This document provides prescriptive guidance for hardening a production installation of a RKE cluster to be used with Rancher v2.5.4. It outlines the configurations and controls required to address Kubernetes benchmark controls from the Center for Information Security (CIS).

This hardening guide describes how to secure the nodes in your cluster, and it is recommended to follow this guide before installing Kubernetes.

This hardening guide is intended to be used for RKE clusters and associated with specific versions of the CIS Kubernetes Benchmark, Kubernetes, and Rancher:

Rancher Version CIS Benchmark Version Kubernetes Version
Rancher v2.5.4 Benchmark 1.6 Kubernetes v1.18

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Overview

This document provides prescriptive guidance for hardening a RKE cluster to be used for installing Rancher v2.5.4 with Kubernetes v1.18 or provisioning a RKE cluster with Kubernetes v1.18 to be used within Rancher v2.5.4. It outlines the configurations required to address Kubernetes benchmark controls from the Center for Information Security (CIS).

For more detail about evaluating a hardened cluster against the official CIS benchmark, refer to the CIS 1.6 Benchmark - Self-Assessment Guide - Rancher v2.5.4.

Known Issues

  • Rancher exec shell and view logs for pods are not functional in a CIS 1.6 hardened setup when only public IP is provided when registering custom nodes. This functionality requires a private IP to be provided when registering the custom nodes.
  • When setting the default_pod_security_policy_template_id: to restricted Rancher creates RoleBindings and ClusterRoleBindings on the default service accounts. The CIS 1.6 5.1.5 check requires the default service accounts have no roles or cluster roles bound to it apart from the defaults. In addition the default service accounts should be configured such that it does not provide a service account token and does not have any explicit rights assignments.

Configure Kernel Runtime Parameters

The following sysctl configuration is recommended for all nodes type in the cluster. Set the following parameters in /etc/sysctl.d/90-kubelet.conf:

vm.overcommit_memory=1
vm.panic_on_oom=0
kernel.panic=10
kernel.panic_on_oops=1
kernel.keys.root_maxbytes=25000000

Run sysctl -p /etc/sysctl.d/90-kubelet.conf to enable the settings.

Configure etcd user and group

A user account and group for the etcd service is required to be setup prior to installing RKE. The uid and gid for the etcd user will be used in the RKE config.yml to set the proper permissions for files and directories during installation time.

create etcd user and group

To create the etcd group run the following console commands.

The commands below use 52034 for uid and gid are for example purposes. Any valid unused uid or gid could also be used in lieu of 52034.

groupadd --gid 52034 etcd
useradd --comment "etcd service account" --uid 52034 --gid 52034 etcd

Update the RKE config.yml with the uid and gid of the etcd user:

services:
  etcd:
    gid: 52034
    uid: 52034

Set automountServiceAccountToken to false for default service accounts

Kubernetes provides a default service account which is used by cluster workloads where no specific service account is assigned to the pod. Where access to the Kubernetes API from a pod is required, a specific service account should be created for that pod, and rights granted to that service account. The default service account should be configured such that it does not provide a service account token and does not have any explicit rights assignments.

For each namespace including default and kube-system on a standard RKE install the default service account must include this value:

automountServiceAccountToken: false

Save the following yaml to a file called account_update.yaml

apiVersion: v1
kind: ServiceAccount
metadata:
  name: default
automountServiceAccountToken: false

Create a bash script file called account_update.sh. Be sure to chmod +x account_update.sh so the script has execute permissions.

#!/bin/bash -e

for namespace in $(kubectl get namespaces -A -o json | jq -r '.items[].metadata.name'); do
  kubectl patch serviceaccount default -n ${namespace} -p "$(cat account_update.yaml)"
done

Ensure that all Namespaces have Network Policies defined

Running different applications on the same Kubernetes cluster creates a risk of one compromised application attacking a neighboring application. Network segmentation is important to ensure that containers can communicate only with those they are supposed to. A network policy is a specification of how selections of pods are allowed to communicate with each other and other network endpoints.

