Support skipping SSH keyscan for older switch devices

Some network devices may use SSH key exchange algorithms that are no
longer supported by the Ansible control host. This will cause
ssh-keyscan to fail, preventing Kayobe from configuring the devices.
This change makes it possible to work around the issue by setting
switch_skip_keyscan to true for the affected devices. The SSH known
hosts file on the Ansible control host will need to be populated
manually.

Change-Id: I4e3394cff1fd86eb5c1a4be55d6fd7fd080b2944

ansible/inventory/group_vars/all/switches/keyscan

+---
+# Whether to skip scanning SSH keys for switches. In some cases scanning SSH
+# keys may fail e.g. due to unsupported key exchange algorithms on older
+# devices.  Default is false.
+switch_skip_keyscan: false

ansible/physical-network.yml

@@ -117,6 +117,7 @@
        default(100) }}
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: arista-switch
       arista_switch_type: "{{ switch_type }}"
@@ -133,6 +134,7 @@
        default(100) }}
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: dell-switch
       dell_switch_type: "{{ switch_type }}"
@@ -150,6 +152,7 @@
        default(100) }}
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: stackhpc.network.dell_powerconnect_switch
       dell_powerconnect_switch_type: "{{ switch_type }}"
@@ -166,6 +169,7 @@
        default(100) }}
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: junos-switch
       junos_switch_type: "{{ switch_type }}"
@@ -183,6 +187,7 @@
        default(100) }}
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: stackhpc.network.mellanox_switch
       mellanox_switch_type: "{{ switch_type }}"
@@ -199,6 +204,7 @@
        default(100) }}
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: nclu-switch
       nclu_switch_config: "{{ switch_config }}"
@@ -209,6 +215,7 @@
   gather_facts: no
   roles:
     - role: ssh-known-host
+      when: not switch_skip_keyscan | bool
 
     - role: nvue-switch
       nvue_switch_config: "{{ switch_config }}"

doc/source/configuration/reference/physical-network.rst

@@ -181,6 +181,15 @@ example:
        description: compute0
        config: "{{ switch_interface_config_compute }}"
 
+Support for Older Devices
+=========================
+
+Some network devices may use SSH key exchange algorithms that are no longer
+supported by the Ansible control host. This will cause ``ssh-keyscan`` to fail,
+preventing Kayobe from configuring the devices. To work around this, set
+``switch_skip_keyscan`` to ``true`` for the affected devices. The SSH known
+hosts file on the Ansible control host will need to be populated manually.
+
 .. _physical-network-device-specific:
 
 Device-specific Configuration Variables

releasenotes/notes/switch-skip-keyscan-23b1f5006f443323.yaml

+---
+features:
+  - |
+    Adds support for skipping SSH keyscan when configuring switches using
+    ``kayobe physical network configure`` using a ``switch_skip_keyscan``
+    variable.