docs: add hardening guide (#8868)

README.md

@@ -111,6 +111,7 @@ vagrant up
 - [Adding/replacing a node](docs/nodes.md)
 - [Upgrades basics](docs/upgrades.md)
 - [Air-Gap installation](docs/offline-environment.md)
+- [Hardening](docs/hardening.md)
 - [Roadmap](docs/roadmap.md)
 
 ## Supported Linux Distributions

docs/hardening.md

@@ -0,0 +1,110 @@
+# Cluster Hardening
+
+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.
+
+To apply the hardening configuration, create a file (eg. `hardening.yaml`) and paste the content of the following code snippet into that.
+
+## Minimum Requirements
+
+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).
+
+**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.
+
+`hardening.yaml`:
+
+```yaml
+# Hardening
+---
+
+## kube-apiserver
+authorization_modes: ['Node','RBAC']
+# AppArmor-based OS
+#kube_apiserver_feature_gates: ['AppArmor=true']
+kube_apiserver_request_timeout: 120s
+kube_apiserver_service_account_lookup: true
+
+# enable kubernetes audit
+kubernetes_audit: true
+audit_log_path: "/var/log/kube-apiserver-log.json"
+audit_log_maxage: 30
+audit_log_maxbackups: 10
+audit_log_maxsize: 100
+
+tls_min_version: VersionTLS12
+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
+
+# enable encryption at rest
+kube_encrypt_secret_data: true
+kube_encryption_resources: [secrets]
+kube_encryption_algorithm: "secretbox"
+
+kube_apiserver_enable_admission_plugins: ['EventRateLimit,AlwaysPullImages,ServiceAccount,NamespaceLifecycle,NodeRestriction,LimitRanger,ResourceQuota,MutatingAdmissionWebhook,ValidatingAdmissionWebhook,PodNodeSelector,PodSecurity']
+kube_apiserver_admission_control_config_file: true
+# EventRateLimit plugin configuration
+kube_apiserver_admission_event_rate_limits:
+  limit_1:
+    type: Namespace
+    qps: 50
+    burst: 100
+    cache_size: 2000
+  limit_2:
+    type: User
+    qps: 50
+    burst: 100
+kube_profiling: false
+
+## kube-controller-manager
+kube_controller_manager_bind_address: 127.0.0.1
+kube_controller_terminated_pod_gc_threshold: 50
+# AppArmor-based OS
+#kube_controller_feature_gates: ["RotateKubeletServerCertificate=true","AppArmor=true"]
+kube_controller_feature_gates: ["RotateKubeletServerCertificate=true"]
+
+## kube-scheduler
+kube_scheduler_bind_address: 127.0.0.1
+kube_kubeadm_scheduler_extra_args:
+  profiling: false
+# AppArmor-based OS
+#kube_scheduler_feature_gates: ["AppArmor=true"]
+
+## etcd
+etcd_deployment_type: kubeadm
+
+## kubelet
+kubelet_authorization_mode_webhook: true
+kubelet_authentication_token_webhook: true
+kube_read_only_port: 0
+kubelet_rotate_server_certificates: true
+kubelet_protect_kernel_defaults: true
+kubelet_event_record_qps: 1
+kubelet_rotate_certificates: true
+kubelet_streaming_connection_idle_timeout: "5m"
+kubelet_make_iptables_util_chains: true
+kubelet_feature_gates: ["RotateKubeletServerCertificate=true"]
+```
+
+Let's take a deep look to the resultant **kubernetes** configuration:
+
+* 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`.
+* 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.
+* 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).
+* 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/>).
+* 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.
+
+Once you have the file properly filled, you can run the **Ansible** command to start the installation:
+
+```bash
+ansible-playbook -v cluster.yml \
+        -i inventory.ini \
+        -b --become-user=root \
+        --private-key ~/.ssh/id_ecdsa \
+        -e "@vars.yaml" \
+        -e "@hardening.yaml"
+```
+
+**N.B.** The `vars.yaml` contains our general cluster information (SANs, load balancer, dns, etc..) and `hardening.yaml` is the file described above.
+
+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)).