Network Policies are namespace scoped. When a network policy is introduced to a given namespace, all traffic not allowed by the policy is denied. However, if there are no network policies in a namespace all traffic will be allowed into and out of the pods in that namespace. To enforce network policies, a CNI (container network interface) plugin must be enabled. This guide uses canal to provide the policy enforcement. Additional information about CNI providers can be found here

Once a CNI provider is enabled on a cluster a default network policy can be applied. For reference purposes a permissive example is provide below. If you want to allow all traffic to all pods in a namespace (even if policies are added that cause some pods to be treated as “isolated”), you can create a policy that explicitly allows all traffic in that namespace. Save the following yaml as default-allow-all.yaml. Additional documentation about network policies can be found on the Kubernetes site.

This NetworkPolicy is not recommended for production use

---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-allow-all
spec:
  podSelector: {}
  ingress:
  - {}
  egress:
  - {}
  policyTypes:
  - Ingress
  - Egress

Create a bash script file called apply_networkPolicy_to_all_ns.sh. Be sure to chmod +x apply_networkPolicy_to_all_ns.sh so the script has execute permissions.

#!/bin/bash -e

for namespace in $(kubectl get namespaces -A -o json | jq -r '.items[].metadata.name'); do
  kubectl apply -f default-allow-all.yaml -n ${namespace}
done

Execute this script to apply the default-allow-all.yaml the permissive NetworkPolicy to all namespaces.

Reference Hardened RKE cluster.yml configuration

The reference cluster.yml is used by the RKE CLI that provides the configuration needed to achieve a hardened install of Rancher Kubernetes Engine (RKE). Install documentation is provided with additional details about the configuration items. This reference cluster.yml does not include the required nodes directive which will vary depending on your environment. Documentation for node configuration can be found here: https://rancher.com/docs/rke/latest/en/config-options/nodes

# If you intend to deploy Kubernetes in an air-gapped environment,
# please consult the documentation on how to configure custom RKE images.
# https://rancher.com/docs/rke/latest/en/installation/

