The gator CLI

Feature State: Gatekeeper version v3.11+ (beta)

The gator CLI is a tool for evaluating Gatekeeper ConstraintTemplates and Constraints in a local environment.

Installation

To install gator, you may either download the binary relevant to your system or build it directly from source. On macOS and Linux, you can also install gator using Homebrew.

To build from source:

go get github.com/open-policy-agent/gatekeeper/cmd/gator

Install with Homebrew:

brew install gator

The gator test subcommand

gator test allows users to test a set of Kubernetes objects against a set of Templates and Constraints. The command returns violations when found and communicates success or failure via its exit status. This command will also attempt to expand any resources passed in if a supplied ExpansionTemplate matches these resources.

Note: The gator verify command was first called gator test. These names were changed to better align gator with other projects in the open-policy-agent space.

Usage

Specifying inputs

gator test supports inputs through the --filename and --image flags, and via stdin. The three methods of input can be used in combination or individually. The --filename and --image flags are repeatable.

The --filename flag can specify a single file or a directory. If a file is specified, that file must end in one of the following extensions: .json, .yaml, .yml. Directories will be walked, and any files of extensions other than the aforementioned three will be skipped.

For example, to test a manifest (piped via stdin) against a folder of policies:

cat my-manifest.yaml | gator test --filename=template-and-constraints/

Or you can specify both as flags:

gator test -f=my-manifest.yaml -f=templates-and-constraints/

❗The --image flag is in alpha stage.

The --image flag specifies a content addressable OCI artifact containing policy files. The image(s) will be copied into the local filesystem in a temporary directory, the location of which can be overridden with the --tempdir flag. Only files with the aforementioned extensions will be processed. For information on how to create OCI policy bundles, see the Bundling Policy into OCI Artifacts section.

For example, to test a manifest (piped via stdin) against an OCI Artifact containing policies:

cat my-manifest.yaml | gator test --image=localhost:5000/gator/template-library:v1 \
  --image=localhost:5000/gator/constraints:v1 

Exit Codes

gator test will return a 0 exit status when the objects, Templates, and Constraints are successfully ingested, no errors occur during evaluation, and no violations are found.

An error during evaluation, for example a failure to read a file, will result in a 1 exit status with an error message printed to stderr.

Policy violations will generate a 1 exit status as well, but violation information will be printed to stdout.

Enforcement Actions

While violation data will always be returned when an object is found to be violating a Constraint, the exit status can vary. A constraint with spec.enforcementAction: "" or spec.enforcementAction: deny will produce a 1 exit code, but other enforcement actions like dryrun will not. This is meant to make the exit code of 1 consistent with rejection of the object by Gatekeeper's webhook. A Constraint set to warn would not trigger a rejection in the webhook, but would produce a violation message. The same is true for that constraint when used in gator test.

Output Formatting

gator test supports a --output flag that allows the user to specify a structured data format for the violation data. This information is printed to stdout.

The allowed values are yaml and json, specified like:

gator test --filename=manifests-and-policies/ --output=json

The gator verify subcommand

Writing Test Suites

gator verify organizes tests into three levels: Suites, Tests, and Cases:

• A Suite is a file which defines Tests.
• A Test declares a ConstraintTemplate, a Constraint, and Cases to test the Constraint.
• A Case defines an object to validate and whether the object is expected to pass validation.

Any file paths declared in a Suite are assumed to be relative to the Suite itself. Absolute paths are not allowed. Thus, it is possible to move around a directory containing a Suite, and the files it uses for tests.

Suites

An example Suite file .

To be valid, a Suite file must declare:

kind: Suite
apiVersion: test.gatekeeper.sh/v1alpha1

gator verify silently ignores files which do not declare these. A Suite may declare multiple Tests, each containing different Templates and Constraints. Each Test in a Suite is independent.

Tests

Each Suite contains a list of Tests under the tests field.

A Test compiles a ConstraintTemplate, and instantiates a Constraint for the ConstraintTemplate. It is an error for the Constraint to have a different type than that defined in the ConstraintTemplate spec.crd.spec.names.kind, or for the ConstraintTemplate to not compile.

Cases

Each Test contains a list of Cases under the cases field.

A Case validates an object against a Constraint. The case may specify that the object is expected to pass or fail validation, and may make assertions about the returned violations (if any).

