Add sshd dns toggle to speed up Ansible

This adds a setting (disabled by default) to have the browbeat
installation playbook add the value

UseDNS no

to the overcloud node sshd config, for the scale lab exspecially this
can result in a 4x or greater speed improvement running ansible playbooks.

Not quite ludicrous speed, that's going to require pipelining, but it will do

Change-Id: I660cfc5a815bd08337f71e2ed9f97252794b09e2

ansible/install/browbeat.yml

@@ -6,6 +6,7 @@
 - hosts: controller
   remote_user: "{{ host_remote_user }}"
   roles:
+    - no-sshd-dns
     - shaker-check
 
 - hosts: undercloud
@@ -13,3 +14,8 @@
   roles:
     - common
     - browbeat
+
+- hosts: compute
+  remote_user: "{{ host_remote_user }}"
+  roles:
+    - no-sshd-dns

ansible/install/group_vars/all.yml

@@ -51,6 +51,9 @@ images:
 # DNS Server to add
 dns_server: 8.8.8.8
 
+# Disables dns lookup by overcloud sshd process
+disable_ssh_dns: false
+
 # epel7 rpm for collectd packages
 epel7_rpm: https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
 

ansible/install/roles/no-sshd-dns/tasks/main.yml

@@ -0,0 +1,12 @@
+# Disables DNS lookup in the overcloud sshd config file. Speeds up operations in environments with slow dns servers hugely.
+---
+
+- name: Disable DNS resolution in Overcloud sshd config
+  lineinfile: dest=/etc/ssh/sshd_config line="UseDNS no" state=present
+  become: true
+  when: "{{disable_ssh_dns}}"
+
+- name: Restart sshd service
+  service: name=sshd state=restarted
+  become: true
+  when: "{{disable_ssh_dns}}"