2022-02-01 8a3d1c126aec174d9afe0d4ad57dfbc5 99+ 30 分钟 4.5 k0次访问

关于Kubernetes集群中常见问题的排查方法的一些笔记

一切时代的艺术都在努力为我们内心那神圣的无声的欲望提供语言。 ——赫尔曼·黑塞《彼得·卡门青》

写在前面

学习K8s，所以整理记忆
文章理论内容来源于：
《Kubernetes权威指南:从Docker到Kubernetes实践全接触》第四版.第十一章
这里整理学习笔记

一切时代的艺术都在努力为我们内心那神圣的无声的欲望提供语言。 ——赫尔曼·黑塞《彼得·卡门青》

因为没有具体的Demo，所以文章有些空，类似于一些指导思想，读着乏味，这里先列出干货：一些查问题的网站，关于内容之后有机会在补充相关的案例，如果解决问题，时间紧张的小伙伴还是针对问题描述下面的平台里找找

查问题的网站
`Kubernetes`官网中监控、记录和调试相关问题: https://kubernetes.io/docs/tasks/debug-application-cluster/
`Kubernetes`官方论坛: https://discuss.kubernetes.io/(这个需要科学上网)
`GitHub`库关于`Kubernetes`问题列表:https://github.com/kubernetes/kubernetes/issues
`StackOverflow`网站上关于`Kubernetes`的问题讨论：https://stackoverflow.com/questions/tagged/kubernetes
`Kubernetes Slack`聊天群组: https://kubernetes.slack.com/(需要谷歌账号)

Kubernetes集群中常见问题的排查方法

为了跟踪和发现在Kubernetes集群中运行的容器应用出现的问题,我们常用如下查错方法。

查看Kubernetes对象的当前运行时信息,特别是与对象关联的Event事件。这些事件记录了相关主题、发生时间、最近发生时间、发生次数及事件原因等,对排查故障非常有价值。通过查看对象的运行时数据,我们还可以发现参数错误、关联错误、状态异常等明显问题。由于在Kubernetes中多种对象相互关联,因此这一步可能会涉及多·个相关对象的排查问题。

对于服务、容器方面的问题,可能需要深入容器内部进行故障诊断,此时可以通过查看容器的运行日志来定位具体问题。

对于某些复杂问题,例如Pod调度这种全局性的问题,可能需要结合集群中每个节点上的Kubernetes服务日志来排查。比如搜集Master上的kube-apiserver, kube-schedule, kube-controler-manager服务日志,以及各个Node上的kubelet, kube-proxy服务日志.

查看系统Event

在Kubernetes集群中创建Pod后,我们可以通过kubectl get pods命令查看Pod列表,但通过该命令显示的信息有限。Kubernetes提供了kubectl describe pod命令来查看一个Pod的详细信息,例如:

通过kubectl describe pod命令,可以显示Pod创建时的配置定义、状态等信息,还可以显示与该Pod相关的最近的Event事件,事件信息对于查错非常有用。

