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KubeLinter

KubeLinter analyzes Kubernetes YAML files and Helm charts and checks them against various best practices, with a focus on production readiness and security.

KubeLinter runs sensible default checks designed to give you useful information about your Kubernetes YAML files and Helm charts. Use it to check early and often for security misconfigurations and DevOps best practices. Some common issues that KubeLinter identifies are running containers as a non-root user, enforcing least privilege, and storing sensitive information only in secrets.

KubeLinter is configurable, so you can enable and disable checks and create your custom checks, depending on the policies you want to follow within your organization. When a lint check fails, KubeLinter also reports recommendations for resolving any potential issues and returns a non-zero exit code.

Warning

KubeLinter is at an early stage of development. There may be breaking changes in the future to the command usage, flags, and configuration file formats. However, we encourage you to use KubeLinter to test your environment YAML files, see what breaks, and contribute to its development.

Installing KubeLinter

Using Go

To install by using Go, run the following command:

GO111MODULE=on go install golang.stackrox.io/kube-linter/cmd/kube-linter

Otherwise, download the latest binary from Releases and add it to your PATH.

Using Homebrew

To install by using Homebrew on macOS, Linux, and Windows Subsystem for Linux (WSL), run the following command:

brew install kube-linter

Using Docker

  1. Get the latest KubeLinter Docker image: 
    docker pull stackrox/kube-linter:0.1.4

    [!NOTE] While we provide the :latest tag for convenience and ease of experimentation, we recommend using a tag corresponding to a specific release when incorporating KubeLinter into your workflows to avoid unexpected breakages. See the Releases page to view available tags.

  2. Add path to a directory containing your yaml files: docker run command: 
    docker run -v /path/to/files/you/want/to/lint:/dir -v /path/to/config.yaml:/etc/config.yaml stackrox/kube-linter lint /dir --config /etc/config.yaml

KubeLinter Github Action

You can also run KubeLinter as a GitHub Action. To use the KubeLinter Github Action, create a kubelint.yml file (or choose custom *.yml file name) in the .github/workflows/ directory and use stackrox/kube-linter-action@v1.

- name: Scan yamls
  id: kube-lint-scan
  uses: stackrox/kube-linter-action@v1
  with:
    directory: yamls
    config: .kube-linter/config.yaml

The KubeLinter Github Action accepts the following inputs:

Parameter Description
directory (Mandatory) A directory path that contains the Kubernetes YAML files or Chart.yaml file.
config (Optional) A path to your custom KubeLinter configuration file.

Building from source

[!NOTE] Before you build, make sure that you have installed Go.

To build KubeLinter from source:

  1. Clone the KubeLinter repository: 
    git clone [email protected]:stackrox/kube-linter.git
  2. Compile the source code: 
    make build
    This command compiles the source code and creates a kube-linter binary file for your platform in the .gobin folder.
  3. Verify that the compiled binary is working: 
    .gobin/kube-linter version
  4. (Optional) Add the generated binary to your path. Run the following command and add the output to your shell profile (~/.bash_profile, ~/.bashrc or ~/.zshenv): 
    echo export PATH='"${PATH}:'"$(pwd)/.gobin"'"'

Verifying KubeLinter images

KubeLinter images are signed by cosign. We recommend verifying the image before using it.

Once you've installed cosign, you can use the KubeLinter public key to verify the KubeLinter image with:

cat kubelinter-cosign.pub
-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEl0HCkCRzYv0qH5QiazoXeXe2qwFX
DmAszeH26g1s3OSsG/focPWkN88wEKQ5eiE95v+Z2snUQPl/mjPdvqpyjA==
-----END PUBLIC KEY-----


cosign verify --key kubelinter-cosign $IMAGE_NAME

KubeLinter also provides cosign keyless signatures.

