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Kubernetes Audit provides a security-relevant chronological set of records documenting the sequence of activities that have affected system by individual users, administrators or other components of the system. It allows cluster administrator to answer the following questions:

- what happened?
- when did it happen?
- who initiated it?
- on what did it happen?
- where was it observed?
- from where was it initiated?
- to where was it going?

Audit logs

Kubernetes audit is part of Kube-apiserver logging all requests processed by the server. Each audit log entry contains two lines:

1. The request line containing a unique ID to match the response and request metadata, such as the source IP, requesting user, impersonation information, resource being requested, etc.
2. The response line containing a unique ID matching the request line and the response code.

Example output for admin user listing pods in the default namespace:

2017-03-21T03:57:09.106841886-04:00 AUDIT: id="c939d2a7-1c37-4ef1-b2f7-4ba9b1e43b53" ip="127.0.0.1" method="GET" user="admin" groups="\"system:masters\",\"system:authenticated\"" as="<self>" asgroups="<lookup>" namespace="default" uri="/api/v1/namespaces/default/pods"
2017-03-21T03:57:09.108403639-04:00 AUDIT: id="c939d2a7-1c37-4ef1-b2f7-4ba9b1e43b53" response="200"

Note that this format changes when enabling the AdvancedAuditing feature discussed later in this document.

Configuration

Kube-apiserver provides the following options which are responsible for configuring where and how audit logs are handled:

• audit-log-path - enables the audit log pointing to a file where the requests are being logged to.
• audit-log-maxage - specifies maximum number of days to retain old audit log files based on the timestamp encoded in their filename.
• audit-log-maxbackup - specifies maximum number of old audit log files to retain.
• audit-log-maxsize - specifies maximum size in megabytes of the audit log file before it gets rotated. Defaults to 100MB

If an audit log file already exists, Kubernetes appends new audit logs to that file. Otherwise, Kubernetes creates an audit log file at the location you specified in audit-log-path. If the audit log file exceeds the size you specify in audit-log-maxsize, Kubernetes will rename the current log file by appending the current timestamp on the file name (before the file extension) and create a new audit log file. Kubernetes may delete old log files when creating a new log file; you can configure how many files are retained and how old they can be by specifying the audit-log-maxbackup and audit-log-maxage options.

Advanced audit

Kubernetes 1.7 expands auditing with experimental functionality such as event filtering and a webhook for integration with external systems. The rest of this document covers features that are alpha and may change in backward incompatible ways.

Enable the alpha auditing features using the AdvancedAuditing feature gate on the kube-apiserver:

--feature-gates=AdvancedAuditing=true

AdvancedAuditingis customizeable in two ways. Policy, which determines what's recorded, and backends, which persist records. Backend implementations include logs files and webhooks.

The structure of audit events changes when enabling the AdvancedAuditing feature flag. This includes some cleanups, such as the method reflecting the verb evaluated by the authoriation layer instead of the HTTP verb ("create" instead of "POST"). Also, instead of always generating two events per request, events are recorded with an associated "stage." The known stages are:

• RequestReceived - The stage for events generated as soon as the audit handler receives the request.
• ResponseStarted - Once the response headers are sent, but before the response body is sent. This stage is only generated for long-running requests (e.g. watch).
• ResponseComplete - Once the response body has been completed.
• Panic - Events generated when a panic occured.

Audit Policy

Audit policy is a document defining rules about what events should be recorded. The policy is passed to the kube-apiserver using the --audit-policy-file flag.

--audit-policy-file=/etc/kubernetes/audit-policy.yaml

If AdvancedAuditing is enabled and this flag is omitted, no events are logged.

The policy file holds rules that determine the level of an event. Known audit levels are:

• None - don't log events that match this rule.
• Metadata - log request metadata (requesting user, timestamp, resource, verb, etc.) but not request or response body.
• Request - log event metadata and request body but not response body.
• RequestResponse - log event metadata, request and response bodies.

When an event is processed it's compared against the list of rules in order. The first matching rule sets the audit level of the event. The audit policy is defined by the audit.k8s.io API group.

An example audit policy file:

rules:
  # 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

You can use a minimal audit policy file to log all requests at the Metadata level:

# Log all requests at the Metadata level.
rules:
- level: Metadata

The audit profile used by GCE should be used as reference by admins constructing their own audit profiles.

