Kubernetes 中审计策略--事件处理

阅读原文时间：2023年07月09日阅读：2

一、审计日志的策略

1、日志记录阶段

kube-apiserver 是负责接收及相应用户请求的一个组件，每一个请求都会有几个阶段，每个阶段都有对应的日志，当前支持的阶段有：

RequestReceived - apiserver 在接收到请求后且在将该请求下发之前会生成对应的审计日志。
ResponseStarted - 在响应 header 发送后并在响应 body 发送前生成日志。这个阶段仅为长时间运行的请求生成（例如 watch）。
ResponseComplete - 当响应 body 发送完并且不再发送数据。
Panic - 当有 panic 发生时生成。

也就是说对 apiserver 的每一个请求理论上会有三个阶段的审计日志生成。

2、日志记录级别

当前支持的日志记录级别有：

None - 不记录日志。
Metadata - 只记录 Request 的一些 metadata (例如 user, timestamp, resource, verb 等)，但不记录 Request 或 Response 的body。
Request - 记录 Request 的 metadata 和 body。
RequestResponse - 最全记录方式，会记录所有的 metadata、Request 和 Response 的 body。

3、日志记录策略

在记录日志的时候尽量只记录所需要的信息，不需要的日志尽可能不记录，避免造成系统资源的浪费。

一个请求不要重复记录，每个请求有三个阶段，只记录其中需要的阶段
不要记录所有的资源，不要记录一个资源的所有子资源
系统的请求不需要记录，kubelet、kube-proxy、kube-scheduler、kube-controller-manager 等对 kube-apiserver 的请求不需要记录
对一些认证信息（secerts、configmaps、token 等）的 body 不记录

审计记录最初产生于 kube-apiserver 内部。每个请求在不同执行阶段都会生成审计事件；这些审计事件会根据特定策略被预处理并写入后端。策略确定要记录的内容和用来存储记录的后端。当

你可以使用 --audit-policy-file 标志将包含策略的文件传递给 kube-apiserver。如果不设置该标志，则不记录事件。注意 rules 字段必须在审计策略文件中提供。没有（0）规则的策略将被视为非法配置。

k8s 审计日志的一个示例：

{
"kind": "EventList",
"apiVersion": "audit.k8s.io/v1beta1",
"Items": [
{
"Level": "Request",
"AuditID": "793e7ae2-5ca7-4ad3-a632-19708d2f8265",
"Stage": "RequestReceived",
"RequestURI": "/api/v1/namespaces/default/pods/test-pre-sf-de7cc-0",
"Verb": "get",
"User": {
"Username": "system:unsecured",
"UID": "",
"Groups": [
"system:masters",
"system:authenticated"
],
"Extra": null
},
"ImpersonatedUser": null,
"SourceIPs": [
"192.168.1.11"
],
"UserAgent": "kube-scheduler/v1.12.2 (linux/amd64) kubernetes/73f3294/scheduler",
"ObjectRef": {
"Resource": "pods",
"Namespace": "default",
"Name": "test-pre-sf-de7cc-0",
"UID": "",
"APIGroup": "",
"APIVersion": "v1",
"ResourceVersion": "",
"Subresource": ""
},
"ResponseStatus": null,
"RequestObject": null,
"ResponseObject": null,
"RequestReceivedTimestamp": "2019-01-11T06:51:43.528703Z",
"StageTimestamp": "2019-01-11T06:51:43.528703Z",
"Annotations": null
}
]
}

二、启用审计日志

当前的审计日志支持两种收集方式：保存为日志文件和调用自定义的 webhook，在 v1.13 中还支持动态的 webhook。

1、将审计日志以 json 格式保存到本地文件

apiserver 配置文件的 KUBE_API_ARGS 中需要添加如下参数：

--audit-policy-file=/etc/kubernetes/audit-policy.yaml --audit-log-path=/var/log/kube-audit --audit-log-format=json

