fix: lower node mtu for registry egress

ansible/roles/common/defaults/main.yml

@@ -1,5 +1,6 @@
 ---
 common_upgrade_packages: false
+common_node_mtu: 1400
 tailscale_auth_key: ""
 tailscale_ssh: false
 tailscale_accept_routes: false

ansible/roles/common/tasks/main.yml

@@ -17,6 +17,31 @@
     )
   when: cloud_init_binary.rc == 0
 
+- name: Persist primary interface MTU for registry egress
+  copy:
+    dest: /etc/netplan/99-k8s-mtu.yaml
+    content: |
+      network:
+        version: 2
+        ethernets:
+          {{ ansible_default_ipv4.interface | default('eth0') }}:
+            mtu: {{ common_node_mtu }}
+    mode: "0600"
+  register: k8s_mtu_netplan
+  when: common_node_mtu | int > 0
+
+- name: Apply primary interface MTU immediately
+  command: ip link set dev {{ ansible_default_ipv4.interface | default('eth0') }} mtu {{ common_node_mtu }}
+  changed_when: false
+  when: common_node_mtu | int > 0
+
+- name: Apply persisted MTU netplan
+  command: netplan apply
+  changed_when: true
+  when:
+    - common_node_mtu | int > 0
+    - k8s_mtu_netplan.changed
+
 - name: Update apt cache
   apt:
     update_cache: true