Audit backends

Audit backends implement strategies for emitting events. The kube-apiserver provides a logging and webhook backend.

Each request to the API server can generate multiple events, one when the request is received, another when the response is sent, and additional events for log running requests (such as watches). The ID of events will be the same if they were generated from the same request.

The event format is defined by the audit.k8s.io API group. The v1alpha1 format of this API can be found here with more details about the exact fields captured.

Log backend

The behavior of the --audit-log-path flag changes when enabling the AdvancedAuditing feature flag. This includes the cleanups discussed above, such as changes to the method values and the introduction of a "stage" for each event. As before, the id field of the log line indicates which events were generated from the same request. Events are formatted as follows:

2017-06-15T21:50:50.259470834Z AUDIT: id="591e9fde-6a98-46f6-b7bc-ec8ef575696d" stage="RequestReceived" ip="10.2.1.3" method="update" user="system:serviceaccount:kube-system:default" groups="\"system:serviceaccounts\",\"system:serviceaccounts:kube-system\",\"system:authenticated\"" as="<self>" asgroups="<lookup>" namespace="kube-system" uri="/api/v1/namespaces/kube-system/endpoints/kube-controller-manager" response="<deferred>"
2017-06-15T21:50:50.259470834Z AUDIT: id="591e9fde-6a98-46f6-b7bc-ec8ef575696d" stage="ResponseComplete" ip="10.2.1.3" method="update" user="system:serviceaccount:kube-system:default" groups="\"system:serviceaccounts\",\"system:serviceaccounts:kube-system\",\"system:authenticated\"" as="<self>" asgroups="<lookup>" namespace="kube-system" uri="/api/v1/namespaces/kube-system/endpoints/kube-controller-manager" response="200"

Logged evens omit the request and response bodies. The Request and RequestResponse levels are equivalent to Metadata for this backend.

Webhook backend

The audit webhook backend can be used to have kube-apiserver send audit events to a remote service. The webhook requires the AdvancedAuditing feature flag and is configured using the following command line flags:

--audit-webhook-config-file=/etc/kubernetes/audit-webhook-kubeconfig
--audit-webhook-mode=batch

audit-webhook-mode controls buffering strategies used by the webhook. Known modes are:

• batch - buffer events and asynchronously send the set of events to the external service.
• blocking - block API server responses on sending each event to the external service.

The webhook config file uses the kubeconfig format to specify the remote address of the service and credentials used to connect to it.

# clusters refers to the remote service.
clusters:
  - name: name-of-remote-audit-service
    cluster:
      certificate-authority: /path/to/ca.pem  # CA for verifying the remote service.
      server: https://audit.example.com/audit # URL of remote service to query. Must use 'https'.

# users refers to the API server's webhook configuration.
users:
  - name: name-of-api-server
    user:
      client-certificate: /path/to/cert.pem # cert for the webhook plugin to use
      client-key: /path/to/key.pem          # key matching the cert

# kubeconfig files require a context. Provide one for the API server.
current-context: webhook
contexts:
- context:
    cluster: name-of-remote-audit-service
    user: name-of-api-sever
  name: webhook

Events are POSTed as a JSON serialized EventList. An example payload:

{
  "kind": "EventList",
  "apiVersion": "audit.k8s.io/v1alpha1",
  "items": [
    {
      "metadata": {
        "creationTimestamp": null
      },
      "level": "Metadata",
      "timestamp": "2017-06-15T23:07:40Z",
      "auditID": "4faf711a-9094-400f-a876-d9188ceda548",
      "stage": "ResponseComplete",
      "requestURI": "/apis/rbac.authorization.k8s.io/v1beta1/namespaces/kube-public/rolebindings/system:controller:bootstrap-signer",
      "verb": "get",
      "user": {
        "username": "system:apiserver",
        "uid": "97a62906-e4d7-4048-8eda-4f0fb6ff8f1e",
        "groups": [
          "system:masters"
        ]
      },
      "sourceIPs": [
        "127.0.0.1"
      ],
      "objectRef": {
        "resource": "rolebindings",
        "namespace": "kube-public",
        "name": "system:controller:bootstrap-signer",
        "apiVersion": "rbac.authorization.k8s.io/v1beta1"
      },
      "responseStatus": {
        "metadata": {},
        "code": 200
      }
    }
  ]
}