为何设置worker_processes auto的Nginx在低CPU配额下创建50+工作进程？

环境信息 #

Pod资源规格 #

resources:
  requests:
    memory: '512Mi'
    cpu: '200m'
  limits:
    memory: '768Mi'
    cpu: '375m'

Nginx配置 #

worker_processes auto;

events {
    worker_connections 1024;
}

Nginx启动日志 #

2024/02/15 12:17:15 [notice] 32#32: start worker processes
2024/02/15 12:17:15 [notice] 32#32: start worker process 51
2024/02/15 12:17:15 [notice] 32#32: start worker process 52
2024/02/15 12:17:15 [notice] 32#32: start worker process 56
2024/02/15 12:17:15 [notice] 32#32: start worker process 57
2024/02/15 12:17:15 [notice] 32#32: start worker process 58
2024/02/15 12:17:15 [notice] 32#32: start worker process 59
2024/02/15 12:17:15 [notice] 32#32: start worker process 60
2024/02/15 12:17:15 [notice] 32#32: start worker process 61
2024/02/15 12:17:15 [notice] 32#32: start worker process 62
2024/02/15 12:17:15 [notice] 32#32: start worker process 63
2024/02/15 12:17:15 [notice] 32#32: start worker process 64
2024/02/15 12:17:15 [notice] 32#32: start worker process 65
2024/02/15 12:17:15 [notice] 32#32: start worker process 66
2024/02/15 12:17:15 [notice] 32#32: start worker process 67
2024/02/15 12:17:15 [notice] 32#32: start worker process 68
2024/02/15 12:17:15 [notice] 32#32: start worker process 69
2024/02/15 12:17:15 [notice] 32#32: start worker process 70
2024/02/15 12:17:15 [notice] 32#32: start worker process 71
2024/02/15 12:17:15 [notice] 32#32: start worker process 72
2024/02/15 12:17:15 [notice] 32#32: start worker process 73
2024/02/15 12:17:15 [notice] 32#32: start worker process 74
2024/02/15 12:17:15 [notice] 32#32: start worker process 75
2024/02/15 12:17:15 [notice] 32#32: start worker process 76
2024/02/15 12:17:15 [notice] 32#32: start worker process 77
2024/02/15 12:17:15 [notice] 32#32: start worker process 78
2024/02/15 12:17:15 [notice] 32#32: start worker process 79
2024/02/15 12:17:15 [notice] 32#32: start worker process 80
2024/02/15 12:17:15 [notice] 32#32: start worker process 81
2024/02/15 12:17:15 [notice] 32#32: start worker process 82
2024/02/15 12:17:15 [notice] 32#32: start worker process 83
2024/02/15 12:17:15 [notice] 32#32: start worker process 84
2024/02/15 12:17:15 [notice] 32#32: start worker process 85
2024/02/15 12:17:15 [notice] 32#32: start worker process 86
2024/02/15 12:17:15 [notice] 32#32: start worker process 87
2024/02/15 12:17:15 [notice] 32#32: start worker process 88
2024/02/15 12:17:15 [notice] 32#32: start worker process 89
2024/02/15 12:17:15 [notice] 32#32: start worker process 90
2024/02/15 12:17:15 [notice] 32#32: start worker process 91
2024/02/15 12:17:15 [notice] 32#32: start worker process 92
2024/02/15 12:17:15 [notice] 32#32: start worker process 93
2024/02/15 12:17:15 [notice] 32#32: start worker process 94
2024/02/15 12:17:15 [notice] 32#32: start worker process 95
2024/02/15 12:17:15 [notice] 32#32: start worker process 96
2024/02/15 12:17:15 [notice] 32#32: start worker process 97
2024/02/15 12:17:15 [notice] 32#32: start worker process 98
2024/02/15 12:17:15 [notice] 32#32: start worker process 99
2024/02/15 12:17:15 [notice] 32#32: start worker process 100
2024/02/15 12:17:15 [notice] 32#32: start worker process 101
2024/02/15 12:17:15 [notice] 32#32: start worker process 102
2024/02/15 12:17:15 [notice] 32#32: start worker process 103
2024/02/15 12:17:15 [notice] 32#32: start worker process 104
2024/02/15 12:17:15 [notice] 32#32: start worker process 105
2024/02/15 12:17:15 [notice] 32#32: start worker process 106
2024/02/15 12:17:15 [notice] 32#32: start worker process 107
2024/02/15 12:17:15 [notice] 32#32: start worker process 108
2024/02/15 12:17:15 [notice] 32#32: start worker process 109
2024/02/15 12:17:15 [notice] 32#32: start worker process 110
2024/02/15 12:17:15 [notice] 32#32: start worker process 111
2024/02/15 12:17:15 [notice] 32#32: start worker process 112
2024/02/15 12:17:15 [notice] 32#32: start worker process 113
2024/02/15 12:17:15 [notice] 32#32: start worker process 114
2024/02/15 12:17:15 [notice] 32#32: start worker process 115
2024/02/15 12:17:15 [notice] 32#32: start worker process 116
2024/02/15 12:17:15 [notice] 32#32: start worker process 117
2024/02/15 12:17:15 [notice] 32#32: start cache manager process 118
2024/02/15 12:17:15 [notice] 32#32: start cache loader process 119

原因分析 #

Nginx设置worker_processes auto;时，默认会读取宿主机的物理CPU核心数来创建工作进程，完全无视Kubernetes给Pod设置的CPU请求和限制。

从日志里的进程数量来看，你的宿主机应该是一台64核左右的机器——去掉缓存管理和加载进程后，工作进程数正好匹配这个核心数。Nginx启动时直接读取宿主机的/proc/cpuinfo文件获取核心数，根本不会识别Kubernetes的CPU配额。

这种情况会引发两个严重问题：

• 大量Nginx工作进程在只有0.375核CPU配额的Pod内争抢资源，进程频繁被调度，性能大幅下降
• 超出Pod的CPU限制后，Kubernetes会触发CPU节流（throttling），进一步恶化性能

解决办法 #

• 手动设置worker_processes为合理值，比如根据Pod的CPU限制设置为1或2：worker_processes 1;
• 如果需要动态适配，可以通过启动脚本读取Kubernetes的CPU配额环境变量（比如KUBERNETES_CPU_LIMIT），在启动Nginx前自动生成配置文件，设置对应的worker进程数

内容的提问来源于stack exchange，提问作者bhantol