Auditing
Kubernetes auditing provides a security-relevant, chronological set of records documenting the sequence of actions in a cluster. The cluster audits the activities generated by users, by applications that use the Kubernetes API, and by the control plane itself.
Auditing allows cluster administrators 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 records begin their lifecycle inside the kube-apiserver component. Each request on each stage of its execution generates an audit event, which is then pre-processed according to a certain policy and written to a backend. The policy determines what’s recorded and the backends persist the records. The current backend implementations include logs files and webhooks.
Each request can be recorded with an associated stage. The defined stages are:
RequestReceived
- The stage for events generated as soon as the audit handler receives the request, and before it is delegated down the handler chain.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
- The response body has been completed and no more bytes will be sent.Panic
- Events generated when a panic occurred.
Note: The configuration of an Audit Event configuration is different from the Event API object.
The audit logging feature increases the memory consumption of the API server because some context required for auditing is stored for each request. Memory consumption depends on the audit logging configuration.
Audit policy
Audit policy defines rules about what events should be recorded and what data they should include. The audit policy object structure is defined in the audit.k8s.io API group. 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 defined 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. This does not apply for non-resource requests.RequestResponse
- log event metadata, request and response bodies. This does not apply for non-resource requests.
You can pass a file with the policy to kube-apiserver
using the --audit-policy-file
flag. If the flag is omitted, no events are logged. Note that the rules
field must be provided in the audit policy file. A policy with no (0) rules is treated as illegal.
Below is an example audit policy file:
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"
You can use a minimal audit policy file to log all requests at the Metadata
level:
# Log all requests at the Metadata level.
apiVersion: audit.k8s.io/v1
kind: Policy
rules:
- level: Metadata
If you’re crafting your own audit profile, you can use the audit profile for Google Container-Optimized OS as a starting point. You can check the configure-helper.sh script, which generates an audit policy file. You can see most of the audit policy file by looking directly at the script.
You can also refer to the Policy configuration reference for details about the fields defined.
Audit backends
Audit backends persist audit events to an external storage. Out of the box, the kube-apiserver provides two backends:
- Log backend, which writes events into the filesystem
- Webhook backend, which sends events to an external HTTP API
In all cases, audit events follow a structure defined by the Kubernetes API in the audit.k8s.io API group.
Note:
In case of patches, request body is a JSON array with patch operations, not a JSON object with an appropriate Kubernetes API object. For example, the following request body is a valid patch request to /apis/batch/v1/namespaces/some-namespace/jobs/some-job-name
:
[
{
"op": "replace",
"path": "/spec/parallelism",
"value": 0
},
{
"op": "remove",
"path": "/spec/template/spec/containers/0/terminationMessagePolicy"
}
]
Log backend
The log backend writes audit events to a file in JSONlines format. You can configure the log audit backend using the following kube-apiserver
flags:
--audit-log-path
specifies the log file path that log backend uses to write audit events. Not specifying this flag disables log backend.-
means standard out--audit-log-maxage
defined the maximum number of days to retain old audit log files--audit-log-maxbackup
defines the maximum number of audit log files to retain--audit-log-maxsize
defines the maximum size in megabytes of the audit log file before it gets rotated
If your cluster’s control plane runs the kube-apiserver as a Pod, remember to mount the hostPath
to the location of the policy file and log file, so that audit records are persisted. For example:
--audit-policy-file=/etc/kubernetes/audit-policy.yaml \
--audit-log-path=/var/log/kubernetes/audit/audit.log
then mount the volumes:
...
volumeMounts:
- mountPath: /etc/kubernetes/audit-policy.yaml
name: audit
readOnly: true
- mountPath: /var/log/kubernetes/audit/
name: audit-log
readOnly: false
and finally configure the hostPath
:
...
volumes:
- name: audit
hostPath:
path: /etc/kubernetes/audit-policy.yaml
type: File
- name: audit-log
hostPath:
path: /var/log/kubernetes/audit/
type: DirectoryOrCreate
Webhook backend
The webhook audit backend sends audit events to a remote web API, which is assumed to be a form of the Kubernetes API, including means of authentication. You can configure a webhook audit backend using the following kube-apiserver flags:
--audit-webhook-config-file
specifies the path to a file with a webhook configuration. The webhook configuration is effectively a specialized kubeconfig.--audit-webhook-initial-backoff
specifies the amount of time to wait after the first failed request before retrying. Subsequent requests are retried with exponential backoff.
The webhook config file uses the kubeconfig format to specify the remote address of the service and credentials used to connect to it.
Event batching
Both log and webhook backends support batching. Using webhook as an example, here’s the list of available flags. To get the same flag for log backend, replace webhook
with log
in the flag name. By default, batching is enabled in webhook
and disabled in log
. Similarly, by default throttling is enabled in webhook
and disabled in log
.
--audit-webhook-mode
defines the buffering strategy. One of the following:batch
- buffer events and asynchronously process them in batches. This is the default.blocking
- block API server responses on processing each individual event.blocking-strict
- Same as blocking, but when there is a failure during audit logging at the RequestReceived stage, the whole request to the kube-apiserver fails.
The following flags are used only in the batch
mode:
--audit-webhook-batch-buffer-size
defines the number of events to buffer before batching. If the rate of incoming events overflows the buffer, events are dropped.--audit-webhook-batch-max-size
defines the maximum number of events in one batch.--audit-webhook-batch-max-wait
defines the maximum amount of time to wait before unconditionally batching events in the queue.--audit-webhook-batch-throttle-qps
defines the maximum average number of batches generated per second.--audit-webhook-batch-throttle-burst
defines the maximum number of batches generated at the same moment if the allowed QPS was underutilized previously.
Parameter tuning
Parameters should be set to accommodate the load on the API server.
For example, if kube-apiserver receives 100 requests each second, and each request is audited only on ResponseStarted
and ResponseComplete
stages, you should account for ≅200 audit events being generated each second. Assuming that there are up to 100 events in a batch, you should set throttling level at least 2 queries per second. Assuming that the backend can take up to 5 seconds to write events, you should set the buffer size to hold up to 5 seconds of events; that is: 10 batches, or 1000 events.
In most cases however, the default parameters should be sufficient and you don’t have to worry about setting them manually. You can look at the following Prometheus metrics exposed by kube-apiserver and in the logs to monitor the state of the auditing subsystem.
apiserver_audit_event_total
metric contains the total number of audit events exported.apiserver_audit_error_total
metric contains the total number of events dropped due to an error during exporting.
Log entry truncation
Both log and webhook backends support limiting the size of events that are logged. As an example, the following is the list of flags available for the log backend:
audit-log-truncate-enabled
whether event and batch truncating is enabled.audit-log-truncate-max-batch-size
maximum size in bytes of the batch sent to the underlying backend.audit-log-truncate-max-event-size
maximum size in bytes of the audit event sent to the underlying backend.
By default truncate is disabled in both webhook
and log
, a cluster administrator should set audit-log-truncate-enabled
or audit-webhook-truncate-enabled
to enable the feature.
What’s next
- Learn about Mutating webhook auditing annotations.
- Learn more about Event and the Policy resource types by reading the Audit configuration reference.
Last modified April 26, 2022 at 12:30 AM PST: Reorg the monitoring task section (#32823) (f26e8eff2)