eeb376460d
* Fix inconsistent handling of admission plugin list * Adjust hardening doc with the normalized admission plugin list * Add pre-check for admission plugins format change * Ignore checking admission plugins value when variable is not defined
139 lines
6.5 KiB
Markdown
139 lines
6.5 KiB
Markdown
# Cluster Hardening
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If you want to improve the security on your cluster and make it compliant with the [CIS Benchmarks](https://learn.cisecurity.org/benchmarks), here you can find a configuration to harden your **kubernetes** installation.
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To apply the hardening configuration, create a file (eg. `hardening.yaml`) and paste the content of the following code snippet into that.
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## Minimum Requirements
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The **kubernetes** version should be at least `v1.23.6` to have all the most recent security features (eg. the new `PodSecurity` admission plugin, etc).
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**N.B.** Some of these configurations have just been added to **kubespray**, so ensure that you have the latest version to make it works properly. Also, ensure that other configurations doesn't override these.
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`hardening.yaml`:
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```yaml
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# Hardening
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---
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## kube-apiserver
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authorization_modes: ['Node', 'RBAC']
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# AppArmor-based OS
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# kube_apiserver_feature_gates: ['AppArmor=true']
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kube_apiserver_request_timeout: 120s
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kube_apiserver_service_account_lookup: true
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# enable kubernetes audit
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kubernetes_audit: true
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audit_log_path: "/var/log/kube-apiserver-log.json"
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audit_log_maxage: 30
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audit_log_maxbackups: 10
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audit_log_maxsize: 100
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tls_min_version: VersionTLS12
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tls_cipher_suites:
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- TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
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- TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
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- TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305
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# enable encryption at rest
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kube_encrypt_secret_data: true
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kube_encryption_resources: [secrets]
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kube_encryption_algorithm: "secretbox"
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kube_apiserver_enable_admission_plugins:
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- EventRateLimit
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- AlwaysPullImages
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- ServiceAccount
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- NamespaceLifecycle
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- NodeRestriction
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- LimitRanger
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- ResourceQuota
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- MutatingAdmissionWebhook
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- ValidatingAdmissionWebhook
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- PodNodeSelector
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- PodSecurity
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kube_apiserver_admission_control_config_file: true
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# EventRateLimit plugin configuration
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kube_apiserver_admission_event_rate_limits:
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limit_1:
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type: Namespace
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qps: 50
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burst: 100
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cache_size: 2000
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limit_2:
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type: User
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qps: 50
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burst: 100
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kube_profiling: false
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## kube-controller-manager
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kube_controller_manager_bind_address: 127.0.0.1
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kube_controller_terminated_pod_gc_threshold: 50
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# AppArmor-based OS
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# kube_controller_feature_gates: ["RotateKubeletServerCertificate=true", "AppArmor=true"]
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kube_controller_feature_gates: ["RotateKubeletServerCertificate=true"]
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## kube-scheduler
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kube_scheduler_bind_address: 127.0.0.1
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kube_kubeadm_scheduler_extra_args:
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profiling: false
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# AppArmor-based OS
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# kube_scheduler_feature_gates: ["AppArmor=true"]
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## etcd
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etcd_deployment_type: kubeadm
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## kubelet
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kubelet_authentication_token_webhook: true
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kube_read_only_port: 0
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kubelet_rotate_server_certificates: true
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kubelet_protect_kernel_defaults: true
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kubelet_event_record_qps: 1
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kubelet_rotate_certificates: true
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kubelet_streaming_connection_idle_timeout: "5m"
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kubelet_make_iptables_util_chains: true
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kubelet_feature_gates: ["RotateKubeletServerCertificate=true", "SeccompDefault=true"]
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kubelet_seccomp_default: true
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kubelet_systemd_hardening: true
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# In case you have multiple interfaces in your
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# control plane nodes and you want to specify the right
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# IP addresses, kubelet_secure_addresses allows you
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# to specify the IP from which the kubelet
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# will receive the packets.
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kubelet_secure_addresses: "192.168.10.110 192.168.10.111 192.168.10.112"
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# additional configurations
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kube_owner: root
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kube_cert_group: root
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# create a default Pod Security Configuration and deny running of insecure pods
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# kube_system namespace is exempted by default
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kube_pod_security_use_default: true
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kube_pod_security_default_enforce: restricted
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```
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Let's take a deep look to the resultant **kubernetes** configuration:
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* The `anonymous-auth` (on `kube-apiserver`) is set to `true` by default. This is fine, because it is considered safe if you enable `RBAC` for the `authorization-mode`.
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* The `enable-admission-plugins` has not the `PodSecurityPolicy` admission plugin. This because it is going to be definitely removed from **kubernetes** `v1.25`. For this reason we decided to set the newest `PodSecurity` (for more details, please take a look here: <https://kubernetes.io/docs/concepts/security/pod-security-admission/>). Then, we set the `EventRateLimit` plugin, providing additional configuration files (that are automatically created under the hood and mounted inside the `kube-apiserver` container) to make it work.
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* The `encryption-provider-config` provide encryption at rest. This means that the `kube-apiserver` encrypt data that is going to be stored before they reach `etcd`. So the data is completely unreadable from `etcd` (in case an attacker is able to exploit this).
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* The `rotateCertificates` in `KubeletConfiguration` is set to `true` along with `serverTLSBootstrap`. This could be used in alternative to `tlsCertFile` and `tlsPrivateKeyFile` parameters. Additionally it automatically generates certificates by itself, but you need to manually approve them or at least using an operator to do this (for more details, please take a look here: <https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/>).
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* If you are installing **kubernetes** in an AppArmor-based OS (eg. Debian/Ubuntu) you can enable the `AppArmor` feature gate uncommenting the lines with the comment `# AppArmor-based OS` on top.
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* The `kubelet_systemd_hardening`, both with `kubelet_secure_addresses` setup a minimal firewall on the system. To better understand how these variables work, here's an explanatory image:
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Once you have the file properly filled, you can run the **Ansible** command to start the installation:
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```bash
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ansible-playbook -v cluster.yml \
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-i inventory.ini \
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-b --become-user=root \
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--private-key ~/.ssh/id_ecdsa \
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-e "@vars.yaml" \
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-e "@hardening.yaml"
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```
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**N.B.** The `vars.yaml` contains our general cluster information (SANs, load balancer, dns, etc..) and `hardening.yaml` is the file described above.
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Once completed the cluster deployment, don't forget to approve the generated certificates (check them with `kubectl get csr`, approve with `kubectl certificate approve <csr_name>`). This action is necessary because the `secureTLSBootstrap` option and `RotateKubeletServerCertificate` feature gate for `kubelet` are enabled (CIS [4.2.11](https://www.tenable.com/audits/items/CIS_Kubernetes_v1.20_v1.0.0_Level_1_Worker.audit:05af3dfbca8e0c3fb3559c6c7de29191), [4.2.12](https://www.tenable.com/audits/items/CIS_Kubernetes_v1.20_v1.0.0_Level_1_Worker.audit:5351c76f8c5bff8f98c29a5200a35435)).
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