container-resources-policy

Container resources policy

This policy is designed to enforce constraints on the resource requirements of Kubernetes containers. It follows a two-step verification process: initially checking whether the container has defined resource requirements, and subsequently ensuring that these resources fall within the permissible range set by the maximum resource requirements configured in the policy settings.

Configuration

Users can configure the policy using the following parameters in YAML format:

# optional
memory:
  defaultRequest: "100M"
  defaultLimit: "500M"
  maxLimit: "4G"
# optional
cpu:
  defaultRequest: 100m
  defaultLimit: 200m
  maxLimit: 500m
# optional
ignoreImages: ["ghcr.io/foo/bar:1.23", "myimage", "otherimages:v1"]

Users can skip the optional parts of the configuration, but an empty configuration is not allowed. Thus, at least one of the configurations, cpu, or memory should be defined including all their sub fields. All CPU and memory configuration should be expressed using the quantity definitions of Kubernetes.

If you would only like to enforce that requests and limits are set (ie, you do not care what they are set to, just that they have been set), you can set ignoreValues to true. This will skip the enforcement of specific values and only enforce that requests and limits are set. Here is an example of how to configure this:

# optional
memory:
  ignoreValues: true
# optional
cpu:
  defaultRequest: 100m
  defaultLimit: 200m
  maxLimit: 500m
# optional
ignoreImages: ["ghcr.io/foo/bar:1.23", "myimage", "otherimages:v1"]

Please note from the above example, that when ignoreValues is set to true, the defaultRequest, defaultLimit, and maxLimit fields, if set, will be ignored. Additionally, ignoreValues default value is false, so it's recommended to only provide it when you want to set it to true.

[!NOTE] The admission request review evaluated by the policy could be mutated by another admission controller, like the LimitRange admission controller. This means that the policy could accept a resource that at first looks invalid, but that is later mutated by another admission controller to be valid. For example, LimitRange will set the default request values if they are not set.

Any container that uses an image that matches an entry in this list will be excluded from enforcement.

The ignoreImages configuration can be used to exclude containers from enforcement. Any container image that matches an entry in the list will be skipped. Prefix-matching can be signified with *. For example: my-image-*. It is recommended that users use the fully-qualified Docker image name (e.g. start with a domain name) in order to avoid unexpectedly exempting images from an untrusted repository.

The policy verifies the consistency of the values provides:

• defaultRequest must be <= maxLimit
• defaultLimit must be <= maxLimit Full example of policy definition:

apiVersion: policies.kubewarden.io/v1
kind: ClusterAdmissionPolicy
metadata:
  name: container-resources-policy
spec:
  policyServer: container-resources-policy
  module: registry://ghcr.io/kubewarden/policies/container-resources:latest
  rules:
  - apiGroups: [""]
    apiVersions: ["v1"]
    resources: ["pods"]
    operations:
    - CREATE
    - UPDATE
  mutating: true
  settings:
    memory:
      defaultRequest: "1G"
      defaultLimit: "1G"
      maxLimit: "4G"
    cpu:
      defaultRequest: 1
      defaultLimit: 1
      maxLimit: 2
    ignoreImages: ["myimage:latest", "registry.k8s.io/pause"]

Behavior

The policy skips all the containers that are using an image that is part of the ignoreImages list. These containers are always considered valid and are never mutated.

When the CPU/Memory request is specified: no action or check is done against it. If the requested memory is higher than the limit the Pod will not be scheduled. This is the same approach taken by the LimitRange admission controller bundled with Kubernetes.

When the CPU/Memory request is not specified: the policy mutates the container definition, the defaultRequest value is used. The policy does not check the consistency of the applied value.

When the CPU/Memory limit is specified: the request is accepted if the limit defined by the container is less than or equal to the maxLimit. Otherwise the request is rejected. In this way the end user becomes aware of the issue and can ask the Kubernetes administrator to add the container image to the ignoreImages list.

When the CPU/Memory limit is not specified: the container is mutated to use the defaultLimit.