MagTape is a Policy-as-Code tool for Kubernetes that allows for evaluating Kubernetes resources against a set of defined policies to inform and enforce best practice configurations. MagTape includes variable policy enforcement, notifications, and targeted metrics.

MagTape builds on the Kubernetes Admission Webhook concept and uses Open Policy Agent (OPA) for its generic policy language and engine.

Our goal with MagTape is to show an example of wrapping additional business logic and features around OPA's core, not to be a competitor. While MagTape is not primarily meant to be a security tool, it can easily enforce security policy.


MagTape examines kubernetes objects against a set of defined policies (best practice configurations/security concepts) and can deny/alert on objects that fail policy checks. The webhook is written in Python using the Flask framework.


A modern version of Kubernetes with the API enabled. Verify that by the following command:

$ kubectl api-versions | grep

The result should be:

In addition, the MutatingAdmissionWebhook and ValidatingAdmissionWebhook admission controllers should be added and listed in the correct order in the admission-control flag of kube-apiserver.

NOTE: MagTape has been tested and is known to work for Kubernetes versions 1.13+ on various Distros/Cloud Providers (DOKS, GKE, EKS, AKS, PKS, and KinD)


MagTape requires cluster-admin permissions to deploy to Kubernetes since it requires access to create/read/update/delete cluster scoped resources (ValidatingWebhookConfigurations, Events, etc.)

MagTape's default RBAC permissions include get, list, and watch access to Secret resources across all namespaces in the cluster. This is to allow for lookup of user-defined Slack Incoming Webhook URL's. If this feature is not needed. the magtape-read ClusterRole can be adjusted to remove these permissions.


You can use the following command to install MagTape and the example policies from this repo with sane defaults. This won't have all features turned on as they require more configuration up front. Please see the Advanced Install section for more details.

NOTE: The quickstart installation is not meant for production use. Please read through the Advanced Install and Cautions sections, and as always, use your best judgement when configuring MagTape for production scenarios.

NOTE: The master branch of this repository is considered a working branch and may not always be in a functioning state. It's best to select a specific tag for a stable version of MagTape

$ kubectl apply -f

This will do the following

  • Create the magtape-system namespace
  • Create cluster and namespace scoped roles/rolebindings
  • Deploy the MagTape workload and related configs
  • Deploy the example policies from this repo

Once this is complete you can do the following to test

Create and label a test namespace

$ kubectl create ns test1
$ kubectl label ns test1

Deploy some test workloads

# These examples assume you're in the root directory of this repo
# Example with no failures

$ kubectl apply -f ./testing/deployments/test-deploy01.yaml -n test1

# Example with deny
# You should get immediate feedback that this request was denied.

$ kubectl apply -f ./testing/deployments/test-deploy02.yaml -n test1

# Example with failures, but no deny
# While this request won't be denied, a K8s Event will be generated
# and can be viewed with "kubectl get events -n test1"

$ kubectl apply -f ./testing/deployments/test-deploy03.yaml -n test1

Beyond the Basics

Now that you've seen the basics of MagTape, try out some of the other features


Remove all MagTape deployed resources

# Assumes you're in the root directory of this repo
$ kubectl delete -f deploy/install.yaml
$ kubectl delete validatingwebhookconfiguration magtape-webhook


The below policy examples are available within this repo. The can be ignored or custom policies can be added. Policies use OPA's Rego language with a specific format to define policy metadata and the output message. This special formatting is required as it enables the additional functionality of MagTape.

  • Liveness Probe (Check ID: MT1001)
  • Readiness Probe (Check ID: MT1002)
  • Resource Limits (Check ID: MT1003)
  • Resource Requests (Check ID: MT1004)
  • Pod Disruption Budget (Check ID: MT1005)
  • Istio Port Name/Number Mismatch (Check ID: MT1006)
  • Singleton Pods (Check ID: MT1007)
  • Host Port (Check ID: MT1008)
  • emptyDir Volume (Check ID: MT1009)
  • Host Path (Check ID: MT1010)
  • Privileged Pod Security Context (Check ID: MT2001)
  • Node Port Range (Check ID: MT2002)

More detailed info about these policies can be found here.

