Add a --display argument to kayobe physical network configure

This will output the candidate configuration, without applying it.

ansible/physical-network.yml

@@ -16,6 +16,9 @@
     # to configure in order to restrict configuration to a subset of
     # interfaces.
     physical_network_interface_description_limit: ''
+    # Set this variable to True in order to display the candidate switch
+    # configuration and exit without applying it.
+    physical_network_display: False
   tasks:
     - name: Fail if both interface name and description limits are specified
       fail:
@@ -30,6 +33,10 @@
       group_by:
         key: "switches_of_type_{{ switch_type }}"
 
+    - name: Group hosts by whether display mode is set
+      group_by:
+        key: "switches_in_display_mode_{{ physical_network_display | bool }}"
+
     - name: Add discovery interface configuration when performing discovery
       set_fact:
         switch_interface_config: >
@@ -50,8 +57,20 @@
              switch_interface_config_select_description(physical_network_interface_description_limit.split(",")) }}
       when: physical_network_interface_description_limit != ''
 
+- name: Display switch configuration
+  hosts: switches_in_display_mode_True
+  gather_facts: no
+  tasks:
+    - name: Display the candidate global switch configuration
+      debug:
+        var: switch_config
+
+    - name: Display the candidate switch interface configuration
+      debug:
+        var: switch_interface_config
+
 - name: Ensure DellOS physical switches are configured
-  hosts: switches_of_type_dellos6:switches_of_type_dellos9
+  hosts: switches_of_type_dellos6:switches_of_type_dellos9:&switches_in_display_mode_False
   gather_facts: no
   roles:
     - role: ssh-known-host
@@ -63,7 +82,7 @@
       dell_switch_interface_config: "{{ switch_interface_config }}"
 
 - name: Ensure Juniper physical switches are configured
-  hosts: switches_of_type_junos
+  hosts: switches_of_type_junos:&switches_in_display_mode_False
   gather_facts: no
   roles:
     - role: ssh-known-host

doc/source/deployment.rst

@@ -50,6 +50,9 @@ The names or descriptions should be separated by commas.  This may be useful
 when adding compute nodes to an existing deployment, in order to avoid changing
 the configuration interfaces in use by active nodes.
 
+The ``display`` argument will display the candidate switch configuration,
+without actually applying it.
+
 Seed Hypervisor
 ===============
 

doc/source/release-notes.rst

@@ -11,6 +11,8 @@ Features
 * Adds ``--interface-limit`` and ``--interface-description-limit`` arguments to
   the ``kayobe physical network configure`` command.  These arguments allow
   configuration to be limited to a subset of switch interfaces.
+* Adds a ``display`` argument to ``kayobe physical network configure`` command.
+  This will output the candidate switch configuration without applying it.
 
 Upgrade Notes
 -------------

kayobe/cli/commands.py

@@ -227,6 +227,9 @@ class PhysicalNetworkConfigure(KayobeAnsibleMixin, VaultMixin, Command):
         group = parser.add_argument_group("Physical Networking")
         group.add_argument("--group", required=True,
                            help="the Ansible group to apply configuration to")
+        group.add_argument("--display", action="store_true",
+                           help="display the candidate configuration and exit "
+                                "without applying it")
         group.add_argument("--enable-discovery", action="store_true",
                            help="configure the network for hardware discovery")
         group.add_argument("--interface-limit",
@@ -240,6 +243,7 @@ class PhysicalNetworkConfigure(KayobeAnsibleMixin, VaultMixin, Command):
     def take_action(self, parsed_args):
         self.app.LOG.debug("Configuring a physical network")
         extra_vars = {}
+        extra_vars["physical_network_display"] = parsed_args.display
         if parsed_args.enable_discovery:
             extra_vars["physical_network_enable_discovery"] = True
         if parsed_args.interface_limit: