenessprobe: httpget: #其实就是访问http://127.0.0.1:80/ scheme: http #支持的协议,http或https port: 80 path: / #uri地址
重新使用配置文件
[root@master ~]# kubectl delete -f pod-liveness-httpget.yaml pod "pod-liveness-httpget" deleted [root@master ~]# kubectl create -f pod-liveness-httpget.yaml pod/pod-liveness-httpget created [root@master ~]# kubectl get pod pod-liveness-httpget -n dev name ready status restarts age pod-liveness-httpget 1/1 running 0 24s events: type reason age from message ---- ------ ---- ---- ------- normal scheduled <unknown> default-scheduler successfully assigned dev/pod-liveness-httpget to node2 normal pulled 27s kubelet, node2 container image "nginx:1.17.1" already present on machine normal created 27s kubelet, node2 created container main-container normal started 27s kubelet, node2 started container main-container
表明配置没有问题
其他配置
至此,已经使用liveness probe演示了三种探测方式,但是查看livenessprobe的子属性,会发现除了这三种方式,还有一些其他的配置,在这里一并解释下
[root@master ~]# kubectl explain pod.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> one and only one of the following should be specified. exec specifies the action to take. failurethreshold <integer> 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> 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> 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 and startup. minimum value is 1. tcpsocket <object> tcpsocket specifies an action involving a tcp port. tcp hooks not yet supported timeoutseconds <integer> 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