Enhance entrypoint and deployment configurations for Kubernetes management pod

- Add K8S_RUNTIME_ENV_PROFILE and KUBERNETES_SECRETS_DIR variables in entrypoint.sh
- Implement service account kubeconfig installation and environment variable persistence
- Update deployment.yaml to include fsGroup and fsGroupChangePolicy in securityContext
- Modify container ports and resource limits for better management

entrypoint.sh

@@ -4,12 +4,14 @@ set -Eeuo pipefail
 STATE_DIR="/var/lib/k8s-mgmt-pod"
 GENERATED_PASSWORDS_FILE="${STATE_DIR}/generated-passwords.env"
 SSH_DYNAMIC_CONFIG="/etc/ssh/sshd_config.d/20-k8s-mgmt-pod-auth.conf"
+K8S_RUNTIME_ENV_PROFILE="/etc/profile.d/30-kubernetes-runtime-env.sh"
 PASSWORD_AUTH_REQUIRED=0
 SSHD_PID=""
 WEBSSH2_PID=""
 NGINX_PID=""
 BOOTSTRAP_KUBECONFIG="${BOOTSTRAP_KUBECONFIG:-/bootstrap/kubeconfig/config}"
 ENABLE_BOOTSTRAP_KUBECONFIG="${ENABLE_BOOTSTRAP_KUBECONFIG:-false}"
+KUBERNETES_SECRETS_DIR="${KUBERNETES_SECRETS_DIR:-/var/run/kubernetes.io}"
 SSH_PORT="${SSH_PORT:-2222}"
 
 if [[ -z "${WEBSSH2_SSH_PORT:-}" ]]; then
@@ -96,12 +98,84 @@ write_authorized_keys() {
 
 install_kubeconfig_for_user() {
   local username="$1"
+  local source_kubeconfig="$2"
   local home_dir="/home/${username}"
   local kube_dir="${home_dir}/.kube"
   local kube_config="${kube_dir}/config"
 
   mkdir -p "${kube_dir}"
-  install -m 0600 -o "${username}" -g "${username}" "${BOOTSTRAP_KUBECONFIG}" "${kube_config}"
+  install -m 0600 -o "${username}" -g "${username}" "${source_kubeconfig}" "${kube_config}"
+}
+
+resolve_kubernetes_secrets_dir() {
+  local configured_dir="${KUBERNETES_SECRETS_DIR}"
+  local fallback_dir="/var/run/secrets/kubernetes.io/serviceaccount"
+
+  if [[ -f "${configured_dir}/token" && -f "${configured_dir}/ca.crt" && -f "${configured_dir}/namespace" ]]; then
+    printf '%s\n' "${configured_dir}"
+    return 0
+  fi
+
+  if [[ "${configured_dir}" != "${fallback_dir}" ]] \
+    && [[ -f "${fallback_dir}/token" && -f "${fallback_dir}/ca.crt" && -f "${fallback_dir}/namespace" ]]; then
+    printf '%s\n' "${fallback_dir}"
+    return 0
+  fi
+
+  return 1
+}
+
+install_serviceaccount_kubeconfig() {
+  local sa_dir=""
+  local token_file=""
+  local ca_file=""
+  local namespace_file=""
+  local namespace=""
+  local kubernetes_host="${KUBERNETES_SERVICE_HOST:-kubernetes.default.svc}"
+  local kubernetes_port="${KUBERNETES_SERVICE_PORT_HTTPS:-443}"
+  local server=""
+  local generated_kubeconfig="${STATE_DIR}/incluster.kubeconfig"
+
+  if ! sa_dir="$(resolve_kubernetes_secrets_dir)"; then
+    log "Skipping in-cluster kubeconfig generation because no service-account mount was found in ${KUBERNETES_SECRETS_DIR} or /var/run/secrets/kubernetes.io/serviceaccount."
+    return
+  fi
+
+  token_file="${sa_dir}/token"
+  ca_file="${sa_dir}/ca.crt"
+  namespace_file="${sa_dir}/namespace"
+  namespace="$(tr -d '\n' < "${namespace_file}")"
+  if [[ -z "${namespace}" ]]; then
+    namespace="default"
+  fi
+
+  server="https://${kubernetes_host}:${kubernetes_port}"
+
+  cat > "${generated_kubeconfig}" <<EOF
+apiVersion: v1
+kind: Config
+clusters:
+- name: in-cluster
+  cluster:
+    certificate-authority: ${ca_file}
+    server: ${server}
+contexts:
+- name: in-cluster
+  context:
+    cluster: in-cluster
+    user: service-account
+    namespace: ${namespace}
+current-context: in-cluster
+users:
+- name: service-account
+  user:
+    tokenFile: ${token_file}
+EOF
+
+  chmod 0600 "${generated_kubeconfig}"
+  install_kubeconfig_for_user admin "${generated_kubeconfig}"
+  install_kubeconfig_for_user user "${generated_kubeconfig}"
+  log "Installed generated in-cluster kubeconfig for admin and user from ${sa_dir}."
 }
 
 install_bootstrap_kubeconfig() {
@@ -114,8 +188,8 @@ install_bootstrap_kubeconfig() {
     return
   fi
 
