在Kubernetes中，pod是最小的调度单元。当Pod无法在所分配的节点上正常运行时，它可能会被驱逐(evicted)。这种情况可能是由多种原因引起，比如节点资源不足、Pod超出了所分配的资源限制、镜像拉取失败等。

驱逐原因

• 节点资源不足：节点资源包括CPU、内存、存储空间等。当节点资源不足以满足Pod的资源需求时，调度器会选择其中一个或多个Pod驱逐出节点。
• 超出资源限制：Pod可以指定资源上线，例如CPU和内存的限制。如果Pod使用的资源超过指定的限制，该Pod可能会被驱逐。
• 镜像拉取失败：如果Pod所需的镜像无法拉取或拉取失败，K8S可能会重试一定次数后将其标记为“evicted”状态。

问题复现

（1）查看K8S中Pod的状态，发现部分pod的STATUS显示“evicted”状态:

（2）使用 kubectl describe 命令查看Pod的状态和事件。

kubectl describe pod <pod-name> -n <namespace-name>

kubectl describe pod knowledge-base-5799896986-zl55n -n asrank

[root@node-1 ~]# kubectl describe pod knowledge-base-5799896986-zl55n -n asrank
Name:           knowledge-base-5799896986-zl55n
Namespace:      asrank
Priority:       0
Node:           node-1/
Start Time:     Fri, 29 Mar 2024 11:12:16 +0800
Labels:         app=knowledge-base
                istio.io/rev=default
                pod-template-hash=5799896986
                security.istio.io/tlsMode=istio
                service.istio.io/canonical-name=knowledge-base
                service.istio.io/canonical-revision=latest
Annotations:    kubectl.kubernetes.io/default-container: knowledge-base
                kubectl.kubernetes.io/default-logs-container: knowledge-base
                prometheus.io/path: /stats/prometheus
                prometheus.io/port: 15020
                prometheus.io/scrape: true
                sidecar.istio.io/status:
                  {"initContainers":["istio-init"],"containers":["istio-proxy"],"volumes":["istio-envoy","istio-data","istio-podinfo","istiod-ca-cert"],"ima...
Status:         Failed
Reason:         Evicted
Message:        The node was low on resource: memory. Container knowledge-base was using 43775192Ki, which exceeds its request of 5000Mi. 
IP:             
IPs:            <none>
Controlled By:  ReplicaSet/knowledge-base-5799896986
Init Containers:
  istio-init:
    Image:      hub.pmlabs.com.cn/sail/istio/proxyv2:1.10.6
    Port:       <none>
    Host Port:  <none>
    Args:
      istio-iptables
      -p
      15001
      -z
      15006
      -u
      1337
      -m
      REDIRECT
      -i
      *
      -x
      
      -b
      *
      -d
      15090,15021,15020
    Limits:
      cpu:     2
      memory:  1Gi
    Requests:
      cpu:        100m
      memory:     128Mi
    Environment:  <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cfzc5 (ro)
Containers:
  knowledge-base:
    Image:      hub.pmlabs.com.cn/asrank/knowledge-base:1.01.201
    Port:       9303/TCP
    Host Port:  0/TCP
    Limits:
      cpu:     24
      memory:  48Gi
    Requests:
      cpu:     1
      memory:  5000Mi
    Environment:
      PROFILE:         prod
      MYSQL_PASSWORD:  <set to the key 'MYSQL_ROOT_PASSWORD' in secret 'mysql-root-password'>  Optional: false
    Mounts:
      /data/ from datasets (rw)
      /etc/localtime from date-config (rw)
      /log/ from app-log (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cfzc5 (ro)
  istio-proxy:
    Image:      hub.pmlabs.com.cn/sail/istio/proxyv2:1.10.6
    Port:       15090/TCP
    Host Port:  0/TCP
    Args:
      proxy
      sidecar
      --domain
      $(POD_NAMESPACE).svc.cluster.local
      --serviceCluster
      knowledge-base.$(POD_NAMESPACE)
      --proxyLogLevel=warning
      --proxyComponentLogLevel=misc:error
      --log_output_level=default:info
      --concurrency
      2
    Limits:
      cpu:     2
      memory:  1Gi
    Requests:
      cpu:      100m
      memory:   128Mi
    Readiness:  http-get http://:15021/healthz/ready delay=1s timeout=3s period=2s #success=1 #failure=30
    Environment:
      JWT_POLICY:                    first-party-jwt
      PILOT_CERT_PROVIDER:           istiod
      CA_ADDR:                       istiod.istio-system.svc:15012
      POD_NAME:                      knowledge-base-5799896986-zl55n (v1:metadata.name)
      POD_NAMESPACE:                 asrank (v1:metadata.namespace)
      INSTANCE_IP:                    (v1:status.podIP)
      SERVICE_ACCOUNT:                (v1:spec.serviceAccountName)
      HOST_IP:                        (v1:status.hostIP)
      CANONICAL_SERVICE:              (v1:metadata.labels['service.istio.io/canonical-name'])
      CANONICAL_REVISION:             (v1:metadata.labels['service.istio.io/canonical-revision'])
      PROXY_CONFIG:                  {}
                                     
