Add conditionals for IPv6 sysctl settings

This way the playbooks won't try to set ipv6 systemctl options
unless ipv6 is available on the system.

Closes-bug: #1906306
Change-Id: Icccfc1c509179c3cfd59650b7917a637f9af9646

ansible/roles/loadbalancer/tasks/config-host.yml

@@ -1,4 +1,10 @@
 ---
+
+- name: Check IPv6 support
+  command: /usr/sbin/sysctl -n net.ipv6.conf.all.disable_ipv6
+  register: ipv6_disabled
+  changed_when: false
+
 - name: Setting sysctl values
   vars:
     should_set: "{{ item.value != 'KOLLA_UNSET' }}"
@@ -17,6 +23,7 @@
   when:
     - set_sysctl | bool
     - item.value != 'KOLLA_SKIP'
+    - not ('ipv6' in item.name and ipv6_disabled.stdout | bool)
 
 - name: Load and persist keepalived module
   import_role:

ansible/roles/neutron/tasks/config-host.yml

@@ -12,6 +12,11 @@
     list |
     length > 0
 
+- name: Check IPv6 support
+  command: /usr/sbin/sysctl -n net.ipv6.conf.all.disable_ipv6
+  register: ipv6_disabled
+  changed_when: false
+
 - name: Setting sysctl values
   become: true
   vars:
@@ -34,3 +39,4 @@
     - set_sysctl | bool
     - item.value != 'KOLLA_SKIP'
     - (neutron_l3_agent.enabled | bool and neutron_l3_agent.host_in_groups | bool)
+    - not ('ipv6' in item.name and ipv6_disabled.stdout | bool)

releasenotes/notes/bug-1906306-640d5085576656f9.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Add conditionals for IPv6 sysctl settings
+    that have IPV6 disabled in kernel.
+    Changing sysctl settings related to IPv6 on those
+    systems lead to errors.
+    `LP#1906306 <https://launchpad.net/bugs/1906306>`__