Kubernetes OOM计算规则

kubernetes借助系统的OOM KILL提升服务质量，至于什么是OOM KILL可以去网上搜一下这里不再班门弄斧，下面我们就看一下Kubernetes是按照什么规则来分别设置容器的oom_score_adj。

其实规则也比较简单只有一段代码:

//pkg/kubelet/qos/policy.go
func GetContainerOOMScoreAdjust(pod *v1.Pod, container *v1.Container, memoryCapacity int64) int {
    switch v1qos.GetPodQOS(pod) {
    case v1.PodQOSGuaranteed:
        // Guaranteed containers should be the last to get killed.
        return guaranteedOOMScoreAdj
    case v1.PodQOSBestEffort:
        return besteffortOOMScoreAdj
    }

    // Burstable containers are a middle tier, between Guaranteed and Best-Effort. Ideally,
    // we want to protect Burstable containers that consume less memory than requested.
    // The formula below is a heuristic. A container requesting for 10% of a system's
    // memory will have an OOM score adjust of 900. If a process in container Y
    // uses over 10% of memory, its OOM score will be 1000. The idea is that containers
    // which use more than their request will have an OOM score of 1000 and will be prime
    // targets for OOM kills.
    // Note that this is a heuristic, it won't work if a container has many small processes.
    memoryRequest := container.Resources.Requests.Memory().Value()
    oomScoreAdjust := 1000 - (1000*memoryRequest)/memoryCapacity
    // A guaranteed pod using 100% of memory can have an OOM score of 10. Ensure
    // that burstable pods have a higher OOM score adjustment.
    if int(oomScoreAdjust) < (1000 + guaranteedOOMScoreAdj) {
        return (1000 + guaranteedOOMScoreAdj)
    }
    // Give burstable pods a higher chance of survival over besteffort pods.
    if int(oomScoreAdjust) == besteffortOOMScoreAdj {
        return int(oomScoreAdjust - 1)
    }
    return int(oomScoreAdjust)
}

这段代码就是讲的如何计算每个容器的oom score的。
首先看这个容器所属的Pod是属于什么级别的，如果是Guaranteed级别的直接返回-998也是最高级最后被Kill掉的，如果是BestEffort级别则直接返回1000是最低级别的，最有可能被杀掉。如果是Burstable则是中间级别需要按照资源的申请量来计算oom score。

oomScoreAdjust := 1000 - (1000*memoryRequest)/memoryCapacity

就是这段公式计算出容器的score，最后得到的值会在2-999之间，从这个公式能够看出来Burstable级别的如果越是资源申请的越多则给的分越低，这就意味着容器越不容易被杀掉，如果是申请量越少得出的分越高则越容易被杀掉。