# the nodes directive is required and will vary depending on your environment
# documentation for node configuration can be found here:
# https://rancher.com/docs/rke/latest/en/config-options/nodes
nodes: []
services:
  etcd:
    image: ""
    extra_args: {}
    extra_binds: []
    extra_env: []
    win_extra_args: {}
    win_extra_binds: []
    win_extra_env: []
    external_urls: []
    ca_cert: ""
    cert: ""
    key: ""
    path: ""
    uid: 52034
    gid: 52034
    snapshot: true
    retention: ""
    creation: ""
    backup_config: null
  kube-api:
    image: ""
    extra_args: {}
    extra_binds: []
    extra_env: []
    win_extra_args: {}
    win_extra_binds: []
    win_extra_env: []
    service_cluster_ip_range: ""
    service_node_port_range: ""
    pod_security_policy: true
    always_pull_images: false
    secrets_encryption_config:
      enabled: true
      custom_config: null
    audit_log:
      enabled: true
      configuration: null
    admission_configuration: null
    event_rate_limit:
      enabled: true
      configuration: null
  kube-controller:
    image: ""
    extra_args:
      feature-gates: RotateKubeletServerCertificate=true
    extra_binds: []
    extra_env: []
    win_extra_args: {}
    win_extra_binds: []
    win_extra_env: []
    cluster_cidr: ""
    service_cluster_ip_range: ""
  scheduler:
    image: ""
    extra_args: {}
    extra_binds: []
    extra_env: []
    win_extra_args: {}
    win_extra_binds: []
    win_extra_env: []
  kubelet:
    image: ""
    extra_args:
      feature-gates: RotateKubeletServerCertificate=true
      protect-kernel-defaults: "true"
      tls-cipher-suites: TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_RSA_WITH_AES_256_GCM_SHA384,TLS_RSA_WITH_AES_128_GCM_SHA256
    extra_binds: []
    extra_env: []
    win_extra_args: {}
    win_extra_binds: []
    win_extra_env: []
    cluster_domain: cluster.local
    infra_container_image: ""
    cluster_dns_server: ""
    fail_swap_on: false
    generate_serving_certificate: true
  kubeproxy:
    image: ""
    extra_args: {}
    extra_binds: []
    extra_env: []
    win_extra_args: {}
    win_extra_binds: []
    win_extra_env: []
network:
  plugin: ""
  options: {}
  mtu: 0
  node_selector: {}
  update_strategy: null
authentication:
  strategy: ""
  sans: []
  webhook: null
addons: |
  apiVersion: policy/v1beta1
  kind: PodSecurityPolicy
  metadata:
    name: restricted
  spec:
    requiredDropCapabilities:
    - NET_RAW
    privileged: false
    allowPrivilegeEscalation: false
    defaultAllowPrivilegeEscalation: false
    fsGroup:
      rule: RunAsAny
    runAsUser:
      rule: MustRunAsNonRoot
    seLinux:
      rule: RunAsAny
    supplementalGroups:
      rule: RunAsAny
    volumes:
    - emptyDir
    - secret
    - persistentVolumeClaim
    - downwardAPI
    - configMap
    - projected
  ---
  apiVersion: networking.k8s.io/v1
  kind: NetworkPolicy
  metadata:
    name: default-allow-all
  spec:
    podSelector: {}
    ingress:
    - {}
    egress:
    - {}
    policyTypes:
    - Ingress
    - Egress
  ---
  apiVersion: v1
  kind: ServiceAccount
  metadata:
    name: default
  automountServiceAccountToken: false
addons_include: []
system_images:
  etcd: ""
  alpine: ""
  nginx_proxy: ""
  cert_downloader: ""
  kubernetes_services_sidecar: ""
  kubedns: ""
  dnsmasq: ""
  kubedns_sidecar: ""
  kubedns_autoscaler: ""
  coredns: ""
  coredns_autoscaler: ""
  nodelocal: ""
  kubernetes: ""
  flannel: ""
  flannel_cni: ""
  calico_node: ""
  calico_cni: ""
  calico_controllers: ""
  calico_ctl: ""
  calico_flexvol: ""
  canal_node: ""
  canal_cni: ""
  canal_controllers: ""
  canal_flannel: ""
  canal_flexvol: ""
  weave_node: ""
  weave_cni: ""
  pod_infra_container: ""
  ingress: ""
  ingress_backend: ""
  metrics_server: ""
  windows_pod_infra_container: ""
ssh_key_path: ""
ssh_cert_path: ""
ssh_agent_auth: false
authorization:
  mode: ""
  options: {}
ignore_docker_version: false
kubernetes_version: v1.18.12-rancher1-1
private_registries: []
ingress:
  provider: ""
  options: {}
  node_selector: {}
  extra_args: {}
  dns_policy: ""
  extra_envs: []
  extra_volumes: []
  extra_volume_mounts: []
  update_strategy: null
  http_port: 0
  https_port: 0
  network_mode: ""
cluster_name:
cloud_provider:
  name: ""
prefix_path: ""
win_prefix_path: ""
addon_job_timeout: 0
bastion_host:
  address: ""
  port: ""
  user: ""
  ssh_key: ""
  ssh_key_path: ""
  ssh_cert: ""
  ssh_cert_path: ""
monitoring:
  provider: ""
  options: {}
  node_selector: {}
  update_strategy: null
  replicas: null
restore:
  restore: false
  snapshot_name: ""
dns: null
upgrade_strategy:
  max_unavailable_worker: ""
  max_unavailable_controlplane: ""
  drain: null
  node_drain_input: null

Reference Hardened RKE Template configuration

The reference RKE Template provides the configuration needed to achieve a hardened install of Kubenetes. RKE Templates are used to provision Kubernetes and define Rancher settings. Follow the Rancher documentaion for additional installation and RKE Template details.