You can verify the KubeLinter image with:

# NOTE: Keyless signatures are NOT PRODUCTION ready.

COSIGN_EXPERIMENTAL=1 cosign verify $IMAGE_NAME

Usage

** Kubernetes **

  1. Consider the following sample pod specification file pod.yaml:

    apiVersion: v1
kind: Pod
metadata:
  name: security-context-demo
spec:
  securityContext:
    runAsUser: 1000
    runAsGroup: 3000
    fsGroup: 2000
  volumes:
  - name: sec-ctx-vol
    emptyDir: {}
  containers:
  - name: sec-ctx-demo
    image: busybox
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
    command: [ "sh", "-c", "sleep 1h" ]
    volumeMounts:
    - name: sec-ctx-vol
      mountPath: /data/demo
    securityContext:
      allowPrivilegeEscalation: false

    [!NOTE] This sample file has two production readiness issues and one security issue.

    Security issue

    • The container in this pod is not running as a read-only file system, allowing it to write to the root filesystem.

    Production readiness issue

    • The configuration doesn't specify the container's CPU limits, allowing it to consume excessive CPU.
    • The configuration doesn't specify the container's memory limits, allowing it to consume excessive memory.

  2. To lint this file with KubeLinter, run the following command:

    kube-linter lint pod.yaml

  3. KubeLinter runs the default checks and reports errors.

    pod.yaml: (object: <no namespace>/security-context-demo /v1, Kind=Pod) container "sec-ctx-demo" does not have a read-only root file system (check: no-read-only-root-fs, remediation: Set readOnlyRootFilesystem to true in your container's securityContext.)

pod.yaml: (object: <no namespace>/security-context-demo /v1, Kind=Pod) container "sec-ctx-demo" has cpu limit 0 (check: unset-cpu-requirements, remediation: Set your container's CPU requests and limits depending on its requirements. See https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/#requests-and-limits for more details.)

pod.yaml: (object: <no namespace>/security-context-demo /v1, Kind=Pod) container "sec-ctx-demo" has memory limit 0 (check: unset-memory-requirements, remediation: Set your container's memory requests and limits depending on its requirements.    See https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/#requests-and-limits for more details.)

Error: found 3 lint errors

** Helm **

To run KubeLinter on Helm charts, provide a path to the directory which contains the Chart.yaml file. For example, consider running KubeLinter on a sample Helm chart:

  1. Create a new Helm chart: 
    helm create helm-chart-sample
  2. To lint this Helm chart with KubeLinter, run the following command: 
    kube-linter lint helm-chart-sample/
  3. KubeLinter runs the default checks and reports errors. 
    helm-chart-sample/helm-chart-sample/templates/tests/test-connection.yaml: (object: <no namespace>/test-release-helm-chart-sample-test-connection /v1, Kind=Pod) container "wget" does not have a read-only root file system (check: no-read-only-root-fs, remediation: Set readOnlyRootFilesystem to true in your container's securityContext.)

helm-chart-sample/helm-chart-sample/templates/tests/test-connection.yaml: (object: <no namespace>/test-release-helm-chart-sample-test-connection /v1, Kind=Pod) container "wget" is not set to runAsNonRoot (check: run-as-non-root, remediation: Set runAsUser to a non-zero number, and runAsNonRoot to true, in your pod or container securityContext. See https://kubernetes.io/docs/tasks/configure-pod-container/security-context/ for more details.)

helm-chart-sample/helm-chart-sample/templates/tests/test-connection.yaml: (object: <no namespace>/test-release-helm-chart-sample-test-connection /v1, Kind=Pod) container "wget" has cpu request 0 (check: unset-cpu-requirements, remediation: Set your container's CPU requests and limits depending on its requirements. See https://kubernetes.io/docs/concepts/configuration/manage-resources-containers/#requests-and-limits for more details.)

...

Error: found 12 lint errors

For more details about using and configuring KubeLinter, see the Using KubeLinter topic.

Community

To engage with the KubeLinter community, including maintainers and other users, join KubeLinter on Slack .

To contribute, see the contributing guide.

[!ATTENTION] Our code of conduct governs all participation in the KubeLinter community.

License

KubeLinter is licensed under the Apache License 2.0.