This document provides prescriptive guidance for hardening a production installation of a RKE cluster to be used with Rancher v2.5. 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 Benchmark v1.5 Kubernetes 1.15

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Overview

This document provides prescriptive guidance for hardening a RKE cluster to be used for installing Rancher v2.5 with Kubernetes v1.15 or provisioning a RKE cluster with Kubernetes 1.15 to be used within Rancher v2.5. 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 1.5 Benchmark - Self-Assessment Guide - Rancher v2.5.

Known Issues

  • Rancher exec shell and view logs for pods are not functional in a CIS 1.5 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 1.5 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 before 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.
kubernetes_version: "v1.15.9-rancher1-1"
enable_network_policy: true
default_pod_security_policy_template_id: "restricted"
# 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:
    uid: 52034
    gid: 52034
  kube-api:
    pod_security_policy: true
    secrets_encryption_config:
      enabled: true
    audit_log:
      enabled: true
    admission_configuration:
    event_rate_limit:
      enabled: true
  kube-controller:
    extra_args:
      feature-gates: "RotateKubeletServerCertificate=true"
  scheduler:
    image: ""
    extra_args: {}
    extra_binds: []
    extra_env: []
  kubelet:
    generate_serving_certificate: true
    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: []
    cluster_domain: ""
    infra_container_image: ""
    cluster_dns_server: ""
    fail_swap_on: false
  kubeproxy:
    image: ""
    extra_args: {}
    extra_binds: []
    extra_env: []
network:
  plugin: ""
  options: {}
  mtu: 0
  node_selector: {}
authentication:
  strategy: ""
  sans: []
  webhook: null
addons: |
  ---
  apiVersion: v1
  kind: Namespace
  metadata:
    name: ingress-nginx
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: Role
  metadata:
    name: default-psp-role
    namespace: ingress-nginx
  rules:
  - apiGroups:
    - extensions
    resourceNames:
    - default-psp
    resources:
    - podsecuritypolicies
    verbs:
    - use
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: RoleBinding
  metadata:
    name: default-psp-rolebinding
    namespace: ingress-nginx
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: Role
    name: default-psp-role
  subjects:
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: system:serviceaccounts
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: system:authenticated
  ---
  apiVersion: v1
  kind: Namespace
  metadata:
    name: cattle-system
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: Role
  metadata:
    name: default-psp-role
    namespace: cattle-system
  rules:
  - apiGroups:
    - extensions
    resourceNames:
    - default-psp
    resources:
    - podsecuritypolicies
    verbs:
    - use
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: RoleBinding
  metadata:
    name: default-psp-rolebinding
    namespace: cattle-system
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: Role
    name: default-psp-role
  subjects:
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: system:serviceaccounts
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: system:authenticated
  ---
  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: rbac.authorization.k8s.io/v1
  kind: ClusterRole
  metadata:
    name: psp:restricted
  rules:
  - apiGroups:
    - extensions
    resourceNames:
    - restricted
    resources:
    - podsecuritypolicies
    verbs:
    - use
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRoleBinding
  metadata:
    name: psp:restricted
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: ClusterRole
    name: psp:restricted
  subjects:
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: system:serviceaccounts
  - apiGroup: rbac.authorization.k8s.io
    kind: Group
    name: system:authenticated
  ---
  apiVersion: v1
  kind: ServiceAccount
  metadata:
    name: tiller
    namespace: kube-system
  ---
  apiVersion: rbac.authorization.k8s.io/v1
  kind: ClusterRoleBinding
  metadata:
    name: tiller
  roleRef:
    apiGroup: rbac.authorization.k8s.io
    kind: ClusterRole
    name: cluster-admin
  subjects:
  - kind: ServiceAccount
    name: tiller
    namespace: kube-system