# 
# Cluster Config
# 
default_pod_security_policy_template_id: restricted
docker_root_dir: /var/lib/docker
enable_cluster_alerting: false
enable_cluster_monitoring: false
enable_network_policy: true
# 
# Rancher Config
# 
rancher_kubernetes_engine_config:
  addon_job_timeout: 45
  ignore_docker_version: true
  kubernetes_version: v1.18.12-rancher1-1
# 
#   If you are using calico on AWS
# 
#    network:
#      plugin: calico
#      calico_network_provider:
#        cloud_provider: aws
# 
# # To specify flannel interface
# 
#    network:
#      plugin: flannel
#      flannel_network_provider:
#      iface: eth1
# 
# # To specify flannel interface for canal plugin
# 
#    network:
#      plugin: canal
#      canal_network_provider:
#        iface: eth1
# 
  network:
    mtu: 0
    plugin: canal
  rotate_encryption_key: false
# 
#    services:
#      kube-api:
#        service_cluster_ip_range: 10.43.0.0/16
#      kube-controller:
#        cluster_cidr: 10.42.0.0/16
#        service_cluster_ip_range: 10.43.0.0/16
#      kubelet:
#        cluster_domain: cluster.local
#        cluster_dns_server: 10.43.0.10
# 
  services:
    etcd:
      backup_config:
        enabled: false
        interval_hours: 12
        retention: 6
        safe_timestamp: false
      creation: 12h
      extra_args:
        election-timeout: '5000'
        heartbeat-interval: '500'
      gid: 52034
      retention: 72h
      snapshot: false
      uid: 52034
    kube_api:
      always_pull_images: false
      audit_log:
        enabled: true
      event_rate_limit:
        enabled: true
      pod_security_policy: true
      secrets_encryption_config:
        enabled: true
      service_node_port_range: 30000-32767
    kube_controller:
      extra_args:
        feature-gates: RotateKubeletServerCertificate=true
    kubelet:
      extra_args:
        feature-gates: RotateKubeletServerCertificate=true
        protect-kernel-defaults: 'true'
        tls-cipher-suites: >-
          TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,TLS_RSA_WITH_AES_256_GCM_SHA384,TLS_RSA_WITH_AES_128_GCM_SHA256
      fail_swap_on: false
      generate_serving_certificate: true
  ssh_agent_auth: false
  upgrade_strategy:
    max_unavailable_controlplane: '1'
    max_unavailable_worker: 10%
windows_prefered_cluster: false

Hardened Reference Ubuntu 20.04 LTS cloud-config:

The reference cloud-config is generally used in cloud infrastructure environments to allow for configuration management of compute instances. The reference config configures Ubuntu operating system level settings needed before installing kubernetes.

#cloud-config
apt:
  sources:
    docker.list:
      source: deb [arch=amd64] http://download.docker.com/linux/ubuntu $RELEASE stable
      keyid: 9DC858229FC7DD38854AE2D88D81803C0EBFCD88
system_info:
  default_user:
    groups:
    - docker
write_files:
- path: "/etc/apt/preferences.d/docker"
  owner: root:root
  permissions: '0600'
  content: |
    Package: docker-ce
    Pin: version 5:19*
    Pin-Priority: 800
- path: "/etc/sysctl.d/90-kubelet.conf"
  owner: root:root
  permissions: '0644'
  content: |
    vm.overcommit_memory=1
    vm.panic_on_oom=0
    kernel.panic=10
    kernel.panic_on_oops=1
    kernel.keys.root_maxbytes=25000000
package_update: true
packages:
- docker-ce
- docker-ce-cli
- containerd.io
runcmd:
- sysctl -p /etc/sysctl.d/90-kubelet.conf
- groupadd --gid 52034 etcd
- useradd --comment "etcd service account" --uid 52034 --gid 52034 etcd