日志保存到本地后再通过 fluentd 等其他组件进行收集。
还有其他几个选项可以指定保留审计日志文件的最大天数、文件的最大数量、文件的大小等。

2、将审计日志打到后端指定的 webhook

--audit-policy-file=/etc/kubernetes/audit-policy.yaml --audit-webhook-config-file=/etc/kubernetes/audit-webhook-kubeconfig

webhook 配置文件实际上是一个 kubeconfig，apiserver 会将审计日志发送到指定的 webhook 后，webhook 接收到日志后可以再分发到 kafka 或其他组件进行收集。

audit-webhook-kubeconfig 示例：

apiVersion: v1
clusters:

cluster:
server: http://127.0.0.1:8081/audit/webhook
name: metric
contexts:
context:
cluster: metric
user: ""
name: default-context
current-context: default-context
kind: Config
preferences: {}
users: []

前面提到过，apiserver 的每一个请求会记录三个阶段的审计日志，但是在实际中并不是需要所有的审计日志，官方也说明了启用审计日志会增加 apiserver 对内存的使用量。

audit-policy.yaml 配置示例：

apiVersion: audit.k8s.io/v1 # This is required.
kind: Policy

Don't generate audit events for all requests in RequestReceived stage.

omitStages:

"RequestReceived"
rules:
# Log pod changes at RequestResponse level
level: RequestResponse
resources:
- group: ""
  # Resource "pods" doesn't match requests to any subresource of pods,
  # which is consistent with the RBAC policy.
  resources: ["pods"]
  # Log "pods/log", "pods/status" at Metadata level
level: Metadata
resources:
- group: ""
  resources: ["pods/log", "pods/status"]
Don't log requests to a configmap called "controller-leader"
level: None
resources:
- group: ""
  resources: ["configmaps"]
  resourceNames: ["controller-leader"]
Don't log watch requests by the "system:kube-proxy" on endpoints or services
level: None
users: ["system:kube-proxy"]
verbs: ["watch"]
resources:
- group: "" # core API group
  resources: ["endpoints", "services"]
Don't log authenticated requests to certain non-resource URL paths.
level: None
userGroups: ["system:authenticated"]
nonResourceURLs:
- "/api*" # Wildcard matching.
- "/version"
Log the request body of configmap changes in kube-system.
level: Request
resources:
- group: "" # core API group
  resources: ["configmaps"]
This rule only applies to resources in the "kube-system" namespace.

The empty string "" can be used to select non-namespaced resources.

namespaces: ["kube-system"]

Log configmap and secret changes in all other namespaces at the Metadata level.
level: Metadata
resources:
- group: "" # core API group
  resources: ["secrets", "configmaps"]
Log all other resources in core and extensions at the Request level.
level: Request
resources:
- group: "" # core API group
- group: "extensions" # Version of group should NOT be included.
A catch-all rule to log all other requests at the Metadata level.
level: Metadata
# Long-running requests like watches that fall under this rule will not
# generate an audit event in RequestReceived.
omitStages:
- "RequestReceived"

你可以使用最低限度的审计策略文件在 Metadata 级别记录所有请求：

# 在 Metadata 级别为所有请求生成日志
apiVersion: audit.k8s.io/v1beta1
kind: Policy
rules:

level: Metadata

kubernetes 启用了审计策略

我们可以使用 Webhooks 将审核日志发送到文件或远程 Web API。

在本文中，我们将强制 kube api-server 将审核日志发送到文件。

K8sMeetup

在 Kubernetes 中启用审计策略（对于审计日志文件）

创建审计策略 YAML 文件：前往 Kubernetes 集群，并使用以下规则创建 audit-policy.yaml：

apiVersion: audit.k8s.io/v1
kind: Policy
rules:
# Log the request body of configmap changes in kube-system.

level: Request
resources:
- group: "" # core API group
  resources: ["configmaps"]
  namespaces: ["kube-system"]
Log configmap and secret changes in all other namespaces at the Metadata level.
level: Metadata
resources:
- group: "" # core API group
  resources: ["secrets", "configmaps"]
A catch-all rule to log all other requests at the Metadata level.
level: Metadata
omitStages:
- "RequestReceived"

