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Kubernetes Policies

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Pre-requisite: Kubernetes

In this article, we will be discussing Kubernetes policies, a key feature in the Kubernetes platform that allows administrators to enforce rules and restrictions on the use and management of resources within a cluster. We will cover the basics of Kubernetes policies, including their types and how they are implemented and managed, as well as delve into some of the more advanced features and use cases for Kubernetes policies.

Kubernetes Policy

  • Kubernetes Policies are rules and restrictions that are enforced by the Kubernetes platform on the use and management of resources within a cluster. These policies can be used to enforce security, compliance, and resource allocation rules, among others. There are two main types of Kubernetes policies: resource-based policies and identity-based policies.
  • Resource-based Policies are used to enforce rules and restrictions on the use and management of specific resources within a cluster. For example, a resource-based policy might be used to limit the number of CPU or memory resources that a particular pod or deployment can use.
  • Identity-based Policies, on the other hand, are used to enforce rules and restrictions on the actions that a particular user or group of users can perform within a cluster. For example, an identity-based policy might be used to restrict the ability of a user to create or delete certain resources, or to limit the scope of their access to certain parts of the cluster.

Types of Kubernetes Policies

Network Policy

Network policies in Kubernetes allow you to specify how groups of pods are allowed to communicate with each other and other network endpoints. You can use network policies to isolate pods or allow specific inbound or outbound traffic for pods. Network policies are implemented using a controller that creates iptables rules on the nodes in the cluster.

Pod Security Policy

Pod security policies allow you to specify security constraints that apply to a pod’s containers. You can use pod security policies to specify things like allowed capabilities, allowed privileged operations, and required volume types.

Resource Quotas

Resource quotas allow you to limit the number of resources (such as CPU, memory, and storage) that are consumed by pods in a namespace. You can use resource quotas to prevent one set of pods from using all of the resources in a namespace, leaving none for other pods.

Limit Ranges

Limit ranges allow you to specify the minimum and maximum limits for resources (such as CPU and memory) that can be allocated to pods in a namespace. You can use limit ranges to ensure that pods are not allocated more resources than they need, or to prevent a single pod from consuming all of the resources in a namespace.

Implementation and Management of Policy

  • Kubernetes policies are implemented and managed using the Kubernetes API and the kubectl command-line tool. To create and manage policies, administrators can use the Kubernetes API to create policy objects, which are then enforced by the Kubernetes platform.
  • To create a policy, administrators can use the kubectl create policy command, specifying the type of policy (either resource-based or identity-based), the resources or identities that the policy applies to, and the rules and restrictions that should be enforced.

Here is an example of implementing a Kubernetes policy using the Go programming language:

Go




package main
  
import (
    "context"
    "fmt"
  
    "k8s.io/api/policy/v1beta1"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
)
  
func createPolicy(client *kubernetes.Clientset, policyName string, namespace string) error {
    policy := &v1beta1.PodSecurityPolicy{
        ObjectMeta: metav1.ObjectMeta{
            Name:      policyName,
            Namespace: namespace,
        },
        Spec: v1beta1.PodSecurityPolicySpec{
            Privileged: false,
            SELinux: v1beta1.SELinuxStrategyOptions{
                Rule: v1beta1.SELinuxStrategyRunAsAny,
            },
            SupplementalGroups: v1beta1.SupplementalGroupsStrategyOptions{
                Rule: v1beta1.SupplementalGroupsStrategyMustRunAs,
                Ranges: []v1beta1.IDRange{
                    {
                        Min: 1,
                        Max: 65535,
                    },
                },
            },
            RunAsUser: v1beta1.RunAsUserStrategyOptions{
                Rule: v1beta1.RunAsUserStrategyMustRunAsNonRoot,
            },
            FSGroup: v1beta1.FSGroupStrategyOptions{
                Rule: v1beta1.FSGroupStrategyMustRunAs,
                Ranges: []v1beta1.IDRange{
                    {
                        Min: 1,
                        Max: 65535,
                    },
                },
            },
            Volumes: []v1beta1.FSType{
                "*",
            },
            AllowedCapabilities: []v1beta1.Capability{},
            DefaultAddCapabilities: []v1beta1.Capability{},
            RequiredDropCapabilities: []v1beta1.Capability{
                "ALL",
            },
            HostNetwork: false,
            HostIPC:     false,
            HostPID:     false,
            HostPorts: []v1beta1.HostPortRange{
                {
                    Min: 0,
                    Max: 65535,
                },
            },
        },


To Create a Resource-based policy that limits the number of CPU resources

$ kubectl create policy cpu-limit --type=resource 
--resource=deployment --limit=1

To View existing policies

$ kubectl get policy

Use Cases for Kubernetes Policies

  • Administrators can use policies to enforce rules and restrictions on the use of specific namespaces or labels within a cluster
  • To Create Custom Policy types using the Kubernetes API.
  • Policies can also be used in conjunction with other features of the Kubernetes platform, such as role-based access control (RBAC) and network policies
  • To create more fine-grained controls over the use and management of resources within a cluster.

Conclusion

In this article, we have discussed the basics of Kubernetes policies and how they are used to enforce rules and restrictions on the use and management of resources within a cluster. We have also explored some of the advanced features and use cases for Kubernetes policies, including the ability to create custom policy types and use policies in conjunction with other features of the Kubernetes platform.



Last Updated : 30 Mar, 2023
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