Kubernetes APIServer 内存爆满
现象
线上Kubernetes集群, 一共5台机器，其中4台机器内存80%+，1台机器内存3.59%， 其中一台master apiserver Node 内存飙升到98%后，OOM掉后，重启了apiserver
问题分析
apiserver内存持续升高，肯定是有资源在堆内存里申请了空间但是没有释放。首先考虑是否是因为建立了太多的链接导致的，使用如下指令查询apiserver链接数：
$ netstat -nat | grep -i "6443" | wc -l
1345
发现链接数在1300+, 对于128Core和745G内存机器多并不算多。
继续分析只能考虑导出kube-apiserver的heap文件来查看其详细的内存分布。
这种方式需要使用go语言包的pprof工具，下面详细讲解go tool pprof 工具的使用以及kube-apiserver的配置
go tool pprof工具使用
kubernetes 1.18这个功能是默认打开的, 但线上集群是1.16, 需要手动打开
$ cat ./manifests/kube-apiserver.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
component: kube-apiserver
tier: control-plane
name: kube-apiserver
namespace: kube-system
spec:
...
- --profiling=true
使用 端口转发，将Pod端口转发到本地端口上
$ kubectl port-forward kube-apiserver-8pmpz 6443:6443
$ go tool pprof http://127.0.0.1:6443/debug/pprof/heap
Fetching profile over HTTP from http://127.0.0.1:6443/debug/pprof/heap
Saved profile in /root/pprof/pprof.kube-apiserver.alloc_objects.alloc_space.inuse_objects.inuse_space.004.pb.gz
File: kube-apiserver
Type: inuse_space
Time: Dec 10, 2020 at 2:46pm (CST)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof)top 20
Showing nodes accounting for 11123.22MB, 95.76% of 11616.18MB total
Dropped 890 nodes (cum <= 58.08MB)
Showing top 20 nodes out of 113
flat flat% sum% cum cum%
9226.15MB 79.43% 79.43% 9226.15MB 79.43% bytes.makeSlice
1122.61MB 9.66% 89.09% 1243.65MB 10.71% k8s.io/kubernetes/vendor/k8s.io/api/core/v1.(*ConfigMap).Unmarshal
139.55MB 1.20% 90.29% 153.05MB 1.32% k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/apis/meta/v1.(*ObjectMeta).Unmarshal
120.53MB 1.04% 91.33% 165.03MB 1.42% encoding/json.(*decodeState).objectInterface
117.29MB 1.01% 92.34% 117.29MB 1.01% reflect.unsafe_NewArray
108.03MB 0.93% 93.27% 108.03MB 0.93% reflect.mapassign
66.51MB 0.57% 93.84% 66.51MB 0.57% k8s.io/kubernetes/vendor/github.com/json-iterator/go.(*Iterator).ReadString
62.51MB 0.54% 94.38% 62.51MB 0.54% k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/registry/generic.ObjectMetaFieldsSet
61.51MB 0.53% 94.91% 61.51MB 0.53% k8s.io/kubernetes/vendor/k8s.io/apiextensions-apiserver/pkg/registry/customresource.objectMetaFieldsSet
43.01MB 0.37% 95.28% 137.03MB 1.18% k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/runtime.structToUnstructured
18MB 0.15% 95.43% 183.61MB 1.58% k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/storage/cacher.(*watchCache).Replace
13.50MB 0.12% 95.55% 137.03MB 1.18% k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/runtime.toUnstructured
9MB 0.077% 95.63% 237.54MB 2.04% k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/apis/meta/v1/unstructured.unstructuredJSONScheme.decodeToUnstructured
7.50MB 0.065% 95.69% 144.53MB 1.24% k8s.io/kubernetes/vendor/k8s.io/apimachinery/pkg/runtime.(*unstructuredConverter).ToUnstructured
6MB 0.052% 95.74% 123.29MB 1.06% reflect.MakeSlice
1.50MB 0.013% 95.76% 8944.02MB 77.00% encoding/json.mapEncoder.encode
看到这边数据到，问题基本明朗了。configmap瞬间大批量操作（平均每个configmap大小在347KB），导致APIServer去list/update configmap时无法一次获取到，就会一直创建slice, 从而使APIServer耗尽内存。
业务请求表现
configmap 和 Pod 业务瞬间瞬间变大，导致host内存耗尽
解决方案
监控好每台机器内存，安全水位线60%，快速扩容apiserver服务
升级1.18以上版本kubernetes，开启
goaway=0.001