      ISTIO_META_POD_PORTS:          [
                                         {"containerPort":9303,"protocol":"TCP"}
                                     ]
      ISTIO_META_APP_CONTAINERS:     knowledge-base
      ISTIO_META_CLUSTER_ID:         Kubernetes
      ISTIO_META_INTERCEPTION_MODE:  REDIRECT
      ISTIO_META_WORKLOAD_NAME:      knowledge-base
      ISTIO_META_OWNER:              kubernetes://apis/apps/v1/namespaces/asrank/deployments/knowledge-base
      ISTIO_META_MESH_ID:            cluster.local
      TRUST_DOMAIN:                  cluster.local
    Mounts:
      /etc/istio/pod from istio-podinfo (rw)
      /etc/istio/proxy from istio-envoy (rw)
      /var/lib/istio/data from istio-data (rw)
      /var/run/secrets/istio from istiod-ca-cert (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-cfzc5 (ro)
Volumes:
  istio-envoy:
    Type:       EmptyDir (a temporary directory that shares a pod's lifetime)
    Medium:     Memory
    SizeLimit:  <unset>
  istio-data:
    Type:       EmptyDir (a temporary directory that shares a pod's lifetime)
    Medium:     
    SizeLimit:  <unset>
  istio-podinfo:
    Type:  DownwardAPI (a volume populated by information about the pod)
    Items:
      metadata.labels -> labels
      metadata.annotations -> annotations
      limits.cpu -> cpu-limit
      requests.cpu -> cpu-request
  istiod-ca-cert:
    Type:      ConfigMap (a volume populated by a ConfigMap)
    Name:      istio-ca-root-cert
    Optional:  false
  date-config:
    Type:          HostPath (bare host directory volume)
    Path:          /etc/localtime
    HostPathType:  
  datasets:
    Type:          HostPath (bare host directory volume)
    Path:          /var/asrank/knowledge-base/data
    HostPathType:  
  app-log:
    Type:          HostPath (bare host directory volume)
    Path:          /var/log/app/asrank/knowledge-base
    HostPathType:  
  default-token-cfzc5:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-cfzc5
    Optional:    false
QoS Class:       Burstable
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute op=Exists for 2s
                 node.kubernetes.io/unreachable:NoExecute op=Exists for 2s
Events:
  Type     Reason   Age   From     Message
  ----     ------   ----  ----     -------
  Warning  Evicted  59m   kubelet  The node was low on resource: memory. Container knowledge-base was using 43775192Ki, which exceeds its request of 5000Mi.
  Normal   Killing  59m   kubelet  Stopping container knowledge-base
  Normal   Killing  59m   kubelet  Stopping container istio-proxy

在Events事件中可以看到，由于该Pod在运行中所需内存超出deployments中request的内存，导致该Pod的container被killed，Pod变为被驱逐(evicted)状态。

Events:
  Type     Reason   Age   From     Message
  ----     ------   ----  ----     -------
  Warning  Evicted  59m   kubelet  The node was low on resource: memory. Container knowledge-base was using 43775192Ki, which exceeds its request of 5000Mi.
  Normal   Killing  59m   kubelet  Stopping container knowledge-base
  Normal   Killing  59m   kubelet  Stopping container istio-proxy

解决方案

1. 分析Pod资源使用情况：检查被驱逐的Pod的资源使用情况，如内存、CPU和磁盘使用率。可以使用kubectl describe pod <pod_name>命令查看Pod的状态和事件。
2. 调整资源限制：根据实际需求调整Pod的资源限制，如增加内存限制或CPU限制。可以在Pod YAML文件中修改资源限制，然后使用kubectl apply -f <pod_yaml_file>命令更新Pod。
3. 扩容节点：如果集群中的所有节点都面临资源不足的情况，可以考虑扩容节点以提供更多资源。可以使用云服务提供商的管理控制台或API扩容节点。
4. 优化应用：优化应用程序以减少资源使用，如减少内存泄漏、优化CPU使用等。
5. 使用优先级和抢占：为Pod设置优先级，以便在资源紧张时根据优先级驱逐Pod。可以在Pod的YAML文件中设置priorityClassName字段。
6. 批量清理

根据上述分析，本次事件是由于资源不足导致的。可以根据实际需求调整Pod的资源限制，在Pod的YAML文件中修改资源限制，然后使用kubectl apply -f <pod_yaml_file>命令更新Pod。

有k9s界面的情况下，也可进行如下操作：
（1）基于k9s，输入 :deployments
（2）选择对应的Pod，按 e 键进入编辑模式
（3）修改 resource 资源信息，使得满足程序运行所需资源大小。如：

	requests:
	  cpu: 10
	  memory: 5Gi
	limits:
	  cpu: 24
	  memory: 48Gi

（4）清理Pod

确认没问题后再做删除被驱逐(evicted)的Pod。

# 查看被驱逐(evicted)的Pod
kubectl get pods -n <namespace-name> |grep  Evicted

# 执行批量删除
kubectl get pods -n <namespace-name> | grep Evicted | awk '{print $1}' | xargs kubectl delete pod -n <namespace-name>