--- approvers: - soltysh - sttts - ericchiang title: Auditing --- * TOC {:toc} 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? ## Legacy Audit Kubernetes audit is part of [Kube-apiserver][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="" asgroups="" 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 Kubernetes 1.8 has switched to use the advanced structured audit log by default. To fallback to this legacy audit, disable the advanced auditing feature using the `AdvancedAuditing` feature gate on the [kube-apiserver][kube-apiserver]: ``` --feature-gates=AdvancedAuditing=false ``` ### Configuration [Kube-apiserver][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, '-' means standard out. - `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. Kubernetes 1.8 upgrades the advanced audit feature to beta, and some backward incompatible changes have been committed. `AdvancedAuditing` is customizable 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 [authorization layer](/docs/admin/authorization/) instead of the [HTTP verb](/docs/admin/authorization/#determine-the-request-verb). 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 occurred. ### Audit Policy Audit policy is a document defining rules about what events should be recorded. The policy is passed to the [kube-apiserver][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][audit-api]. Some new fields are supported in beta version, like `resourceNames` and `omitStages`. In Kubernetes 1.8 `kind` and `apiVersion` along with `rules` __must__ be provided in the audit policy file. A policy file with 0 rules, or a policy file that doesn't provide a valid `apiVersion` and `kind` value will be treated as illgal. Some example audit policy files: ```yaml apiVersion: audit.k8s.io/v1beta1 #this is required in Kubernetes 1.8 kind: Policy 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 ``` The next audit policy file shows new features introduced in Kubernetes 1.8: ```yaml apiVersion: audit.k8s.io/v1beta1 kind: Policy rules: # Log pod changes at Request level - level: Request resources: - group: "" # Resource "pods" no longer matches requests to any subresource of pods, # This behavior 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"] # A catch-all rule to log all other requests at the Metadata level. # For this rule we use "omitStages" to omit events at "ReqeustReceived" stage. # Events in this stage will not be sent to backend. - level: Metadata omitStages: - "RequestReceived" ``` You can use a minimal audit policy file to log all requests at the `Metadata` level: ```yaml # Log all requests at the Metadata level. apiVersion: audit.k8s.io/v1beta1 kind: Policy rules: - level: Metadata ``` The [audit profile used by GCE][gce-audit-profile] should be used as reference by admins constructing their own audit profiles. ### Audit backends Audit backends implement strategies for emitting events. The [kube-apiserver][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 long 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][audit-api] 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. All generated events defined by `--audit-policy-file` are recorded in structured json format: ``` {"kind":"Event","apiVersion":"audit.k8s.io/v1beta1","metadata":{"creationTimestamp":null},"level":"Metadata","timestamp":"2017-09-05T10:04:55Z","auditID":"77e58433-d345-40ac-b2d8-9866bd355cea","stage":"RequestReceived","requestURI":"/apis/rbac.authorization.k8s.io/v1/namespaces/default/roles","verb":"list","user":{"username":"kubecfg","groups":["system:masters","system:authenticated"]},"sourceIPs":["172.16.116.128"],"objectRef":{"resource":"roles","namespace":"default","apiGroup":"rbac.authorization.k8s.io","apiVersion":"v1"}} {"kind":"Event","apiVersion":"audit.k8s.io/v1beta1","metadata":{"creationTimestamp":null},"level":"Metadata","timestamp":"2017-09-05T10:04:55Z","auditID":"77e58433-d345-40ac-b2d8-9866bd355cea","stage":"ResponseComplete","requestURI":"/apis/rbac.authorization.k8s.io/v1/namespaces/default/roles","verb":"list","user":{"username":"kubecfg","groups":["system:masters","system:authenticated"]},"sourceIPs":["172.16.116.128"],"objectRef":{"resource":"roles","namespace":"default","apiGroup":"rbac.authorization.k8s.io","apiVersion":"v1"},"responseStatus":{"metadata":{},"code":200}} ``` In alpha version, objectRef.apiVersion holds both the api group and version. In beta version these were break out into objectRef.apiGroup and objectRef.apiVersion. Starting from Kubernetes 1.8, structured json format is used for log backend by default. Use the following option to switch log to legacy format: ``` --audit-log-format=legacy ``` With legacy format, events are formatted as follows: ``` 2017-09-05T06:08:19.885328047-04:00 AUDIT: id="c28a95ad-f9dd-47e1-a617-b6dc152db95f" stage="RequestReceived" ip="172.16.116.128" method="list" user="kubecfg" groups="\"system:masters\",\"system:authenticated\"" as="" asgroups="" namespace="default" uri="/apis/rbac.authorization.k8s.io/v1/namespaces/default/roles" response="" 2017-09-05T06:08:19.885328047-04:00 AUDIT: id="c28a95ad-f9dd-47e1-a617-b6dc152db95f" stage="ResponseComplete" ip="172.16.116.128" method="list" user="kubecfg" groups="\"system:masters\",\"system:authenticated\"" as="" asgroups="" namespace="default" uri="/apis/rbac.authorization.k8s.io/v1/namespaces/default/roles" response="200" ``` Logged events omit the request and response bodies. The `Request` and `RequestResponse` levels are equivalent to `Metadata` for legacy format. This legacy format of advanced audit is