A Case must specify assertions and whether it expects violations. The simplest way to declare this is:

The Case expects at least one violation:

assertions:
- violations: yes

The Case expects no violations:

assertions:
- violations: no

Assertions contain the following fields, acting as conditions for each assertion to check.

• violations is either "yes", "no", or a non-negative integer.
  • If "yes", at least one violation must otherwise match the assertion.
  • If "no", then no violation messages must otherwise match the assertion.
  • If a nonnegative integer, then exactly that many violations must match. Defaults to "yes".
• message matches violations containing the exact string specified. message is case-sensitive. If not specified or explicitly set to empty string, all messages returned by the Constraint are considered matching.

A Case may specify multiple assertions. For example:

  - name: both-disallowed
    object: samples/repo-must-be-openpolicyagent/disallowed_both.yaml
    assertions:
    - violations: 2
    - message: initContainer
      violations: 1
    - message: container
      violations: 1

This Case specifies:

• There are exactly two violations.
• There is exactly one violation containing "initContainer".
• There is exactly one violation containing "container".

It is valid to assert that no violations match a specified message. For example, the below is valid:

- violations: yes
- violations: no
  message: foobar

This Case specifies that there is at least one violation, and no violations contain the string "foobar".

A Case may specify inventory, which is a list of paths to files containing Kubernetes objects to put in data.inventory for testing referential constraints.

inventory:
- samples/data_objects.yaml

More examples of working gator verify suites are available in the gatekeeper-library repository.

Usage

To run a specific suite:

gator verify suite.yaml

To run all suites in the current directory and all child directories recursively

gator verify ./...

To only run tests whose full names contain a match for a regular expression, use the run flag:

gator verify path/to/suites/... --run "disallowed"

Validating Metadata-Based Constraint Templates

gator verify may be used with an AdmissionReview object to test your constraints. This can be helpful to simulate a certain operation (CREATE, UPDATE, DELETE, etc.) or UserInfo metadata. Recall that the input.review.user can be accessed in the Rego code (see Input Review for more guidance). The AdmissionReview object can be specified where you would specify the object under test above:

  - name: both-disallowed
    object: path/to/test_admission_review.yaml
    assertions:
    - violations: 1

Example for testing the UserInfo metadata:

AdmissionReview, ConstraintTemplate, Constraint:

kind: AdmissionReview
apiVersion: admission.k8s.io/v1beta1
request:
  operation: "UPDATE"
  userInfo:
    username: "system:foo"
  object:
    kind: Pod
    labels:
      - app: "bar"
---
kind: ConstraintTemplate
apiVersion: templates.gatekeeper.sh/v1
metadata:
  name: validateuserinfo
spec:
  crd:
    spec:
      names:
        kind: ValidateUserInfo
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8svalidateuserinfo
        violation[{"msg": msg}] {
          username := input.review.userInfo.username
          not startswith(username, "system:")
          msg := sprintf("username is not allowed to perform this operation: %v", [username])
        }
---
kind: ValidateUserInfo
apiVersion: constraints.gatekeeper.sh/v1
metadata:
  name: always-validate

Gator Suite:

apiVersion: test.gatekeeper.sh/v1alpha1
kind: Suite
tests:
- name: userinfo
  template: template.yaml
  constraint: constraint.yaml
  cases:
  - name: system-user
    object: admission-review.yaml
    assertions:
    - violations: no

Note for DELETE operation, the oldObject should be the object being deleted:

kind: AdmissionReview
apiVersion: admission.k8s.io/v1beta1
request:
  operation: "DELETE"
  userInfo:
    username: "system:foo"
  oldObject:
    kind: Pod
    labels:
      - app: "bar"

Note that audit or gator test are different enforcement points and they don't have the AdmissionReview request metadata.

Run gator verify --help for more information.

The gator expand subcommand

gator expand allows users to test the behavior of their Expansion configs. The command accepts a file or directory containing the expansion configs, which should include the resource(s) under test, the ExpansionTemplate(s), and optionally any Mutation CRs. The command will output a manifest containing the expanded resources.

If the mutators or constraints use spec.match.namespaceSelector, the namespace the resource belongs to must be supplied in order to correctly evaluate the match criteria. If a resource is specified for expansion but its non-default namespace is not supplied, the command will exit 1. See the non default namespace example below.

