periodSeconds和timeoutSecondskubernetes probes的配置中有两个容易混淆的参数，periodSeconds和timeoutSeconds，其配置方式如下：
apiVersion: v1
kind: Pod
metadata:
name: darwin-app
spec:
containers:
- name: darwin-container
image: darwin-image
livenessProbe:
httpGet:
path: /darwin-path
port: 8080
initialDelaySeconds: 60
periodSeconds: 10
timeoutSeconds: 5
failureThreshold: 3
官方对这两个参数的解释如下：
periodSeconds: How often (in seconds) to perform the probe. Default to 10 seconds. The minimum value is 1.timeoutSeconds: Number of seconds after which the probe times out. Defaults to 1 second. Minimum value is 1.
意思是说periodSeconds表示执行探针的周期，而timeoutSeconds表示执行探针的超时时间。
网上有不少针对这两个参数的讨论(如下)，其中涉及到一个问题，如果timeoutSeconds > periodSeconds 会怎么样？
其中在上面的第3篇中对timeoutSeconds>periodSeconds的情况有如下描述，即在这种情况下，如果探针超时，则探针周期等于timeoutSeconds。那么这种说法是否正确呢？
If you had the opposite (
timeoutSeconds=10,periodSeconds=5), then the probes would look as follows:0s: liveness probe initiated 10s: liveness probe times out 10s: liveness probe initiated again
鉴于网上众说纷纭，我们通过源码来一探究竟。
kubernetes的探针机制是由kubelet执行的，目前支持exec、grpc、httpGet、tcpSocket这4种探针方式。
探针的代码逻辑并不复杂，以v1.30.2的代码为例，其入口函数如下，可以看到它会启动一个周期为w.spec.PeriodSeconds(即探针中定义的periodSeconds)定时器，周期性地执行探针。
// run periodically probes the container.
func (w *worker) run() {
ctx := context.Background()
probeTickerPeriod := time.Duration(w.spec.PeriodSeconds) * time.Second
...
probeTicker := time.NewTicker(probeTickerPeriod)
...
probeLoop:
for w.doProbe(ctx) {
// Wait for next probe tick.
select {
case <-w.stopCh:
break probeLoop
case <-probeTicker.C:
case <-w.manualTriggerCh:
// continue
}
}
}
现在已经找到periodSeconds的用途，下一步需要找到timeoutSeconds。
首先进入doProbe函数，它调用了w.probeManager.prober.probe：
// doProbe probes the container once and records the result.
// Returns whether the worker should continue.
func (w *worker) doProbe(ctx context.Context) (keepGoing bool) {
...
// Note, exec probe does NOT have access to pod environment variables or downward API
result, err := w.probeManager.prober.probe(ctx, w.probeType, w.pod, status, w.container, w.containerID)
if err != nil {
// Prober error, throw away the result.
return true
}
...
}
下面的probe函数用于执行一个特定的探针。需要注意的是，它调用了pb.runProbeWithRetries，其中maxProbeRetries值为3，说明在一个周期(periodSeconds)中最多可以执行3次探针命令：
// probe probes the container.
func (pb *prober) probe(ctx context.Context, probeType probeType, pod *v1.Pod, status v1.PodStatus, container v1.Container, containerID kubecontainer.ContainerID) (results.Result, error) {
var probeSpec *v1.Probe
switch probeType {
case readiness:
probeSpec = container.ReadinessProbe
case liveness:
probeSpec = container.LivenessProbe
case startup:
probeSpec = container.StartupProbe
default:
return results.Failure, fmt.Errorf("unknown probe type: %q", probeType)
}
...
result, output, err := pb.runProbeWithRetries(ctx, probeType, probeSpec, pod, status, container, containerID, maxProbeRetries)
...
}
runProbeWithRetries的注释说明，可能会执行多次探针，直到探针返回成功或全部尝试失败：
// runProbeWithRetries tries to probe the container in a finite loop, it returns the last result
// if it never succeeds.
func (pb *prober) runProbeWithRetries(ctx context.Context, probeType probeType, p *v1.Probe, pod *v1.Pod, status v1.PodStatus, container v1.Container, containerID kubecontainer.ContainerID, retries int) (probe.Result, string, error) {
...
for i := 0; i < retries; i++ {
result, output, err = pb.runProbe(ctx, probeType, p, pod, status, container, containerID)
...
}
...
}
在runProbe函数中，最终找到了timeoutSeconds对应的参数p.TimeoutSeconds，其作为各个探针命令的超时参数，如在httpGet类型的探针中，它作为了httpClient的请求超时时间：
func (pb *prober) runProbe(ctx context.Context, 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 {
command := kubecontainer.ExpandContainerCommandOnlyStatic(p.Exec.Command, container.Env)
return pb.exec.Probe(pb.newExecInContainer(ctx, container, containerID, command, timeout))
}
if p.HTTPGet != nil {
req, err := httpprobe.NewRequestForHTTPGetAction(p.HTTPGet, &container, status.PodIP, "probe")
...
return pb.http.Probe(req, timeout)
}
if p.TCPSocket != nil {
port, err := probe.ResolveContainerPort(p.TCPSocket.Port, &container)
...
host := p.TCPSocket.Host
if host == "" {
host = status.PodIP
}
return pb.tcp.Probe(host, port, timeout)
}
if utilfeature.DefaultFeatureGate.Enabled(kubefeatures.GRPCContainerProbe) && p.GRPC != nil {
host := status.PodIP
service := ""
if p.GRPC.Service != nil {
service = *p.GRPC.Service
}
return pb.grpc.Probe(host, service, int(p.GRPC.Port), timeout)
}
...
}
至此我们可以拼接出periodSeconds和timeoutSeconds的关系，其逻辑关系与如下代码类似。
probeTicker := time.NewTicker(periodSeconds)
for {
select {
case <-probeTicker.C:
for i := 0; i < 3; i++ {
if ok:=probe(timeoutSeconds);ok{
return
}
}
}
periodSeconds用于启动一个周期性调用探针命令的定时器，而timeoutSeconds作为探针命令的超时参数timeoutSeconds和periodSeconds之间并没有明确的关系。如果timeoutSeconds=10s，periodSeconds=5s，则本次探针周期可能为[5s, 30s)之内的任意值，并不是该文中说的periodSeconds=timeoutSeconds(由于本文写于3年前，经查阅v1.19.10版本代码，逻辑上与现有版本代码相同。)/hleathz http endpoint是否可以访问等，因此建议将timeoutSeconds设置为一个小于periodSeconds的合理的值。failureThreshold/successThreshold和maxProbeRetries的关系maxProbeRetries用于定义一次探针周期内探针命令执行的最大尝试次数；successThreshold 加1，反之failureThreshold加1；