如果某个Pod一直处于Pending状态,我们就可以通过kubectl describe了解具体的原因：

没有可用的Node以供调度，可能原因为pod端口冲突，或者受Taints影响，。
开启了资源配额管理，但在当前调度的目标节点上资源不足。
镜像下载失败等。

查看pod详细信息

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl describe pods   etcd-vms81.liruilongs.github.io -n kube-system
# pod创建的基本信息
Name:                 etcd-vms81.liruilongs.github.io
Namespace:            kube-system
Priority:             2000001000
Priority Class Name:  system-node-critical
Node:                 vms81.liruilongs.github.io/192.168.26.81
Start Time:           Tue, 25 Jan 2022 21:54:20 +0800
Labels:               component=etcd
                      tier=control-plane
Annotations:          kubeadm.kubernetes.io/etcd.advertise-client-urls: https://192.168.26.81:2379
                      kubernetes.io/config.hash: 1502584f9ab841720212d4341d723ba2
                      kubernetes.io/config.mirror: 1502584f9ab841720212d4341d723ba2
                      kubernetes.io/config.seen: 2021-12-13T00:01:04.834825537+08:00
                      kubernetes.io/config.source: file
                      seccomp.security.alpha.kubernetes.io/pod: runtime/default
Status:               Running # Node当前的运行状态, 
IP:                   192.168.26.81
IPs:
  IP:           192.168.26.81
Controlled By:  Node/vms81.liruilongs.github.io
Containers:
  etcd:  # pod的一些基础信息
    Container ID:  docker://20d99a98a4c2590e8726916932790200ba1cf93c48f3c84ca1298ffdcaa4f28a
    Image:         registry.aliyuncs.com/google_containers/etcd:3.5.0-0
    Image ID:      docker-pullable://registry.aliyuncs.com/google_containers/etcd@sha256:9ce33ba33d8e738a5b85ed50b5080ac746deceed4a7496c550927a7a19ca3b6d
    Port:          <none>
    Host Port:     <none>
    Command:  # 容器运行的一些启动参数
      etcd
      --advertise-client-urls=https://192.168.26.81:2379
      --cert-file=/etc/kubernetes/pki/etcd/server.crt
      --client-cert-auth=true
      --data-dir=/var/lib/etcd
      --initial-advertise-peer-urls=https://192.168.26.81:2380
      --initial-cluster=vms81.liruilongs.github.io=https://192.168.26.81:2380
      --key-file=/etc/kubernetes/pki/etcd/server.key
      --listen-client-urls=https://127.0.0.1:2379,https://192.168.26.81:2379
      --listen-metrics-urls=http://127.0.0.1:2381
      --listen-peer-urls=https://192.168.26.81:2380
      --name=vms81.liruilongs.github.io
      --peer-cert-file=/etc/kubernetes/pki/etcd/peer.crt
      --peer-client-cert-auth=true
      --peer-key-file=/etc/kubernetes/pki/etcd/peer.key
      --peer-trusted-ca-file=/etc/kubernetes/pki/etcd/ca.crt
      --snapshot-count=10000
      --trusted-ca-file=/etc/kubernetes/pki/etcd/ca.crt
    State:          Running
      Started:      Tue, 25 Jan 2022 21:54:20 +0800
    Last State:     Terminated
      Reason:       Error
      Exit Code:    255
      Started:      Mon, 24 Jan 2022 08:35:16 +0800
      Finished:     Tue, 25 Jan 2022 21:53:56 +0800
    Ready:          True
    Restart Count:  128
    Requests: # 涉及到的一些资源信息
      cpu:        100m
      memory:     100Mi
    Liveness:     http-get http://127.0.0.1:2381/health delay=10s timeout=15s period=10s #success=1 #failure=8
    Startup:      http-get http://127.0.0.1:2381/health delay=10s timeout=15s period=10s #success=1 #failure=24
    Environment:  <none>
    Mounts:
      /etc/kubernetes/pki/etcd from etcd-certs (rw)
      /var/lib/etcd from etcd-data (rw)
Conditions:    #pod启动以后会做一系列的自检工作:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:     # 映射的宿主机的数据卷信息，这里的定义为宿主机共享
  etcd-certs:
    Type:          HostPath (bare host directory volume)
    Path:          /etc/kubernetes/pki/etcd
    HostPathType:  DirectoryOrCreate
  etcd-data:
    Type:          HostPath (bare host directory volume)
    Path:          /var/lib/etcd
    HostPathType:  DirectoryOrCreate
QoS Class:         Burstable
Node-Selectors:    <none>
Tolerations:       :NoExecute op=Exists
Events:            <none>  
┌──[root@vms81.liruilongs.github.io]-[~]
└─$

