gatekeeper

Introduction

OPA is an open source policy engine that is commonly used to implement policies in stacks in a standardized and context-aware manner. gatekeeper is used to manage and implement OPA policies, and manage labels of namespaces in ACK cluster For more information about OPA, see Open Policy Agent. The following figure shows the architecture of gatekeeper.

Usage notes

You can use gatekeeper to constrain pod deployments in specified namespaces based on labels. In this example, a Constraint is defined to declare that all pods created in a specified namespace must be labeled with gatekeeper-test-label. For more information about how to use gatekeeper, see Use gatekeeper.

1. Run the following commands to create a test-gatekeeper namespace and add the name=test-gatekeeper label to the namespace:

   kubectl create ns test-gatekeeper
   kubectl label ns test-gatekeeper name=test-gatekeeper

2. Run the following command to create a Constraint template that can be used to define Constraints on pod labels:

   kubectl apply -f - <<EOF
   apiVersion: templates.gatekeeper.sh/v1beta1
   kind: ConstraintTemplate
   metadata:
     name: k8srequiredlabels
   spec:
     crd:
       spec:
         names:
           kind: K8sRequiredLabels
         validation:
           openAPIV3Schema:
             properties:
               labels:
                 type: array
                 items:
                   type: string
     targets:
       - target: admission.k8s.gatekeeper.sh
         rego: |
           package k8srequiredlabels
           violation[{"msg": msg, "details": {"missing_labels": missing}}] {
             provided := {label | input.review.object.metadata.labels[label]}
             required := {label | label := input.parameters.labels[_]}
             missing := required - provided
             count(missing) > 0
             msg := sprintf("you must provide labels: %v", [missing])
           }
   EOF

   It requires about 10 seconds to initialize the Constraint template.
3. Run the following command to create a Constraint from the preceding Constraint template. This Constraint declares that all pods created in a namespace that is added with the name=test-gatekeeper label must be labeled with gatekeeper-test-label.

   kubectl apply -f - <<EOF
   apiVersion: constraints.gatekeeper.sh/v1beta1
   kind: K8sRequiredLabels
   metadata:
     name: pod-must-have-gatekeeper-test-label
   spec:
     match:
       kinds:
         - apiGroups: [""]
           kinds: ["Pod"]
       namespaceSelector:
         matchExpressions:
         - key: name
           operator: In
           values: ["test-gatekeeper"]
     parameters:
       labels: ["gatekeeper-test-label"]
   
   EOF

   It takes about 10 seconds to initialize the Constraint.
4. Check whether the namespace is constrained.
   • Run the following command to create a pod that is not labeled with gatekeeper-test-label in the test-gatekeeper namespace. The test-gatekeeper namespace is added with name=test-gatekeeper.

     kubectl -n test-gatekeeper run test-deny --image=nginx --restart=Never

     Expected output:

     Error from server ([denied by pod-must-have-gatekeeper-test-label] you must provide labels: {"gatekeeper-test-label"}): admission webhook "validation.gatekeeper.sh" denied the request: [denied by pod-must-have-gatekeeper-test-label] you must provide labels: {"gatekeeper-test-label"}

     The test-gatekeeper namespace is added with name=test-gatekeeper. The pod is to be created without the gatekeeper-test-label label. Therefore, the creation fails.

   • Run the following command to create a pod that is labeled with gatekeeper-test-label in the test-gatekeeper namespace. The test-gatekeeper namespace is added with name=test-gatekeeper.

     kubectl -n test-gatekeeper run test-pass -l gatekeeper-test-label=pass --image=nginx --restart=Never

     Expected output:

     pod/test-pass created

     The test-gatekeeper namespace is added with name=test-gatekeeper. The pod is to be created with the gatekeeper-test-label label. Therefore, the creation succeeds.

   • Run the following command to create a pod that is not labeled with name=test-gatekeeper in a namespace that is not subject to the Constraint:

     kubectl -n default run test-deny --image=nginx --restart=Never

     Expected output:

     pod/test-deny created

     The namespace is not subject to the Constraint. Therefore, the creation succeeds. The created pod is added with name=test-gatekeeper

   The preceding steps show that gatekeeper can be used to constrain pod creations in a specific namespace. In this example, the pod to be created in the namespace must be added with the gatekeeper-test-label label.

Release notes

March 2021

August 2020