The policy metadata is defined within each policy similar to this:

policy_metadata = {

    # Set MagTape Policy Info
    "name": "policy-resource-requests",
    "severity": "LOW",
    "errcode": "MT1004",
    "targets": {"Deployment", "StatefulSet", "DaemonSet", "Pod"},

  • name - Defines the name of the specific policy. This should be unique per policy.
  • severity - Defines the severity level of a specific policy. This correlates with the DENY_LEVEL to determine if a policy should result in a deny or not.
  • errcode - A unique code that can be used, typically in reference to an FAQ, to look up additional information about the policy, what produces a failure, and how to resolve failures.
  • targets - This controls which Kubernetes resources the policy targets. Each target should be the singular of the Kubernetes resource as found in the Kind field. Special care should be taken to make sure all target resources maintain similar JSON data paths within the policy logic, or that differences are handled appropriately.

Policies follow normal OPA operations for policy discovery. MagTape provides configuration to OPA to filter which configmaps it targets for discovery. If you're adding your own policies make sure to apply the following labels to the configmap:


Example creating a policy configmap with appropriate labels from an existing Rego file

# Create a policy from a Rego file
$ kubectl create cm my-special-policy -n magtape-system --from-file=my-special-policy.rego --dry-run -o yaml | \
kubectl label --local app=opa -f - --dry-run -o yaml > my-special-policy-cm.yaml

OPA will add/update the annotation on the policy configmaps to show they've been loaded successfully or if there are any syntax/validation issues.

Writing policies that Reference resources outside of the request object

As part of the integration MagTape has with OPA, the kube-mgmt service is also deployed within the MagTape pod. In short, kube-mgmt replicates resources from the Kubernetes cluster into OPA to allow for additional context with policies. kube-mgmt requires permissions to build the resource cache and those permissions should be updated accordingly when policies are developed that expand the scope of resources needed.

Please reference the kube-mgmt documentation on caching for additional information on how to configure kube-mgmt to watch new resource types and adjust the permissions in the magtape-read clusterrole accordingly.

Deny Level

Each policy is assigned a Severity level "LOW", "MED", or "HIGH". This is used to influence what policy checks result in an actual deny, or just become passive (alerting only)

The Deny Level is set within the deployment via an environment variable (MAGTAPE_DENY_VOLUME) and can be set to "OFF", "LOW", "MED", or "HIGH". The Deny Level has an inverse relationship to the Severity of the defined checks, which works as follows:

Deny Level Severities Blocked
OFF None

This configuration provides flexibility around controlling which checks should result in a "deny" and allows for a progressive approach as the platform and its users mature

Health Check

MagTape has a rudimentary healthcheck endpoint configured at /healthz. The endpoint displays a json output including the name of the pod running the webhook, the datetime of the request, and the overall health. This is nothing fancy. If the Flask app is running at all the health will report ok.


MagTape uses a few images for operation. Please reference the image repos for more information on the image structure and contents

K8s Events

K8s Events can be generated for policy failures via the MAGTAPE_K8S_EVENTS_ENABLED environment variable.

Setting this variable to TRUE will cause a Kubernetes event to be created in the target namespace of the request object when a policy failure occurs. This will provide a more native method to passively inform users on policy failures (regardless of whether or not the request is denied).

Slack Alerts

Slack alerts can be enabled and controlled via environment variables (noted above):


Override base domain for Slack Incoming Webhook URL

Some airgapped environments may need to use a forwarder/proxy service to assist in sending alerts to the Slack API. the MAGTAPE_SLACK_WEBHOOK_URL_BASE environment variable allows you to override the base domain for the Slack Incoming Webhook URL to target the forwarding/proxy service. This is very assumptive that the forwarding/proxy service will accept a Slack compliant payload and that the endpoint differs from the default Slack Incoming Webhook URL in domain only (ie. the protocol and trailing paths remain the same).



This configuration will override to be and the outcome will be:

NOTE: The MAGTAPE_SLACK_WEBHOOK_URL_BASE environment variable is optional and if not specified the URL will remain unchanged from what is set in MAGTAPE_SLACK_WEBHOOK_URL_DEFAULT

Default Alert Target

When alerts are enabled they will be sent to the Slack Incoming Webhook URL defined in the MAGTAPE_SLACK_WEBHOOK_URL_DEFAULT environment variable. This is meant to be a channel controlled by the MagTape Webhook administrators.