-  install_kubeconfig_for_user admin
-  install_kubeconfig_for_user user
+  install_kubeconfig_for_user admin "${BOOTSTRAP_KUBECONFIG}"
+  install_kubeconfig_for_user user "${BOOTSTRAP_KUBECONFIG}"
   log "Installed mounted kubeconfig for admin and user."
 }
 
@@ -199,10 +273,27 @@ KbdInteractiveAuthentication ${keyboard_interactive_value}
 EOF
 }
 
+persist_kubernetes_login_env() {
+  local kubernetes_host="${KUBERNETES_SERVICE_HOST:-kubernetes.default.svc}"
+  local kubernetes_https_port="${KUBERNETES_SERVICE_PORT_HTTPS:-443}"
+  local kubernetes_port="${KUBERNETES_SERVICE_PORT:-${kubernetes_https_port}}"
+
+  cat > "${K8S_RUNTIME_ENV_PROFILE}" <<EOF
+# Generated at container start so SSH login shells see Kubernetes API environment values.
+export KUBERNETES_SERVICE_HOST='${kubernetes_host}'
+export KUBERNETES_SERVICE_PORT='${kubernetes_port}'
+export KUBERNETES_SERVICE_PORT_HTTPS='${kubernetes_https_port}'
+EOF
+
+  chmod 0644 "${K8S_RUNTIME_ENV_PROFILE}"
+}
+
 prepare_runtime() {
   mkdir -p /var/run/sshd
   ensure_host_keys
+  install_serviceaccount_kubeconfig
   install_bootstrap_kubeconfig
+  persist_kubernetes_login_env
   configure_user_auth admin ADMIN_SSH_PUBKEY ADMIN_PASSWORD
   configure_user_auth user USER_SSH_PUBKEY USER_PASSWORD
   render_sshd_auth_config

k8s/deployment.yaml

@@ -16,20 +16,24 @@ spec:
     spec:
       serviceAccountName: k8s-mgmt-pod
       automountServiceAccountToken: true
+
       securityContext:
         seccompProfile:
           type: RuntimeDefault
+        fsGroup: 1000
+        fsGroupChangePolicy: OnRootMismatch
+
       containers:
         - name: k8s-mgmt-pod
           image: git.alcatrash.net/michael/k8s-mgmt-pod/k8s-mgmt-pod:latest
           imagePullPolicy: Always
+
           ports:
             - name: ssh
               containerPort: 2222
-              protocol: TCP
             - name: webssh
               containerPort: 3000
-              protocol: TCP
+
           env:
             - name: ADMIN_SSH_PUBKEY
               valueFrom:
@@ -55,6 +59,7 @@ spec:
                   name: k8s-mgmt-pod-auth
                   key: USER_PASSWORD
                   optional: true
+
           resources:
             requests:
               cpu: 100m
@@ -62,30 +67,41 @@ spec:
             limits:
               cpu: 500m
               memory: 512Mi
+
           readinessProbe:
             tcpSocket:
               port: 2222
             initialDelaySeconds: 5
             periodSeconds: 10
+
           livenessProbe:
             tcpSocket:
               port: 2222
             initialDelaySeconds: 15
             periodSeconds: 20
+
           volumeMounts:
             - name: state
               mountPath: /var/lib/k8s-mgmt-pod
+
           securityContext:
-            # sshd still runs as root to switch to authenticated user sessions.
-            # Binding uses a non-privileged port, so NET_BIND_SERVICE is not required.
             runAsUser: 0
             runAsGroup: 0
             runAsNonRoot: false
             allowPrivilegeEscalation: false
             readOnlyRootFilesystem: false
             capabilities:
-              drop: ["ALL"]
-              add: ["CHOWN", "DAC_OVERRIDE", "FOWNER", "SETGID", "SETUID", "SYS_CHROOT"]
+              drop:
+                - ALL
+              add:
+                - AUDIT_WRITE
+                - CHOWN
+                - DAC_OVERRIDE
+                - FOWNER
+                - SETGID
+                - SETUID
+                - SYS_CHROOT
+
       volumes:
         - name: state
           emptyDir: {}