查看集群中的Node节点和节点的详细信息

[root@liruilong k8s]# kubectl  get nodes
NAME        STATUS    AGE
127.0.0.1   Ready     2d
[root@liruilong k8s]# kubectl describe node 127.0.0.1
# Node基本信息:名称、标签、创建时间等。
Name:                   127.0.0.1
Role:
Labels:                 beta.kubernetes.io/arch=amd64
                        beta.kubernetes.io/os=linux
                        kubernetes.io/hostname=127.0.0.1
Taints:                 <none>
CreationTimestamp:      Fri, 27 Aug 2021 00:07:09 +0800
Phase:
# Node当前的运行状态, Node启动以后会做一系列的自检工作:
# 比如磁盘是否满了,如果满了就标注OutODisk=True
# 否则继续检查内存是否不足(如果内存不足,就标注MemoryPressure=True)
# 最后一切正常,就设置为Ready状态(Ready=True)
# 该状态表示Node处于健康状态, Master将可以在其上调度新的任务了(如启动Pod)
Conditions:
  Type                  Status  LastHeartbeatTime                       LastTransitionTime                      Reason                          Message
  ----                  ------  -----------------                       ------------------                      ------                          -------
  OutOfDisk             False   Sun, 29 Aug 2021 23:05:53 +0800         Sat, 28 Aug 2021 00:30:35 +0800         KubeletHasSufficientDisk        kubelet has sufficient disk space available
  MemoryPressure        False   Sun, 29 Aug 2021 23:05:53 +0800         Fri, 27 Aug 2021 00:07:09 +0800         KubeletHasSufficientMemory      kubelet has sufficient memory available
  DiskPressure          False   Sun, 29 Aug 2021 23:05:53 +0800         Fri, 27 Aug 2021 00:07:09 +0800         KubeletHasNoDiskPressure        kubelet has no disk pressure
  Ready                 True    Sun, 29 Aug 2021 23:05:53 +0800         Sat, 28 Aug 2021 00:30:35 +0800         KubeletReady                    kubelet is posting ready status
# Node的主机地址与主机名。
Addresses:              127.0.0.1,127.0.0.1,127.0.0.1
# Node上的资源总量:描述Node可用的系统资源,包括CPU、内存数量、最大可调度Pod数量等,注意到目前Kubernetes已经实验性地支持GPU资源分配了(alpha.kubernetes.io/nvidia-gpu=0)
Capacity:
 alpha.kubernetes.io/nvidia-gpu:        0
 cpu:                                   1
 memory:                                1882012Ki
 pods:                                  110
# Node可分配资源量:描述Node当前可用于分配的资源量。
Allocatable:
 alpha.kubernetes.io/nvidia-gpu:        0
 cpu:                                   1
 memory:                                1882012Ki
 pods:                                  110
# 主机系统信息:包括主机的唯一标识UUID, Linux kernel版本号、操作系统类型与版本、Kubernetes版本号、kubelet与kube-proxy的版本号等。  
System Info:
 Machine ID:                    963c2c41b08343f7b063dddac6b2e486
 System UUID:                   EB90EDC4-404C-410B-800F-3C65816C0E2D
 Boot ID:                       4a9349b0-ce4b-4b4a-8766-c5c4256bb80b
 Kernel Version:                3.10.0-1160.15.2.el7.x86_64
 OS Image:                      CentOS Linux 7 (Core)
 Operating System:              linux
 Architecture:                  amd64
 Container Runtime Version:     docker://1.13.1
 Kubelet Version:               v1.5.2
 Kube-Proxy Version:            v1.5.2
ExternalID:                     127.0.0.1
# 当前正在运行的Pod列表概要信息
Non-terminated Pods:            (3 in total)
  Namespace                     Name                    CPU Requests    CPU Limits      Memory Requests Memory Limits
  ---------                     ----                    ------------    ----------      --------------- -------------
  default                       mysql-2cpt9             0 (0%)          0 (0%)          0 (0%)          0 (0%)
  default                       myweb-53r32             0 (0%)          0 (0%)          0 (0%)          0 (0%)
  default                       myweb-609w4             0 (0%)          0 (0%)          0 (0%)          0 (0%)
# 已分配的资源使用概要信息,例如资源申请的最低、最大允许使用量占系统总量的百分比。
Allocated resources:
  (Total limits may be over 100 percent, i.e., overcommitted.
  CPU Requests  CPU Limits      Memory Requests Memory Limits
  ------------  ----------      --------------- -------------
  0 (0%)        0 (0%)          0 (0%)          0 (0%)
# Node相关的Event信息。
Events:
  FirstSeen     LastSeen        Count   From                    SubObjectPath   Type            Reason                  Message
  ---------     --------        -----   ----                    -------------   --------        ------                  -------
  4h            27m             3       {kubelet 127.0.0.1}                     Warning         MissingClusterDNS       kubelet does not have ClusterDNS IP configured and cannot create Pod using "ClusterFirst" policy. pod: "myweb-609w4_default(01d719dd-08b1-11ec-9d6a-00163e1220cb)". Falling back to DNSDefault policy.
  25m           25m             1       {kubelet 127.0.0.1}                     Warning         MissingClusterDNS       kubelet does not have ClusterDNS IP configured and cannot create Pod using "ClusterFirst" policy. pod: "mysql-2cpt9_default(1c9353ba-08d7-11ec-9d6a-00163e1220cb)". Falling back to DNSDefault policy.