更新 kube api-server 清单文件：(kubeadm安装方式)

/etc/kubernetes/manifests/kube-apiserver.yaml
apiVersion: v1
kind: Pod
metadata:
annotations:
    kubeadm.kubernetes.io/kube-apiserver.advertise-address.endpoint: 10.150.90.242:6443
creationTimestamp: null
labels:
    component: kube-apiserver
    tier: control-plane
name: kube-apiserver
namespace: kube-system
spec:
containers:
- command:
    - kube-apiserver
    - --advertise-address=10.150.11.111
    - --allow-privileged=true
    - --authorization-mode=Node,RBAC
    - --client-ca-file=/etc/kubernetes/pki/ca.crt
    - --enable-admission-plugins=NodeRestriction
    - --enable-bootstrap-token-auth=true
    - --etcd-cafile=/etc/kubernetes/pki/etcd/ca.crt
    - --etcd-certfile=/etc/kubernetes/pki/apiserver-etcd-client.crt
    - --etcd-keyfile=/etc/kubernetes/pki/apiserver-etcd-client.key
    - --etcd-servers=https://127.0.0.1:2379
    - --kubelet-client-certificate=/etc/kubernetes/pki/apiserver-kubelet-client.crt
    - --kubelet-client-key=/etc/kubernetes/pki/apiserver-kubelet-client.key
    - --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
    - --proxy-client-cert-file=/etc/kubernetes/pki/front-proxy-client.crt
    - --proxy-client-key-file=/etc/kubernetes/pki/front-proxy-client.key
    - --requestheader-allowed-names=front-proxy-client
    - --requestheader-client-ca-file=/etc/kubernetes/pki/front-proxy-ca.crt
    - --requestheader-extra-headers-prefix=X-Remote-Extra-
    - --requestheader-group-headers=X-Remote-Group
    - --requestheader-username-headers=X-Remote-User
    - --secure-port=6443
    - --service-account-key-file=/etc/kubernetes/pki/sa.pub
    - --service-cluster-ip-range=10.96.0.0/12
    - --tls-cert-file=/etc/kubernetes/pki/apiserver.crt
    - --tls-private-key-file=/etc/kubernetes/pki/apiserver.key
    - --audit-policy-file=/etc/kubernetes/audit-policy.yaml
- --audit-log-path=/var/log/kubernetes/audit/audit.log
    image: registry.aliyuncs.com/google_containers/kube-apiserver:v1.20.0
    imagePullPolicy: IfNotPresent
    livenessProbe:
      failureThreshold: 8
      httpGet:
        host: 10.150.90.242
        path: /healthz
        port: 6443
        scheme: HTTPS
      initialDelaySeconds: 15
      timeoutSeconds: 15
    name: kube-apiserver
    resources:
      requests:
        cpu: 250m
    volumeMounts:
    - mountPath: /etc/ssl/certs
      name: ca-certs
      readOnly: true
    - mountPath: /etc/pki
      name: etc-pki
      readOnly: true
    - mountPath: /etc/kubernetes/pki
      name: k8s-certs
      readOnly: true
    - mountPath: /etc/kubernetes/audit-policy.yaml
name: audit
readOnly: true
- mountPath: /var/log/kubernetes/audit/
name: audit-log
readOnly: false
hostNetwork: true
priorityClassName: system-cluster-critical
volumes:
- hostPath:
      path: /etc/ssl/certs
      type: DirectoryOrCreate
    name: ca-certs
- hostPath:
      path: /etc/pki
      type: DirectoryOrCreate
    name: etc-pki
- hostPath:
      path: /etc/kubernetes/pki
      type: DirectoryOrCreate
    name: k8s-certs
- name: audit
hostPath:
path: /etc/kubernetes/audit-policy.yaml
type: File