Check if changes have made before attempting a rebalance

Utilize the "ringbuilder.devs_changed" option to ensure that the ring
needs a rebalance. This will prevent unnecessary rebalances that cause
failures due to "min_part_hours" not being passed even though no changes
were required.

Additionally, we can now return a correct Ansible repsonse when the ring
has changed/rebalanced - and return "OK" when it hasn't returned at all.

Change-Id: I1fb4b3544a50ab5f566b3846d616107a84ff29c9

tasks/swift_rings_build.yml

@@ -48,9 +48,11 @@
   with_nested:
     - [ 'account', 'container' ]
     - "{{ swift_managed_regions | default([None]) }}"
+  register: swift_rings_create
   become: yes
   become_user: "{{ swift_system_user_name }}"
-  changed_when: false
+  changed_when: "{{ swift_rings_create.rc not in [1, 2, 3] }}"
+  failed_when: "{{ swift_rings_create.rc in [1, 2] }}"
   args:
     chdir: /etc/swift/ring_build_files/
 
@@ -59,8 +61,10 @@
   with_nested:
     - "{{ swift.storage_policies }}"
     - "{{ swift_managed_regions | default([None]) }}"
+  register: swift_object_rings_create
   become: yes
   become_user: "{{ swift_system_user_name }}"
-  changed_when: false
+  changed_when: "{{ swift_object_rings_create.rc not in [1, 2, 3] }}"
+  failed_when: "{{ swift_object_rings_create.rc in [1, 2] }}"
   args:
     chdir: /etc/swift/ring_build_files/

templates/swift_rings.py.j2

@@ -140,11 +140,12 @@ def build_ring(build_name, repl, min_part_hours, part_power, hosts,
 
     # Rebalance ring
     if not validate:
-        if not hosts:
+        if not hosts or not ringbuilder.devs_changed:
             ringdata = ringbuilder.get_ring()
             ringdata.save(join(backup_folder, '%d.' % ts +
                                basename(ring_file)))
             ringdata.save(ring_file)
+            exit(3)
         else:
             if reset_mph_clock:
                 ringbuilder.pretend_min_part_hours_passed()

tests/os_swift-overrides.yml

@@ -21,6 +21,8 @@ bridges:
   - name: "br-repl"
     ip_addr: "10.1.3.1"
 
+swift_pretend_min_part_hours_passed: False
+
 swift:
   storage_network: "{{ test_swift_storage_network | default('eth2') }}"
   replication_network: "{{ test_swift_repl_network | default('eth3') }}"