查看容器日志

在需要排查容器内部应用程序生成的日志时，我们可以使用kubectl logs <pod_name>命令

这里打印etcd数据库的日志信息,查看日志中异常的相关信息,这里用过过滤error关键字的方法来查看相关的信息

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl logs  etcd-vms81.liruilongs.github.io -n kube-system | grep -i error | head  -5
{"level":"info","ts":"2022-01-25T13:54:33.191Z","caller":"wal/repair.go:96","msg":"repaired","path":"/var/lib/etcd/member/wal/0000000000000014-0000000000185aba.wal","error":"unexpected EOF"}
{"level":"info","ts":"2022-01-25T13:54:33.192Z","caller":"etcdserver/storage.go:109","msg":"repaired WAL","error":"unexpected EOF"}
{"level":"warn","ts":"2022-01-25T13:54:33.884Z","caller":"embed/config_logging.go:169","msg":"rejected connection","remote-addr":"127.0.0.1:53950","server-name":"","error":"EOF"}
{"level":"warn","ts":"2022-01-25T13:54:33.885Z","caller":"embed/config_logging.go:169","msg":"rejected connection","remote-addr":"127.0.0.1:53948","server-name":"","error":"EOF"}
{"level":"warn","ts":"2022-01-28T03:00:37.549Z","caller":"etcdserver/util.go:166","msg":"apply request took too long","took":"628.230855ms","expected-duration":"100ms","prefix":"read-only range ","request":"key:\"/registry/runtimeclasses/\" range_end:\"/registry/runtimeclasses0\" count_only:true ","response":"","error":"context canceled"}
┌──[root@vms81.liruilongs.github.io]-[~]
└─$

查看Kubernetes服务日志

如果在Linux系统上安装Kubernetes,并且使用systemd系统管理Kubernetes服务,那么systemd的journal系统会接管服务程序的输出日志。在这种环境中,可以通过使用systemd status或journalct具来查看系统服务的日志。例如:

查看服务服务启动的相关信息，通过这个，可以定位服务加载的配置文件信息，启动参数配置情况

┌──[root@vms81.liruilongs.github.io]-[~]
└─$systemctl status kubelet.service -l
● kubelet.service - kubelet: The Kubernetes Node Agent
   Loaded: loaded (/usr/lib/systemd/system/kubelet.service; enabled; vendor preset: disabled)
  Drop-In: /usr/lib/systemd/system/kubelet.service.d
           └─10-kubeadm.conf
   Active: active (running) since 二 2022-01-25 21:53:35 CST; 6 days ago
     Docs: https://kubernetes.io/docs/
 Main PID: 1014 (kubelet)
   Memory: 208.2M
   CGroup: /system.slice/kubelet.service
           └─1014 /usr/bin/kubelet --bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf --config=/var/lib/kubelet/config.yaml --network-plugin=cni --pod-infra-container-image=registry.aliyuncs.com/google_containers/pause:3.5