User-defined Alert Target

When alerts are enabled they can be sent to a user-defined Slack Incoming Webhook URL in addition to the default mentioned above. This can be configured via a Kubernetes Secret resource in a target namespace. The secret should be named magtape-slack and the Slack Incoming Webhook URL should be set as the value (typical base64 encoding) for the webhook-url key. This will allow end-users to receive alerts in their desired Slack Channel for request objects targeting their own namespace.


$ kubectl create secret generic magtape-slack -n my-cool-namespace --from-literal=webhook-url=""

Alert Format

Slack alert examples:



NOTE: For Slack Alerts to work, you will need to configure a Slack Incoming Webhook and set the environment variable for the webhook deployment as noted above.


Prometheus formatted metrics are exposed on the /metrics endpoint. Metrics track counters for requests by:

  • CPU, Memory, and HTTP error rate
  • Number of requests passed, failed, and total
  • Breakdown by namespace
  • Breakdown by policy

Grafana dashboards showing Cluster, Namespace, and Policy scoped metrics are available in the metrics directory. An example Prometheus ServiceMonitor resource is located here.

These dashboards are simple, but serve a few purposes:

  • How busy the MagTape app itself is (ie. should the resources or replica count be increased/decreased)
  • What Namespaces seem to produce the most policy failures (Could indicate the team is struggling with certain concepts, there's something malicious going on, etc.)
  • What policies seem to be the most problematic (Maybe an opportunity to target education/training for specific topics based on the policy scope)

We've found that sometimes thinking about operations from a metrics perspective can lead you to develop a policy that is more about tracking how frequently some action occurs rather than explicitly if it should be allowed or denied. Your mileage may very!


  • Create namespace for testing and label it appropriately

    $ kubectl create ns test1
    $ kubectl label ns test1
  • Deploy test deployment to Kubernetes cluster

    $ kubectl apply -f test-deploy02.yaml -n test1

    NOTE: MagTape should deny this workload and should provide feedback similar to this:

    $ kubectl apply -f test-deploy02.yaml -n test1
    Error from server: error when creating "test-deploy02.yaml": admission webhook "" denied the request: [FAIL] HIGH - Found privileged Security Context for container "test-deploy02" (MT2001), [FAIL] LOW - Liveness Probe missing for container "test-deploy02" (MT1001), [FAIL] LOW - Readiness Probe missing for container "test-deploy02" (MT1002), [FAIL] LOW - Resource limits missing (CPU/MEM) for container "test-deploy02" (MT1003), [FAIL] LOW - Resource requests missing (CPU/MEM) for container "test-deploy02" (MT1004)

Test Samples Available

Info on testing resources can be found in the testing directory

NOTE: These manifests are meant to test deploy-time validation, some pods related to these test manifests may fail to come up properly. A failing pod doesn't represent an issue with MagTape.


Production Considerations

  • By Default the MagTape Validating Webhook Configuration is set to fail "closed". Meaning if the webhook is unreachable or doesn't return an expected response, requests to the Kubernetes API will be blocked. Please adjust the configuration if this is not something that fits your environment.
  • MagTape supports operation with multiple replicas that can increase availability and performance for critical clusters.

Break Glass Scenarios

MagTape can be enabled and disabled on a per namespace basis by utilizing the label on namespace resources. In emergency situations the label can be removed from a namespace to disable policy assessment for workloads in that namespace.

If there are cluster-wide issues you can disable MagTape completely by removing the magtape-webhook Validating Webhook Configuration and deleting the MagTape deployment.


Certificate Trust

The ValidatingWebhookConfiguration needs to have a CA Bundle that includes the CA that signed the TLS cert used to secure the MagTape webhook. If this is not done the required trust between the K8s API and webhook will not exist and the webhook won't function correctly. More info is available here

Access MagTape API from local machine

$ kubectl get pods # to get the name of the running pod
$ kubectl port-forward <pod_name> -n <namespace> 5000:5000

Use Curl to perform HTTP POST to MagTape

$ curl -vX POST https://localhost:5000/ -d @test.json -H "Content-Type: application/json"

Follow logs of the webhook pod

$ kubectl get pods # to get the name of the running pod
$ kubectl logs <pod_name> -n <namespace> -f