Add basis for VM scheduling to hypervisors

.gitignore

@@ -2,6 +2,8 @@
 .*
 # Ansible retry files
 *.retry
+# Tenks allocations file
+allocations.yml
 
 # Byte-compiled / optimized / DLL files
 __pycache__/

ansible/action_plugins/tenks_schedule.py

@@ -0,0 +1,69 @@
+# Avoid shadowing of system copy module by copy action plugin.
+from __future__ import absolute_import
+from copy import deepcopy
+import operator
+
+from ansible.errors import AnsibleActionFail
+from ansible.module_utils._text import to_text
+from ansible.plugins.action import ActionBase
+from six import iteritems
+
+
+class ActionModule(ActionBase):
+
+    def run(self, tmp=None, task_vars=None):
+        """
+        Schedule specifications of VMs by flavour onto hypervisors.
+
+        :param hypervisor_vars: A dict of hostvars for each hypervisor, keyed
+                                by hypervisor hostname.
+        :param specs: A dict mapping flavour names to the number of VMs
+                      required of that flavour.
+        :param flavours: A dict mapping flavour names to a dict of properties
+                         of that flavour.
+        :param vm_name_prefix: A string with with to prefix all sequential VM
+                               names.
+        :returns: A dict containing lists of VM details, keyed by the
+                  hostname of the hypervisor to which they are scheduled.
+        :raises: AnsibleError if insufficient hypervisors exist to host the
+                 requested VMs.
+        """
+        result = super(ActionModule, self).run(tmp, task_vars)
+        del tmp  # tmp no longer has any effect
+        self._validate_vars(task_vars)
+
+        vms = []
+        idx = 0
+        for flav, cnt in iteritems(task_vars['specs']):
+            for _ in xrange(cnt):
+                vm = deepcopy(task_vars['flavours'][flav])
+                # Sequentially number the VM names.
+                vm['name'] = "%s%d" % (task_vars['vm_name_prefix'], idx)
+                vms.append(vm)
+                idx += 1
+
+        # TODO(w-miller): currently we just arbitrarily schedule all VMs to the
+        # first hypervisor. Improve this algorithm to make it more
+        # sophisticated.
+        result['result'] = {task_vars['hypervisor_vars'].keys()[0]: vms}
+        return result
+
+    def _validate_vars(self, task_vars):
+        if task_vars is None:
+            task_vars = {}
+
+        REQUIRED_TASK_VARS = {'hypervisor_vars', 'specs', 'flavours'}
+        OPTIONAL_TASK_VARS = {('vm_name_prefix', 'vm')}
+        for var in REQUIRED_TASK_VARS:
+            if var not in task_vars:
+                e = "The parameter '%s' must be specified." % var
+                raise AnsibleActionFail(to_text(e))
+
+        for var in OPTIONAL_TASK_VARS:
+            if var[0] not in task_vars:
+                task_vars[var[0]] = var[1]
+
+        if not task_vars['hypervisor_vars']:
+            e = ("There are no hosts in the 'hypervisors' group to which we "
+                 "can schedule.")
+            raise AnsibleActionFail(to_text(e))

ansible/schedule.yml

@@ -0,0 +1,29 @@
+---
+# Ensure we have facts about all hypervisors before scheduling begins.
+- name: Gather facts from hypervisors
+  setup:
+  delegate_to: "{{ item }}"
+  delegate_facts: true
+  loop: "{{ groups['hypervisors'] }}"
+
+# Creates a dict mapping each hypervisor's hostname to its hostvars, to be used
+# during scheduling.
+- name: Collect hypervisor hostvars
+  set_fact:
+    hypervisor_vars: >
+      {{ hypervisor_vars | default({}) | combine({item: hostvars[item]}) }}
+  with_items: "{{ groups['controllers'] }}"
+
+- name: Schedule VMs to hypervisors
+  tenks_schedule:
+    hypervisor_vars: "{{ hypervisor_vars }}"
+    flavours: "{{ flavours }}"
+    specs: "{{ specs }}"
+  register: allocations
+
+- name: Write VM allocations to file
+  copy:
+    # tenks_schedule lookup plugin outputs a dict. Pretty-print this to persist
+    # it in a YAML file.
+    content: "{{ allocations.result | to_nice_yaml }}"
+    dest: "{{ base_path }}/allocations.yml"