Using kubernetes constraints.gatekeeper.sh with telemetry.istio.io

Question

Pulumi · Accepted Answer

Gatekeeper is an open-source project that provides policy enforcement as a webhook for Kubernetes. It allows you to enforce custom policies on your Kubernetes clusters, ensuring that your configurations are compliant with certain rules. These policies are written in a language called Rego, part of the Open Policy Agent (OPA) project.

Istio telemetry, on the other hand, allows you to gather metrics, logs, and trace data from the mesh and send this data to different telemetry backends. It's a part of the Istio service mesh that provides behavioral insights and operational control over the service mesh as a whole.

Integrating `constraints.gatekeeper.sh` with `telemetry.istio.io` involves creating policies (constraints) that ensure any configurations related to Istio comply with your organization's policies. For example, Gatekeeper can ensure that all `ServiceEntry` resources in Istio have a host specified or that your `VirtualServices` have a valid schema.

Below, we will define a Pulumi TypeScript program that:
1. Sets up the Gatekeeper admission controller on a Kubernetes cluster.
2. Applies a constraint to validate the configuration of Istio resources.

First, you install both the Gatekeeper and Istio operators on the cluster, then you define a constraint template which will tell Gatekeeper what to check for in the Istio configurations. After that, you create an actual constraint that applies the rules specified in the template.

Here is how the Pulumi TypeScript code would look:

```typescript
import * as k8s from "@pulumi/kubernetes";

const gatekeeperOperator = new k8s.yaml.ConfigFile("gatekeeper-operator", {
    // Use the yaml.ConfigFile class to install the Gatekeeper operator.
    // The file should contain the necessary resources to install Gatekeeper.
    file: "https://raw.githubusercontent.com/open-policy-agent/gatekeeper/release-3.3/deploy/gatekeeper.yaml",
});

const istioOperator = new k8s.yaml.ConfigFile("istio-operator", {
    // Use the yaml.ConfigFile class to install the Istio operator.
    // The file should contain the necessary resources to install Istio and its telemetry features.
    file: "https://istio.io/operator.yaml",
});

// Make sure to install Gatekeeper and Istio before proceeding with the next steps
const gatekeeperReady = gatekeeperOperator.ready;
const istioReady = istioOperator.ready;

// Once Gatekeeper is installed, you can define a ConstraintTemplate
const constraintTemplate = new k8s.apiextensions.CustomResource("istio-service-entry-constraint-template", {
    apiVersion: "templates.gatekeeper.sh/v1beta1",
    kind: "ConstraintTemplate",
    metadata: {
        name: "k8sserviceentry",
    },
    spec: {
        crd: {
            spec: {
                names: {
                    kind: "K8sServiceEntry",
                },
                validation: {
                    // In openAPIV3Schema, you define what the ServiceEntry must comply with
                    openAPIV3Schema: {
                        properties: {
                            spec: {
                                properties: {
                                    hosts: {
                                        type: "array",
                                        items: { type: "string" },
                                    },
                                },
                                required: ["hosts"],
                            },
                        },
                    },
                },
            },
        },
        targets: [
            {
                target: "admission.k8s.gatekeeper.sh",
                rego: `
                package k8sserviceentry

violation[{"msg": msg, "details": {"missing_hosts": missing_hosts}}] {
                    input.review.object.kind == "ServiceEntry"
                    not input.review.object.spec.hosts
                    missing_hosts := input.review.object.spec.hosts
                    msg := sprintf("ServiceEntry %v has no hosts defined", [input.review.object.metadata.name])
                }`,
            },
        ],
    },
    // Define dependencies to ensure correct order of creation
}, { dependsOn: [gatekeeperReady] });

// Now, you can create an actual constraint using the template you just defined
const serviceEntryConstraint = new k8s.apiextensions.CustomResource("istio-service-entry-constraint", {
    apiVersion: "constraints.gatekeeper.sh/v1beta1",
    kind: "K8sServiceEntry",
    metadata: {
        name: "serviceentry-must-have-hosts",
    },
    spec: {
        match: {
            kinds: [
                {
                    apiGroups: ["networking.istio.io"],
                    kinds: ["ServiceEntry"],
                },
            ],
        },
    },
    // Define dependencies to ensure that the constraint is not created before the template
}, { dependsOn: [constraintTemplate] });

export const gatekeeperOperatorStatus = gatekeeperOperator.ready;
export const istioOperatorStatus = istioOperator.ready;
export const serviceEntryConstraintStatus = serviceEntryConstraint.status;
```

In this program:
- We install Gatekeeper and Istio operators using the `k8s.yaml.ConfigFile` class which allows us to apply raw YAML files to the cluster.
- Before creating Gatekeeper constraints, we ensure that the Gatekeeper and Istio operators are ready.
- We define a `ConstraintTemplate` that will validate `ServiceEntry` resources specific to Istio to see if they have a `hosts` field defined, which is a common requirement.
- The `ConstraintTemplate` contains a small snippet of Rego code (`rego:`) which defines what a violation looks like. In this case, if a `ServiceEntry` has no `hosts` field, it’s a violation.
- After defining the template, we create an actual `K8sServiceEntry` constraint that uses this template to enforce the policy on all `ServiceEntry` resources created in the cluster.
- Finally, we export the statuses of the installations and constraint to provide some outputs when the Pulumi program runs.

This code sets the foundation for using Gatekeeper to enforce policies on Istio configurations. You can expand upon this by defining more sophisticated policies addressing various aspects of the Istio service mesh.