2月 01 17:47:14 vms81.liruilongs.github.io kubelet[1014]: W0201 17:47:14.258523    1014 container.go:586] Failed to update stats for container "/kubepods.slice/kubepods-burstable.slice/kubepods-burstable-pode1b874bfdef201d69db10b200b8f47d5.slice/docker-c20fa960cfebd38172e123a5d87ecd499518bf22381f7aaa62d57131e7eb1aae.scope": unable to determine device info for dir: /var/lib/docker/overlay2/07d7695f2c479fbd0b654016345fcbacd0838276fb57f8291f993ed6799fae8d/diff: stat failed on /var/lib/docker/overlay2/07d7695f2c479fbd0b654016345fcbacd0838276fb57f8291f993ed6799fae8d/diff with error: no such file or directory, continuing to push stats
。。。。。。。。。。

通过 journalct来查看相关的服务日志信息，查看当前用户下的kubelet服务日志中有error关键字的字段的报错问题

┌──[root@vms81.liruilongs.github.io]-[~]
└─$journalctl  -u kubelet.service  | grep -i error | head -2
1月 25 21:53:55 vms81.liruilongs.github.io kubelet[1014]: I0125 21:53:55.865441    1014 docker_service.go:264] "Docker Info" dockerInfo=&{ID:HN3K:C6LG:QGV7:N2CG:VELF:CJ6T:HFR5:EEKH:HLPO:CDEU:GN3E:QAJJ Containers:32 ContainersRunning:11 ContainersPaused:0 ContainersStopped:21 Images:32 Driver:overlay2 DriverStatus:[[Backing Filesystem xfs] [Supports d_type true] [Native Overlay Diff true] [userxattr false]] SystemStatus:[] Plugins:{Volume:[local] Network:[bridge host ipvlan macvlan null overlay] Authorization:[] Log:[awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog]} MemoryLimit:true SwapLimit:true KernelMemory:true KernelMemoryTCP:true CPUCfsPeriod:true CPUCfsQuota:true CPUShares:true CPUSet:true PidsLimit:true IPv4Forwarding:true BridgeNfIptables:true BridgeNfIP6tables:true Debug:false NFd:26 OomKillDisable:true NGoroutines:39 SystemTime:2022-01-25T21:53:55.833509372+08:00 LoggingDriver:json-file CgroupDriver:systemd CgroupVersion:1 NEventsListener:0 KernelVersion:3.10.0-693.el7.x86_64 OperatingSystem:CentOS Linux 7 (Core) OSVersion:7 OSType:linux Architecture:x86_64 IndexServerAddress:https://index.docker.io/v1/ RegistryConfig:0xc000a8f960 NCPU:2 MemTotal:4126896128 GenericResources:[] DockerRootDir:/var/lib/docker HTTPProxy: HTTPSProxy: NoProxy: Name:vms81.liruilongs.github.io Labels:[] ExperimentalBuild:false ServerVersion:20.10.9 ClusterStore: ClusterAdvertise: Runtimes:map[io.containerd.runc.v2:{Path:runc Args:[] Shim:<nil>} io.containerd.runtime.v1.linux:{Path:runc Args:[] Shim:<nil>} runc:{Path:runc Args:[] Shim:<nil>}] DefaultRuntime:runc Swarm:{NodeID: NodeAddr: LocalNodeState:inactive ControlAvailable:false Error: RemoteManagers:[] Nodes:0 Managers:0 Cluster:<nil> Warnings:[]} LiveRestoreEnabled:false Isolation: InitBinary:docker-init ContainerdCommit:{ID:5b46e404f6b9f661a205e28d59c982d3634148f8 Expected:5b46e404f6b9f661a205e28d59c982d3634148f8} RuncCommit:{ID:v1.0.2-0-g52b36a2 Expected:v1.0.2-0-g52b36a2} InitCommit:{ID:de40ad0 Expected:de40ad0} SecurityOptions:[name=seccomp,profile=default] ProductLicense: DefaultAddressPools:[]
1月 25 21:53:56 vms81.liruilongs.github.io kubelet[1014]: E0125 21:53:56.293100    1014 controller.go:144] failed to ensure lease exists, will retry in 200ms, error: Get "https://192.168.26.81:6443/apis/coordination.k8s.io/v1/namespaces/kube-node-lease/leases/vms81.liruilongs.github.io?timeout=10s": dial tcp 192.168.26.81:6443: connect: connection refused
┌──[root@vms81.liruilongs.github.io]-[~]
└─$

