ansible: omit nonexistant hosts from inventory groups

Otherwise, we would get spurious "UNREACHABLE" errors during
provisioning. This could be due wither to mistakes in the lxdock config
file or to a command line filtering of the hosts.

lxdock/provisioners/ansible.py

@@ -42,10 +42,12 @@ def line(guest):
             return '{} ansible_host={} ansible_user=root'.format(guest.container.name, ip)
 
         def fmtgroup(name, hosts):
+            hosts = [host for host in hosts if host in guestnames]
             return '[{}]\n{}'.format(name, '\n'.join(hosts))
 
         all_hosts_lines = '\n'.join(line(guest) for guest in self.guests)
         groups = self.options.get('groups', {})
+        guestnames = {guest.container.name for guest in self.guests}
         groups_lines = '\n\n'.join(fmtgroup(key, val) for key, val in groups.items())
         return '\n\n'.join([all_hosts_lines, groups_lines])
 

tests/unit/provisioners/test_ansible.py

@@ -56,11 +56,15 @@ def test_can_properly_setup_ssh_for_alpine_guests(self):
     def test_inventory_contains_groups(self):
         c1 = FakeContainer(name='c1')
         c2 = FakeContainer(name='c2')
+        # c3 is deliberately not part of our guests list. This is to test that it doesn't end up
+        # in the inventory and result in spurious unreachable hosts. These situations can happen
+        # in two ways: errors in the config file, or guest filtering in the command line ("lxdock
+        # provision c1, c2" for example).
         provisioner = AnsibleProvisioner(
             './',
             Host(),
             [DebianGuest(c1), DebianGuest(c2)],
-            {'playbook': 'deploy.yml', 'groups': {'g1': ['c1', 'c2'], 'g2': ['c1']}}
+            {'playbook': 'deploy.yml', 'groups': {'g1': ['c1', 'c2'], 'g2': ['c1', 'c3']}}
         )
         inv = provisioner.get_inventory()
         # group order is not guaranteed. our tests have to be written with that in mind.