Beginning work on instance registration, sanity checks.

awx/main/management/commands/register_instance.py

@@ -0,0 +1,71 @@
+# Copyright (c) 2014 Ansible, Inc.
+# All Rights Reserved
+
+from optparse import make_option
+
+from django.conf import settings
+from django.core.management.base import BaseCommand, CommandError
+
+from awx.main.models import Instance
+
+
+class Command(BaseCommand):
+    """Regsiter this instance with the database for HA tracking.
+
+    This command is idempotent. It will register the machine if it is not
+    yet present and do nothing if the machine is already registered.
+
+    If a second primary machine is registered, the first primary machine will
+    become a secondary machine, and the newly registered primary machine
+    will be primary (unless `--timid` is provided, in which case the command
+    will simply error out).
+
+    This command will also error out under the following circumstances:
+
+      * Attempting to register a secondary machine with no primary machines.
+      * Attempting to register this machine with a different state than its
+        existing registration plus `--timid`.
+    """
+    option_list = BaseCommand.option_list + (
+        make_option('--timid', action='store_true', dest='timid'),
+        make_option('--primary', action='store_true', dest='primary'),
+        make_option('--secondary', action='store_false', dest='primary'),
+    )
+
+    def handle(self, **options):
+        uuid = settings.SYSTEM_UUID
+
+        # Is there an existing record for this machine?
+        # If so, retrieve that record and look for issues.
+        try:
+            instance = Instance.objects.get(uuid=uuid)
+            existing = True
+        except Instance.DoesNotExist:
+            instance = Instance(uuid=uuid)
+            existing = False
+
+        # Get a status on primary machines (excluding this one, regardless
+        # of its status).
+        other_instances = Instance.objects.exclude(uuid=uuid)
+        primaries = other_instances.filter(primary=True).count()
+
+        # Sanity check: If we're supposed to be being timid, then ensure
+        # that there's no crazy mosh pits happening here.
+        #
+        # If the primacy setting doesn't match what is already on
+        # the instance, error out.
+        if existing and timid and instance.primary != options['primary']:
+            raise CommandError('This instance is already registered as a '
+                               '%s instance.' % instance.role)
+
+        # If this instance is being set to primary and a *different* primary
+        # machine already exists, then error out if we're supposed to be timid.
+        if timid and instance.primary and primaries:
+            raise CommandError('Another instance is already registered as '
+                               'primary.')
+
+        # Lastly, if there are no primary machines at all, then don't allow
+        # this to be registered as a secondary machine.
+        if not instance.primary and not primaries:
+            raise CommandError('Unable to register a secondary machine until '
+                               'a primary machine has been registered')