website/content/en/docs/tasks/federation/set-up-placement-policies-federation.md

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Set up placement policies in Federation	templates/task	135

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This page shows how to enforce policy-based placement decisions over Federated resources using an external policy engine.

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You need to have a running Kubernetes cluster (which is referenced as host cluster). Please see one of the getting started guides for installation instructions for your platform.

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Deploying Federation and configuring an external policy engine

The Federation control plane can be deployed using kubefed init.

After deploying the Federation control plane, you must configure an Admission Controller in the Federation API server that enforces placement decisions received from the external policy engine.

kubectl apply -f scheduling-policy-admission.yaml

Shown below is an example ConfigMap for the Admission Controller:

{{< codenew file="federation/scheduling-policy-admission.yaml" >}}

The ConfigMap contains three files:

• config.yml specifies the location of the SchedulingPolicy Admission Controller config file.
• scheduling-policy-config.yml specifies the location of the kubeconfig file required to contact the external policy engine. This file can also include a retryBackoff value that controls the initial retry backoff delay in milliseconds.
• opa-kubeconfig is a standard kubeconfig containing the URL and credentials needed to contact the external policy engine.

Edit the Federation API server deployment to enable the SchedulingPolicy Admission Controller.

kubectl -n federation-system edit deployment federation-apiserver

Update the Federation API server command line arguments to enable the Admission Controller and mount the ConfigMap into the container. If there's an existing --enable-admission-plugins flag, append ,SchedulingPolicy instead of adding another line.

--enable-admission-plugins=SchedulingPolicy
--admission-control-config-file=/etc/kubernetes/admission/config.yml

Add the following volume to the Federation API server pod:

- name: admission-config
  configMap:
    name: admission

Add the following volume mount the Federation API server apiserver container:

volumeMounts:
- name: admission-config
  mountPath: /etc/kubernetes/admission

Deploying an external policy engine

The Open Policy Agent (OPA) is an open source, general-purpose policy engine that you can use to enforce policy-based placement decisions in the Federation control plane.

Create a Service in the host cluster to contact the external policy engine:

kubectl apply -f policy-engine-service.yaml

Shown below is an example Service for OPA.

{{< codenew file="federation/policy-engine-service.yaml" >}}

Create a Deployment in the host cluster with the Federation control plane:

kubectl apply -f policy-engine-deployment.yaml

Shown below is an example Deployment for OPA.

{{< codenew file="federation/policy-engine-deployment.yaml" >}}

Configuring placement policies via ConfigMaps

The external policy engine will discover placement policies created in the kube-federation-scheduling-policy namespace in the Federation API server.

Create the namespace if it does not already exist:

kubectl --context=federation create namespace kube-federation-scheduling-policy

Configure a sample policy to test the external policy engine:

{{< code file="policy.rego" >}}

Shown below is the command to create the sample policy:

kubectl --context=federation -n kube-federation-scheduling-policy create configmap scheduling-policy --from-file=policy.rego

This sample policy illustrates a few key ideas:

• Placement policies can refer to any field in Federated resources.
• Placement policies can leverage external context (for example, Cluster metadata) to make decisions.
• Administrative policy can be managed centrally.
• Policies can define simple interfaces (such as the requires-pci annotation) to avoid duplicating logic in manifests.

Testing placement policies

Annotate one of the clusters to indicate that it is PCI certified.

kubectl --context=federation annotate clusters cluster-name-1 pci-certified=true

Deploy a Federated ReplicaSet to test the placement policy.

{{< codenew file="federation/replicaset-example-policy.yaml" >}}

Shown below is the command to deploy a ReplicaSet that does match the policy.

kubectl --context=federation create -f replicaset-example-policy.yaml

Inspect the ReplicaSet to confirm the appropriate annotations have been applied:

kubectl --context=federation get rs nginx-pci -o jsonpath='{.metadata.annotations}'

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