different from the [Legacy Audit](# Legacy Audit) discussed above, such as changes to the method values and the introduction of a "stage" for each event. #### Webhook backend The audit webhook backend can be used to have [kube-apiserver][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: ```json { "apiVersion": "audit.k8s.io/v1beta1", "items": [ { "auditID": "24f30caf-d7d4-45d5-b7bd-e7af300d7886", "level": "Metadata", "metadata": { "creationTimestamp": null }, "objectRef": { "apiGroup": "rbac.authorization.k8s.io", "apiVersion": "v1", "name": "jane", "namespace": "default", "resource": "roles" }, "requestURI": "/apis/rbac.authorization.k8s.io/v1/namespaces/default/roles/jane", "responseStatus": { "code": 200, "metadata": {} }, "sourceIPs": [ "172.16.116.128" ], "stage": "ResponseComplete", "timestamp": "2017-09-05T10:20:24Z", "user": { "groups": [ "system:masters", "system:authenticated" ], "username": "kubecfg" }, "verb": "get" } ], "kind": "EventList", "metadata": {} } ``` ### Audit-Id Audit-Id is a unique ID for each http request to kube-apiserver. The ID of events will be the same if they were generated from the same request. Starting from Kubernetes 1.8, if an audit event is generated for the request, kube-apiserver will respond with an Audit-Id in the HTTP header. Note that for some special requests like `kubectl exec`, `kubectl attach`, kube-apiserver works like a proxy, no Audit-Id will be returned even if audit events are recorded. ### Log Collector Examples #### Use fluentd to collect and distribute audit events from log file [Fluentd][fluentd] is an open source data collector for unified logging layer. In this example, we will use fluentd to split audit events by different namespaces. Note that this example requries json format output support in Kubernetes 1.8. 1. install [fluentd, fluent-plugin-forest and fluent-plugin-rewrite-tag-filter][fluentd_install_doc] in the kube-apiserver node 1. create a config file for fluentd $ cat < /etc/fluentd/config # fluentd conf runs in the same host with kube-apiserver @type tail # audit log path of kube-apiserver path /var/log/audit pos_file /var/log/audit.pos format json time_key time time_format %Y-%m-%dT%H:%M:%S.%N%z tag audit #https://github.com/fluent/fluent-plugin-rewrite-tag-filter/issues/13 type record_transformer enable_ruby namespace ${record["objectRef"].nil? ? "none":(record["objectRef"]["namespace"].nil? ? "none":record["objectRef"]["namespace"])} # route audit according to namespace element in context @type rewrite_tag_filter rewriterule1 namespace ^(.+) ${tag}.$1 @type record_transformer remove_keys namespace @type forest subtype file remove_prefix audit 1. start fluentd $ fluentd -c /etc/fluentd/config -vv 1. start kube-apiserver with the following options: --audit-policy-file=/etc/kubernetes/audit-policy.yaml --audit-log-path=/var/log/kube-audit --audit-log-format=json 1. check audits for different namespaces in /var/log/audit-*.log #### Use logstash to collect and distribute audit events from webhook backend [Logstash][logstash] is an open source, server-side data processing tool. In this example, we will use logstash to collect audit events from webhook backend, and save events of different users into different files. 1. install [logstash][logstash_install_doc] 1. create config file for logstash $ cat < /etc/logstash/config input{ http{ #TODO, figure out a way to use kubeconfig file to authenticate to logstash #https://www.elastic.co/guide/en/logstash/current/plugins-inputs-http.html#plugins-inputs-http-ssl port=>8888 } } filter{ split{ # Webhook audit backend sends several events together with EventList # split each event here. field=>[items] # We only need event subelement, remove others. remove_field=>[headers, metadata, apiVersion, "@timestamp", kind, "@version", host] } mutate{ rename => {items=>event} } } output{ file{ # Audit events from different users will be saved into different files. path=>"/var/log/kube-audit-%{[event][user][username]}/audit" } } 1. start logstash $ bin/logstash -f /etc/logstash/config --path.settings /etc/logstash/ 1. create a [kubeconfig file](/docs/tasks/access-application-cluster/authenticate-across-clusters-kubeconfig/) for kube-apiserver webhook audit backend $ cat < /etc/kubernetes/audit-webhook-kubeconfig apiVersion: v1 clusters: - cluster: server: http://:8888 name: logstash contexts: - context: cluster: logstash user: "" name: default-context current-context: default-context kind: Config preferences: {} users: [] EOF 1. start kube-apiserver with the following options: --audit-policy-file=/etc/kubernetes/audit-policy.yaml --audit-webhook-config-file=/etc/kubernetes/audit-webhook-kubeconfig 1. check audits in logstash node's directories /var/log/kube-audit-*/audit Note that in addition to file output plugin, logstash has a variety of outputs that let users route data where they want. For example, users can emit audit events to elasticsearch plugin which supports full-text search and analytics. [audit-api]: https://github.com/kubernetes/kubernetes/blob/v1.8.0-beta.1/staging/src/k8s.io/apiserver/pkg/apis/audit/v1beta1/types.go [kube-apiserver]: /docs/admin/kube-apiserver [gce-audit-profile]: https://github.com/kubernetes/kubernetes/blob/v1.8.0-beta.0/cluster/gce/gci/configure-helper.sh#L532 [fluentd]: http://www.fluentd.org/ [fluentd_install_doc]: http://docs.fluentd.org/v0.12/articles/quickstart#step1-installing-fluentd [logstash]: https://www.elastic.co/products/logstash [logstash_install_doc]: https://www.elastic.co/guide/en/logstash/current/installing-logstash.html