如果不使用systemd系统接管Kubernetes服务的标准输出，则也可以通过日志相关的启动参数来指定日志的存放目录。当然，这里的相关启动参数的配置信息需要通过查看pod文件来查看

查看kube-controller-manager的启动参数和认证相关的配置文件

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl describe  pod kube-controller-manager-vms81.liruilongs.github.io -n kube-system | grep -i -A 20  command
    Command:
      kube-controller-manager
      --allocate-node-cidrs=true
      --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
      --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
      --bind-address=127.0.0.1
      --client-ca-file=/etc/kubernetes/pki/ca.crt
      --cluster-cidr=10.244.0.0/16
      --cluster-name=kubernetes
      --cluster-signing-cert-file=/etc/kubernetes/pki/ca.crt
      --cluster-signing-key-file=/etc/kubernetes/pki/ca.key
      --controllers=*,bootstrapsigner,tokencleaner
      --kubeconfig=/etc/kubernetes/controller-manager.conf
      --leader-elect=true
      --port=0
      --requestheader-client-ca-file=/etc/kubernetes/pki/front-proxy-ca.crt
      --root-ca-file=/etc/kubernetes/pki/ca.crt
      --service-account-private-key-file=/etc/kubernetes/pki/sa.key
      --service-cluster-ip-range=10.96.0.0/12
      --use-service-account-credentials=true
    State:          Running

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl describe  pod kube-controller-manager-vms81.liruilongs.github.io -n kube-system | grep  kubeconfig
      --authentication-kubeconfig=/etc/kubernetes/controller-manager.conf
      --authorization-kubeconfig=/etc/kubernetes/controller-manager.conf
      --kubeconfig=/etc/kubernetes/controller-manager.conf
      /etc/kubernetes/controller-manager.conf from kubeconfig (ro)
  kubeconfig:

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl describe  pod kube-controller-manager-vms81.liruilongs.github.io -n kube-system | grep -i -A 20  Volumes
Volumes:
  ca-certs:
    Type:          HostPath (bare host directory volume)
    Path:          /etc/ssl/certs
    HostPathType:  DirectoryOrCreate
  etc-pki:
    Type:          HostPath (bare host directory volume)
    Path:          /etc/pki
    HostPathType:  DirectoryOrCreate
  flexvolume-dir:
    Type:          HostPath (bare host directory volume)
    Path:          /usr/libexec/kubernetes/kubelet-plugins/volume/exec
    HostPathType:  DirectoryOrCreate
  k8s-certs:
    Type:          HostPath (bare host directory volume)
    Path:          /etc/kubernetes/pki
    HostPathType:  DirectoryOrCreate
  kubeconfig:
    Type:          HostPath (bare host directory volume)
    Path:          /etc/kubernetes/controller-manager.conf
    HostPathType:  FileOrCreate
┌──[root@vms81.liruilongs.github.io]-[~]
└─$

Pod资源对象相关的问题,比如无法创建Pod, Pod启动后就停止或者Pod副本无法增加,等等。此时,可以先确定Pod在哪个节点上,然后登录这个节点,从kubelet的日志中查询该Pod的完整日志,然后进行问题排查。

