了解k8s中的Liveness和Readiness
Liveness:
表明是否容器正在运行。如果liveness探测为fail，则kubelet会kill掉容器，并且会触发restart设置的策略。默认不设置的情况下，该状态为success. Readiness: 表明容器是否可以接受服务请求。如果readiness探测失败，则endpoints控制器会从endpoints中摘除该Pod IP。在初始化延迟探测时间之前，默认是Failure。如果没有设置readiness探测，该状态为success。代码分析
基于Kubernetes 1.11.0
1.启动探测
在kubelet启动是时候会启动健康检查的探测：
kubelet.go中Run方法...kl.probeManager.Start() //启动探测服务...
2.看一下probeManager都做了哪些事情
prober_manager.go中我们看一下这段代码：
// Manager manages pod probing. It creates a probe "worker" for every container that specifies a// probe (AddPod). The worker periodically probes its assigned container and caches the results. The// manager use the cached probe results to set the appropriate Ready state in the PodStatus when// requested (UpdatePodStatus). Updating probe parameters is not currently supported.// TODO: Move liveness probing out of the runtime, to here.type Manager interface { // AddPod creates new probe workers for every container probe. This should be called for every // pod created. AddPod(pod *v1.Pod) // RemovePod handles cleaning up the removed pod state, including terminating probe workers and // deleting cached results. RemovePod(pod *v1.Pod) // CleanupPods handles cleaning up pods which should no longer be running. // It takes a list of "active pods" which should not be cleaned up. CleanupPods(activePods []*v1.Pod) // UpdatePodStatus modifies the given PodStatus with the appropriate Ready state for each // container based on container running status, cached probe results and worker states. UpdatePodStatus(types.UID, *v1.PodStatus) // Start starts the Manager sync loops. Start()} 这是一个Manager的接口声明，该Manager负载pod的探测。当执行AddPod时，会为Pod中每一个容器创建一个执行探测任务的worker, 该worker会对所分配的容器进行周期性的探测，并把探测结果缓存。当UpdatePodStatus方法执行时，该manager会使用探测的缓存结果设置PodStatus为近似Ready的状态：
3.一“探”究竟
先看一下探测的struct
type Probe struct { // The action taken to determine the health of a container Handler `json:",inline" protobuf:"bytes,1,opt,name=handler"` // 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 // +optional InitialDelaySeconds int32 `json:"initialDelaySeconds,omitempty" protobuf:"varint,2,opt,name=initialDelaySeconds"` // 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 // +optional TimeoutSeconds int32 `json:"timeoutSeconds,omitempty" protobuf:"varint,3,opt,name=timeoutSeconds"` // How often (in seconds) to perform the probe. // Default to 10 seconds. Minimum value is 1. // +optional PeriodSeconds int32 `json:"periodSeconds,omitempty" protobuf:"varint,4,opt,name=periodSeconds"` // Minimum consecutive successes for the probe to be considered successful after having failed. // Defaults to 1. Must be 1 for liveness. Minimum value is 1. // +optional SuccessThreshold int32 `json:"successThreshold,omitempty" protobuf:"varint,5,opt,name=successThreshold"` // Minimum consecutive failures for the probe to be considered failed after having succeeded. // Defaults to 3. Minimum value is 1. // +optional FailureThreshold int32 `json:"failureThreshold,omitempty" protobuf:"varint,6,opt,name=failureThreshold"`} initialDelaySeconds: 表示容器启动之后延迟多久进行liveness探测
timeoutSeconds：每次执行探测的超时时间 periodSeconds：探测的周期时间 successThreshold：最少连续几次探测成功的次数，满足该次数则认为success。 failureThreshold：最少连续几次探测失败的次数，满足该次数则认为failHandler:
不论是liveness还是readiness都支持3种类型的探测方式：执行命令、http方式以及tcp方式。// Handler defines a specific action that should be taken// TODO: pass structured data to these actions, and document that data here.type Handler struct { // One and only one of the following should be specified. // Exec specifies the action to take. // +optional Exec *ExecAction `json:"exec,omitempty" protobuf:"bytes,1,opt,name=exec"` // HTTPGet specifies the http request to perform. // +optional HTTPGet *HTTPGetAction `json:"httpGet,omitempty" protobuf:"bytes,2,opt,name=httpGet"` // TCPSocket specifies an action involving a TCP port. // TCP hooks not yet supported // TODO: implement a realistic TCP lifecycle hook // +optional TCPSocket *TCPSocketAction `json:"tcpSocket,omitempty" protobuf:"bytes,3,opt,name=tcpSocket"`} 接下来看一下prober.go中的runProbe方法。