addons_include: []
system_images:
  etcd: ""
  alpine: ""
  nginx_proxy: ""
  cert_downloader: ""
  kubernetes_services_sidecar: ""
  kubedns: ""
  dnsmasq: ""
  kubedns_sidecar: ""
  kubedns_autoscaler: ""
  coredns: ""
  coredns_autoscaler: ""
  kubernetes: ""
  flannel: ""
  flannel_cni: ""
  calico_node: ""
  calico_cni: ""
  calico_controllers: ""
  calico_ctl: ""
  calico_flexvol: ""
  canal_node: ""
  canal_cni: ""
  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
private_registries: []
ingress:
  provider: ""
  options: {}
  node_selector: {}
  extra_args: {}
  dns_policy: ""
  extra_envs: []
  extra_volumes: []
  extra_volume_mounts: []
cluster_name: ""
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: {}
restore:
  restore: false
  snapshot_name: ""
dns: 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: 30
  addons: |-
    ---
    apiVersion: v1
    kind: Namespace
    metadata:
      name: ingress-nginx
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: Role
    metadata:
      name: default-psp-role
      namespace: ingress-nginx
    rules:
    - apiGroups:
      - extensions
      resourceNames:
      - default-psp
      resources:
      - podsecuritypolicies
      verbs:
      - use
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: RoleBinding
    metadata:
      name: default-psp-rolebinding
      namespace: ingress-nginx
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: Role
      name: default-psp-role
    subjects:
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:serviceaccounts
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:authenticated
    ---
    apiVersion: v1
    kind: Namespace
    metadata:
      name: cattle-system
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: Role
    metadata:
      name: default-psp-role
      namespace: cattle-system
    rules:
    - apiGroups:
      - extensions
      resourceNames:
      - default-psp
      resources:
      - podsecuritypolicies
      verbs:
      - use
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: RoleBinding
    metadata:
      name: default-psp-rolebinding
      namespace: cattle-system
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: Role
      name: default-psp-role
    subjects:
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:serviceaccounts
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:authenticated
    ---
    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: rbac.authorization.k8s.io/v1
    kind: ClusterRole
    metadata:
      name: psp:restricted
    rules:
    - apiGroups:
      - extensions
      resourceNames:
      - restricted
      resources:
      - podsecuritypolicies
      verbs:
      - use
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: ClusterRoleBinding
    metadata:
      name: psp:restricted
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: psp:restricted
    subjects:
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:serviceaccounts
    - apiGroup: rbac.authorization.k8s.io
      kind: Group
      name: system:authenticated
    ---
    apiVersion: v1
    kind: ServiceAccount
    metadata:
      name: tiller
      namespace: kube-system
    ---
    apiVersion: rbac.authorization.k8s.io/v1
    kind: ClusterRoleBinding
    metadata:
      name: tiller
    roleRef:
      apiGroup: rbac.authorization.k8s.io
      kind: ClusterRole
      name: cluster-admin
    subjects:
    - kind: ServiceAccount
      name: tiller
      namespace: kube-system
  ignore_docker_version: true
  kubernetes_version: v1.15.9-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
#
#    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:
        address: 127.0.0.1
        feature-gates: RotateKubeletServerCertificate=true
        profiling: 'false'
        terminated-pod-gc-threshold: '1000'
    kubelet:
      extra_args:
        anonymous-auth: 'false'
        event-qps: '0'
        feature-gates: RotateKubeletServerCertificate=true
        make-iptables-util-chains: 'true'
        protect-kernel-defaults: 'true'
        streaming-connection-idle-timeout: 1800s
        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
    scheduler:
      extra_args:
        address: 127.0.0.1
        profiling: 'false'
  ssh_agent_auth: false
windows_prefered_cluster: false

Hardened Reference Ubuntu 18.04 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
packages:
  - curl
  - jq
runcmd:
  - sysctl -w vm.overcommit_memory=1
  - sysctl -w kernel.panic=10
  - sysctl -w kernel.panic_on_oops=1
  - curl https://releases.rancher.com/install-docker/18.09.sh | sh
  - usermod -aG docker ubuntu
  - return=1; while [ $return != 0 ]; do sleep 2; docker ps; return=$?; done
  - addgroup --gid 52034 etcd
  - useradd --comment "etcd service account" --uid 52034 --gid 52034 etcd
write_files:
  - path: /etc/sysctl.d/kubelet.conf
    owner: root:root
    permissions: "0644"
    content: |
      vm.overcommit_memory=1
      kernel.panic=10
      kernel.panic_on_oops=1