Auditing using constraints

Policy Controller constraint objects enable you to enforce policies for your Kubernetes clusters. To help test your policies, you can add an enforcement action to your constraints. You can then view violations in constraint objects and logs.

Types of enforcement actions

There are two enforcement actions: deny and dryrun.

deny is the default enforcement action. It's automatically enabled, even if you don't add an enforcement action in your constraint. Use deny to prevent a given cluster operation from occurring when there's a violation.

dryrun lets you monitor violations of your rules without actively blocking transactions. You can use it to test if your constraints are working as intended, prior to enabling active enforcement using the deny action. Testing constraints this way can prevent disruptions caused by an incorrectly configured constraint.

Adding enforcement actions

You can add enforcementAction: deny or enforcementAction: dryrun to a constraint.

The following example constraint, named audit.yaml, adds the dryrun action.

#audit.yaml
apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sPSPAllowedUsers
metadata:
  name: user-must-be-3333
spec:
  enforcementAction: dryrun
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]
  parameters:
    runAsUser:
      rule: MustRunAs
      ranges:
        - min: 3333
          max: 3333

Create the constraint. For example, apply it using kubectl apply -f:

kubectl apply -f audit.yaml

Viewing audit results

Audited violations are appended to the Constraint objects and are also written to the logs. Violations that the admission controller rejects do not appear in the logs.

Viewing audit results in constraint objects

To see violations of a given constraint, run the following command and view the spec.status fields.

kubectl get constraint-kind constraint-name -o yaml

Example

To see the output of the constraint from audit.yaml, run the following command:

kubectl get K8sPSPAllowedUsers user-must-be-3333 -o yaml

The output you see is similar to the following:

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sPSPAllowedUsers
metadata:
  creationTimestamp: "2020-05-22T01:34:22Z"
  generation: 1
  name: user-must-be-3333
  resourceVersion: "13351707"
  selfLink: /apis/constraints.gatekeeper.sh/v1beta1/k8spspallowedusers/user-must-be-3333
  uid: 5d0b39a8-9bcc-11ea-bb38-42010a80000c
spec:
  enforcementAction: dryrun
  match:
    kinds:
    - apiGroups:
      - ""
      kinds:
      - Pod
  parameters:
    runAsUser:
      ranges:
      - max: 3333
        min: 3333
      rule: MustRunAs
 status:
  auditTimestamp: "2020-05-22T01:39:05Z"
  byPod:
  - enforced: true
    id: gatekeeper-controller-manager-6b665d4c4d-lwnz5
    observedGeneration: 1
 totalViolations: 5
  violations:
  - enforcementAction: dryrun
    kind: Pod
    message: Container git-sync is attempting to run as disallowed user 65533
    name: git-importer-86564db8cb-5r4gs
    namespace: config-management-system
  - enforcementAction: dryrun
    kind: Pod
    message: Container manager is attempting to run as disallowed user 1000
    name: gatekeeper-controller-manager-6b665d4c4d-lwnz5
    namespace: gatekeeper-system
  - enforcementAction: dryrun
    kind: Pod
    message: Container kube-proxy is attempting to run without a required securityContext/runAsUser
    name: kube-proxy-gke-fishy131-default-pool-7369b17c-cckf
    namespace: kube-system
  - enforcementAction: dryrun
    kind: Pod
    message: Container kube-proxy is attempting to run without a required securityContext/runAsUser
    name: kube-proxy-gke-fishy131-default-pool-7369b17c-jnhb
    namespace: kube-system
  - enforcementAction: dryrun
    kind: Pod
    message: Container kube-proxy is attempting to run without a required securityContext/runAsUser
    name: kube-proxy-gke-fishy131-default-pool-7369b17c-xrd8
    namespace: kube-system

Viewing audit results in logs

You can view audit reports in your logs. To learn more about logs, see Viewing Anthos Config Management logs.

To get all Policy Controller logs, run the following command:

kubectl logs -n gatekeeper-system -l gatekeeper.sh/system=yes

The audit results have "process":"audit" in the log lines, so you can pipe the output to another command and filter by these lines. For example, you could use jq, which parses JSON files and allows you to set a filter for a specific log type.

Example audit result from logging:

{
"level":"info",
"ts":1590111401.9769812,
"logger":"controller",
"msg":"Container kube-proxy is attempting to run without a required securityContext/runAsUser",
"process":"audit",
"audit_id":"2020-05-22T01:36:24Z",
"event_type":"violation_audited",
"constraint_kind":"K8sPSPAllowedUsers",
"constraint_name":"user-must-be-3333",
"constraint_namespace":"",
"constraint_action":"dryrun",
"resource_kind":"Pod",
"resource_namespace":"kube-system",
"resource_name":"kube-proxy-gke-fishy131-default-pool-7369b17c-xrd8"
}

What's next