Usage

Similar to gator test, gator expand expects a --filename or --image flag. The flags can be used individually, in combination, and/or repeated.

gator expand --filename="manifest.yaml" –filename="expansion-policy/" 

Or, using an OCI Artifact for the expansion configuration:

gator expand --filename="my-deployment.yaml" --image=localhost:5000/gator/expansion-policy:v1

By default, gator expand will output to stdout, but a –outputfile flag can be specified to write the results to a file.

gator expand --filename="manifest.yaml" –outputfile="results.yaml"

gator expand can output in yaml or json (default is yaml).

gator expand --filename="manifest.yaml" –format="json"

See gator expand –help for more details. gator expand will exit 1 if there is a problem parsing the configs or expanding the resources.

Non default namespace example

This is an example setup where we include a namespace in a manifest.yaml that we plan on passing to gator expand.

apiVersion: expansion.gatekeeper.sh/v1alpha1
kind: ExpansionTemplate
metadata:
  name: expand-deployments
spec:
  applyTo:
  - groups: [ "apps" ]
    kinds: [ "Deployment" ]
    versions: [ "v1" ]
  templateSource: "spec.template"
  generatedGVK:
    kind: "Pod"
    group: ""
    version: "v1"
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  namespace: my-ns
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80
        args:
        - "/bin/sh"
---
apiVersion: mutations.gatekeeper.sh/v1alpha1
kind: Assign
metadata:
  name: always-pull-image
spec:
  applyTo:
  - groups: [ "" ]
    kinds: [ "Pod" ]
    versions: [ "v1" ]
  location: "spec.containers[name: *].imagePullPolicy"
  parameters:
    assign:
      value: "Always"
  match:
    source: "Generated"
    scope: Namespaced
    kinds:
    - apiGroups: [ ]
      kinds: [ ]
    namespaceSelector:
      matchExpressions:
        - key: admission.gatekeeper.sh/ignore
          operator: DoesNotExist
---
# notice this file is providing the non default namespace `my-ns`
apiVersion: v1
kind: Namespace
metadata:
  name: my-ns

Calling gator expand --filename=manifest.yaml will produce the following output:

apiVersion: v1
kind: Pod
metadata:
  labels:
    app: nginx
  name: nginx-deployment-pod
  namespace: my-ns
spec:
  containers:
  - args:
    - /bin/sh
    image: nginx:1.14.2
    imagePullPolicy: Always
    name: nginx
    ports:
    - containerPort: 80

However, not including the namespace definition in the call to gator expand will exit with a status code of 1 and error out with:

error expanding resources: error expanding resource nginx-deployment: failed to mutate resultant resource nginx-deployment-pod: matching for mutator Assign.mutations.gatekeeper.sh /always-pull-image failed for  Pod my-ns nginx-deployment-pod: failed to run Match criteria: namespace selector for namespace-scoped object but missing Namespace

Bundling Policy into OCI Artifacts

It may be useful to bundle policy files into OCI Artifacts for ingestion during CI/CD workflows. The workflow could perform validation on inbound objects using gator test|expand.

A policy bundle can be composed of any arbitrary file structure, which gator will walk recursively. Any files that do not end in json|yaml|yml will be ignored. gator does not enforce any file schema in the artifacts; it only requires that all files of the support extensions describe valid Kubernetes resources.

We recommend using the Oras CLI to create OCI artifacts. For example, to push a bundle containing the 2 local directories constraints and template_library:

oras push localhost:5000/gator/policy-bundle:v1 ./constraints/:application/vnd.oci.image.layer.v1.tar+gzip \
  ./template_library/:application/vnd.oci.image.layer.v1.tar+gzip

This expects that the constraints and template_library directories are at the path that this command is being run from.

Gotchas

Duplicate violation messages

Rego de-duplicates identical violation messages. If you want to be sure that a test returns multiple violations, use a unique message for each violation. Otherwise, if you specify an exact number of violations, the test may fail.

Matching is case-sensitive

Message declarations are case-sensitive. If a test fails, check that the expected message's capitalization exactly matches the one in the template.

Referential constraints and Namespace-scoped resources

Gator cannot determine if a type is Namespace-scoped or not, so it does not assign objects to the default Namespace automatically. Always specify metadata.namespace for Namespace-scoped objects to prevent test failures, or to keep from specifying templates which will fail in a real cluster.

Platform Compatibility

gator is only automatically tested on Linux for each commit. If you want to use gator on other systems, let us know by replying to this issue.

gator verify has been manually tested on Windows and works as of this commit . Continued functionality is not guaranteed.

File paths which include backslashes are not portable, so suites using such paths will not work as intended on Windows.