aenguerrand / kubernetes-policy-controller

kubernetes-policy-controller

kubernetes-policy-controller

Kubernetes allows decoupling complex logic such as policy decisions from the inner working of the API Server by means of "admission controllers”. Admission control is custom logic executed by a webhook. kubernetes-policy-controller is a mutating and a validating webhook that gets called for matching Kubernetes API server requests by the admission controller. It uses Open Policy Agent (OPA), a policy engine for Cloud Native environments hosted by CNCF as a sandbox-level project.

Status

This is a new project and is in alpha state.

Using kubernetes-policy-controller

1. Deployment

Access to a Kubernetes cluster with "cluster-admin" permission is the only prerequisite.

Deploy kubernetes-policy-controller:

./deploy/deploy-all.sh

Deploy sample policies:

./deploy/deploy-admission-policy.sh

scenarios

There are two scenarios of the policy engine namely Validation and Mutation

• Validation: "all resources R in namespace N are taged with annotation A"
• Mutation: "before a resource R in namespace N is created tag it with tag T"

1. validation scenario

Load the policy as a ConfigMap:

kubectl create configmap example --from-file ./policy/admission/ingress-host-fqdn.rego

kubectl create ns qa

The following call should fail with policy:

kubectl -n qa apply -f ~/opa/ingress-bad.yaml

2. mutation scenario

This policy will mutate resources that define an annotation with the key "test-mutation". The resouces will be updated to include the annotation "foo": "bar".

Load the policy as a ConfigMap:

kubectl create configmap example --from-file ./policy/admission/annotate.rego

First create a Deployment:

kubectl run nginx --image nginx

Check that the Deployment was not mutated:

kubectl get deployment nginx -o json | jq '.metadata'

Annotate the Deployment to indicate that it should be mutated:

kubectl annotate deployment nginx test-mutation=true

Check that the Deployment was mutated:

kubectl get deployment nginx -o json | jq '.metadata'

create-policy

policy language

The kubernetes-policy-controller uses OPA as the policy engine. OPA provides a high-level declarative language for authoring policies and simple APIs to answer policy queries. Policy rules are created as a rego files.

package admission

kubernetes-policy-controller defines a special package name admission which is used to logically execute all the rules. So any rule defined should be part of this package.

package admission

deny rule

Each violation of a policy is a deny rule. So all we need to capture is all deny matches in order to validate.
In the policy package any validation rule should be defined as special name called deny. In order to understand the basic idea lets consider a case where we want to create a rule which will block all API server requests i.e fail validation of all requests. The following models a that will always deny event

package admission

deny[{
    "type": "always",
    "resource": {"kind": kind, "namespace": namespace, "name": name},
    "message": "test always violate",
}] {
    true
}

matches[[kind, namespace, name, matched_resource_output]]

When defining a deny rule, you must find Kubernetes resources that match specific criteria, such as Ingress resources in a particular namespace. kubernetes-policy-controller provides the matches functionality by importing data.kubernetes.matches.

import data.kubernetes.matches

Here are some exampples of how matching can be used:

• Find matching Ingress resources

import data.kubernetes.matches

matches[["ingress", namespace, name, matched_ingress]]

• Find matching "ingress" resources in "production" namespace

import data.kubernetes.matches

matches[["ingress", "production", name, matched_ingress]]

• Find matching "ingress" resources in "production" namespace with name "my-ingress"

import data.kubernetes.matches

matches[["ingress", "production", "my-ingress", matched_ingress]]

Here is an example of a policy which validates that Ingress hostnames must be unique across Namespaces. This policy shows how you can express a pair-wise search. In this case, there is a violation if any two ingresses in different namespaces have the same hostname. Note, you can query OPA to determine whether a single Ingress violates the policy (in which case the cost is linear with the # of Ingresses) or you can query for the set of all Ingresses that violate the policy (in which case the cost is (# of Ingresses)^2.). Author : Torrin Sandall

package admission

import data.kubernetes.matches

deny[{
    "id": "ingress-conflict",
    "resource": {"kind": "ingress", "namespace": namespace, "name": name},
    "message": "ingress host conflicts with an existing ingress",
}] {
    matches[["ingress", namespace, name, matched_ingress]]
    matches[["ingress", other_ns, other_name, other_ingress]]
    namespace != other_ns
    other_ingress.spec.rules[_].host == matched_ingress.spec.rules[_].host
}

patch rule

Patch rule allows mutation of objects.

Example patch

package admission

import data.k8s.matches

##############################################################################
#
# Policy : Construct JSON Patch for annotating boject with foo=bar if it is
# annotated with "test-mutation"
#
##############################################################################

patch[{
    "id": "conditional-annotation",
    "resource": {"kind": kind, "namespace": namespace, "name": name},
    "patch":  p,
}] {
    matches[[kind, namespace, name, matched_object]]
    matched_object.metadata.annotations["test-mutation"]
    p = [{"op": "add", "path": "/metadata/annotations/foo", "value": "bar"}]
}

Contributing

This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.microsoft.com.

When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact [email protected] with any additional questions or comments.