// Start eager background caching of volume stats.
func (s *fsResourceAnalyzer) Start() {
    s.startOnce.Do(func() {
        if s.calcPeriod <= 0 {
            klog.Info("Volume stats collection disabled.")
            return
        }
        klog.Info("Starting FS ResourceAnalyzer")
        go wait.Forever(func() { s.updateCachedPodVolumeStats() }, s.calcPeriod)
    })
}

// updateCachedPodVolumeStats calculates and caches the PodVolumeStats for every Pod known to the kubelet.
func (s *fsResourceAnalyzer) updateCachedPodVolumeStats() {
    oldCache := s.cachedVolumeStats.Load().(statCache)
    newCache := make(statCache)

    // Copy existing entries to new map, creating/starting new entries for pods missing from the cache
    for _, pod := range s.statsProvider.GetPods() {
        if value, found := oldCache[pod.GetUID()]; !found {
            newCache[pod.GetUID()] = newVolumeStatCalculator(s.statsProvider, s.calcPeriod, pod).StartOnce()
        } else {
            newCache[pod.GetUID()] = value
        }
    }

    // Stop entries for pods that have been deleted
    for uid, entry := range oldCache {
        if _, found := newCache[uid]; !found {
            entry.StopOnce()
        }
    }

    // Update the cache reference
    s.cachedVolumeStats.Store(newCache)
}

之前的指标定义
var someMetricDefinition = prometheus.CounterOpts{
    Name: "some_metric",
    Help: "some description",
}
新版中加入了StabilityLevel和DeprecatedVersion两个字段
var deprecatedMetricDefinition = kubemetrics.CounterOpts{
    Name: "some_deprecated_metric",
    Help: "some description",
    StabilityLevel: kubemetrics.STABLE, // this is also a custom metadata field
    DeprecatedVersion: "1.15", // this is a custom metadata field
}

弃用前：

# HELP some_counter this counts things
# TYPE some_counter counter
some_counter 0
弃用后：

# HELP some_counter (Deprecated since 1.15.0) this counts things
# TYPE some_counter counter
some_counter 0