func (pb *prober) runProbe(probeType probeType, p *v1.Probe, pod *v1.Pod, status v1.PodStatus, container v1.Container, containerID kubecontainer.ContainerID) (probe.Result, string, error) { timeout := time.Duration(p.TimeoutSeconds) * time.Second if p.Exec != nil { glog.V(4).Infof("Exec-Probe Pod: %v, Container: %v, Command: %v", pod, container, p.Exec.Command) command := kubecontainer.ExpandContainerCommandOnlyStatic(p.Exec.Command, container.Env) return pb.exec.Probe(pb.newExecInContainer(container, containerID, command, timeout)) } if p.HTTPGet != nil { scheme := strings.ToLower(string(p.HTTPGet.Scheme)) host := p.HTTPGet.Host if host == "" { host = status.PodIP } port, err := extractPort(p.HTTPGet.Port, container) if err != nil { return probe.Unknown, "", err } path := p.HTTPGet.Path glog.V(4).Infof("HTTP-Probe Host: %v://%v, Port: %v, Path: %v", scheme, host, port, path) url := formatURL(scheme, host, port, path) headers := buildHeader(p.HTTPGet.HTTPHeaders) glog.V(4).Infof("HTTP-Probe Headers: %v", headers) if probeType == liveness { return pb.livenessHttp.Probe(url, headers, timeout) } else { // readiness return pb.readinessHttp.Probe(url, headers, timeout) } } if p.TCPSocket != nil { port, err := extractPort(p.TCPSocket.Port, container) if err != nil { return probe.Unknown, "", err } host := p.TCPSocket.Host if host == "" { host = status.PodIP } glog.V(4).Infof("TCP-Probe Host: %v, Port: %v, Timeout: %v", host, port, timeout) return pb.tcp.Probe(host, port, timeout) } glog.Warningf("Failed to find probe builder for container: %v", container) return probe.Unknown, "", fmt.Errorf("Missing probe handler for %s:%s", format.Pod(pod), container.Name)} 1.执行命令方式
通过newExecInContainer方法调用CRI执行命令：
// ExecAction describes a "run in container" action.type ExecAction struct { // Command is the command line to execute inside the container, the working directory for the // command is root ('/') in the container's filesystem. The command is simply exec'd, it is // not run inside a shell, so traditional shell instructions ('|', etc) won't work. To use // a shell, you need to explicitly call out to that shell. // Exit status of 0 is treated as live/healthy and non-zero is unhealthy. // +optional Command []string `json:"command,omitempty" protobuf:"bytes,1,rep,name=command"`} 2.http GET方式
通过http GET方式进行探测。 Port：表示访问容器的端口 Host：表示访问的主机，默认是Pod IP// HTTPGetAction describes an action based on HTTP Get requests.type HTTPGetAction struct { // Path to access on the HTTP server. // +optional Path string `json:"path,omitempty" protobuf:"bytes,1,opt,name=path"` // Name or number of the port to access on the container. // Number must be in the range 1 to 65535. // Name must be an IANA_SVC_NAME. Port intstr.IntOrString `json:"port" protobuf:"bytes,2,opt,name=port"` // Host name to connect to, defaults to the pod IP. You probably want to set // "Host" in httpHeaders instead. // +optional Host string `json:"host,omitempty" protobuf:"bytes,3,opt,name=host"` // Scheme to use for connecting to the host. // Defaults to HTTP. // +optional Scheme URIScheme `json:"scheme,omitempty" protobuf:"bytes,4,opt,name=scheme,casttype=URIScheme"` // Custom headers to set in the request. HTTP allows repeated headers. // +optional HTTPHeaders []HTTPHeader `json:"httpHeaders,omitempty" protobuf:"bytes,5,rep,name=httpHeaders"`} 3.tcp方式
通过设置主机和端口即可进行tcp方式访问// TCPSocketAction describes an action based on opening a sockettype TCPSocketAction struct { // Number or name of the port to access on the container. // Number must be in the range 1 to 65535. // Name must be an IANA_SVC_NAME. Port intstr.IntOrString `json:"port" protobuf:"bytes,1,opt,name=port"` // Optional: Host name to connect to, defaults to the pod IP. // +optional Host string `json:"host,omitempty" protobuf:"bytes,2,opt,name=host"`} 此处脑洞一下：如果三种探测方式都设置了，会如何执行处理？
思考
通过k8s部署生产环境应用时，建议设置上liveness和readiness, 这也是保障服务稳定性的最佳实践。
另外由于Pod Ready不能保证实际的业务应用Ready可用，在最新的 1.14 版本中新增了一个Pod Readiness Gates 特性 。通过这个特性，可以保证应用Ready后进而设置Pod Ready。 结尾
针对上面的脑洞：如果三种探测方式都设置了，会如何执行处理？
答：我们如果在Pod中设置多个探测方式，提交配置的时候会直接报错：
此处继续源代码：在validation.go中validateHandler中进行了限制(也为上面Handler struct提到的"One and only one of the following should be specified."提供了事实依据) func validateHandler(handler *core.Handler, fldPath *field.Path) field.ErrorList { numHandlers := 0 allErrors := field.ErrorList{} if handler.Exec != nil { if numHandlers > 0 { allErrors = append(allErrors, field.Forbidden(fldPath.Child("exec"), "may not specify more than 1 handler type")) } else { numHandlers++ allErrors = append(allErrors, validateExecAction(handler.Exec, fldPath.Child("exec"))...) } } if handler.HTTPGet != nil { if numHandlers > 0 { allErrors = append(allErrors, field.Forbidden(fldPath.Child("httpGet"), "may not specify more than 1 handler type")) } else { numHandlers++ allErrors = append(allErrors, validateHTTPGetAction(handler.HTTPGet, fldPath.Child("httpGet"))...) } } if handler.TCPSocket != nil { if numHandlers > 0 { allErrors = append(allErrors, field.Forbidden(fldPath.Child("tcpSocket"), "may not specify more than 1 handler type")) } else { numHandlers++ allErrors = append(allErrors, validateTCPSocketAction(handler.TCPSocket, fldPath.Child("tcpSocket"))...) } } if numHandlers == 0 { allErrors = append(allErrors, field.Required(fldPath, "must specify a handler type")) } return allErrors} 本文为云栖社区原创内容，未经允许不得转载。