对于与Pod扩容相关或者与RC相关的问题,则很可能在kube-controller-manager及kube-scheduler的日志中找出问题的关键点。

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl logs  kube-scheduler-vms81.liruilongs.github.io
┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl logs  kube-controller-manager-vms81.liruilongs.github.io

kube-proxy经常被我们忽视,因为即使它意外停止, Pod的状态也是正常的,但会导致某些服务访问异常。这些错误通常与每个节点上的kube-proxy服务有着密切的关系。遇到这些问题时,首先要排查kube-proxy服务的日志,同时排查防火墙服务,要特别留意在防火墙中是否有人为添加的可疑规则。

1 2	┌──[root@vms81.liruilongs.github.io]-[~] └─$kubectl logs kube-proxy-tbwz5

常见问题

由于无法下载pause镜像导致Pod一直处于Pending状态

Pod创建成功，但RESTARTS数量持续增加:容器的启动命令不能保持在前台运行。

通过服务名无法访问服务

在Kubernetes集群中应尽量使用服务名访问正在运行的微服务,但有时会访问失败。由于服务涉及服务名的DNS域名解析、kube-proxy组件的负载分发、后端Pod列表的状态等,所以可通过以下几方面排查问题。

1.查看Service的后端Endpoint是否正常

可以通过kubectl get endpoints <service name>命令查看某个服务的后端Endpoint列表,如果列表为空,则可能因为:

┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl get svc
NAME                                TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)                        AGE
kube-dns                            ClusterIP   10.96.0.10       <none>        53/UDP,53/TCP,9153/TCP         50d
liruilong-kube-prometheus-kubelet   ClusterIP   None             <none>        10250/TCP,10255/TCP,4194/TCP   16d
metrics-server                      ClusterIP   10.111.104.173   <none>        443/TCP                        50d
┌──[root@vms81.liruilongs.github.io]-[~]
└─$kubectl get endpoints
NAME                                ENDPOINTS                                                                 AGE
kube-dns                            10.244.88.66:53,10.244.88.67:53,10.244.88.66:53 + 3 more...               50d
liruilong-kube-prometheus-kubelet   192.168.26.81:10250,192.168.26.82:10250,192.168.26.83:10250 + 6 more...   16d
metrics-server                      <none>                                                                    50d
┌──[root@vms81.liruilongs.github.io]-[~]
└─$

Service的Label Selector与Pod的Label不匹配,沒有相关的pod可以提供能力
后端Pod一直没有达到Ready状态(通过kubectl get pods进一步查看Pod的状态)
**Service的targetPort端口号与Pod的containerPort不一致等**。即容器暴露的端口不是SVC暴露的端口，需要使用targetPort来转发

2·查看Service的名称能否被正确解析为ClusterIP地址

可以通过在客户端容器中ping ..svc进行检查,如果能够得到Service的ClusterlP地址,则说明DNS服务能够正确解析Service的名称;如果不能得到Service的ClusterlP地址,则可能是因为Kubernetes集群的DNS服务工作异常。

3·查看kube-proxy的转发规则是否正确

我们可以将kube-proxy服务设置为IPVS或iptables负载分发模式。

对于IPVS负载分发模式,可以通过ipvsadm工具查看Node上的IPVS规则,查看是否正确设置Service ClusterlP的相关规则。
对于iptables负载分发模式,可以通过查看Node上的iptables规则,查看是否正确设置Service ClusterlP的相关规则。

寻求帮助

网站和社区
`Kubernetes`官网中监控、记录和调试相关问题: https://kubernetes.io/docs/tasks/debug-application-cluster/

`Kubernetes`官方论坛: https://discuss.kubernetes.io/(这个需要科学上网)

`GitHub`库关于`Kubernetes`问题列表:https://github.com/kubernetes/kubernetes/issues

`StackOverflow`网站上关于`Kubernetes`的问题讨论：https://stackoverflow.com/questions/tagged/kubernetes

`Kubernetes Slack`聊天群组: https://kubernetes.slack.com/(需要谷歌账号)