Add Instance HA docs

IHA docs around the instance-ha blueprint

Change-Id: I241704c1821e91c8c7fd006e2dafee8609c186c2

doc/source/install/advanced_deployment/features.rst

@@ -15,6 +15,7 @@ Documentation on how to enable and configure various features available in
    node_placement
    ops_tools
    high_availability
+   instance_ha
    baremetal_overcloud
    ovs_dpdk_config
    deployed_server

doc/source/install/advanced_deployment/instance_ha.rst

@@ -0,0 +1,71 @@
+Configuring Instance High Availability
+======================================
+
+|project|, starting with the Queens release, supports a form of instance
+high availability when the overcloud is deployed in a specific way.
+
+In order to activate instance high-availability (also called ``IHA``)
+the following steps are needed:
+
+1. Add the following environment file to your overcloud deployment command. Make sure you are deploying an HA overcloud::
+
+   -e /usr/share/openstack-tripleo-heat-templates/environments/compute-instanceha.yaml
+
+2. Instead of using the ``Compute`` role use the ``ComputeInstanceHA`` role for your compute plane. The ``ComputeInstanceHA`` role has the following additional services when compared to the ``Compute`` role::
+
+   - OS::TripleO::Services::ComputeInstanceHA
+   - OS::TripleO::Services::PacemakerRemote
+
+3. Make sure that fencing is configured for the whole overcloud (controllers and computes). You can do so by adding an environment file to your deployment command that contains the necessary fencing information. For example::
+
+    parameter_defaults:
+      EnableFencing: true
+      FencingConfig:
+        devices:
+        - agent: fence_ipmilan
+          host_mac: 00:ec:ad:cb:3c:c7
+          params:
+            login: admin
+            ipaddr: 192.168.24.1
+            ipport: 6230
+            passwd: password
+            lanplus: 1
+        - agent: fence_ipmilan
+          host_mac: 00:ec:ad:cb:3c:cb
+          params:
+            login: admin
+            ipaddr: 192.168.24.1
+            ipport: 6231
+            passwd: password
+            lanplus: 1
+        - agent: fence_ipmilan
+          host_mac: 00:ec:ad:cb:3c:cf
+          params:
+            login: admin
+            ipaddr: 192.168.24.1
+            ipport: 6232
+            passwd: password
+            lanplus: 1
+        - agent: fence_ipmilan
+          host_mac: 00:ec:ad:cb:3c:d3
+          params:
+            login: admin
+            ipaddr: 192.168.24.1
+            ipport: 6233
+            passwd: password
+            lanplus: 1
+        - agent: fence_ipmilan
+          host_mac: 00:ec:ad:cb:3c:d7
+          params:
+            login: admin
+            ipaddr: 192.168.24.1
+            ipport: 6234
+            passwd: password
+            lanplus: 1
+
+
+Once the deployment is completed, the overcloud should show a stonith device for each compute node and one for each controller node and a GuestNode for every compute node. The expected behaviour is that if a compute node dies, it will be fenced and the VMs that were running on it will be evacuated (i.e. restarted) on another compute node.
+
+In case it is necessary to limit which VMs are to be resuscitated on another compute node, it is possible to either tag the image, the flavor or the VM with the ``evacuable`` tag. For example::
+
+  openstack image set --tag evacuable 0c305437-89eb-48bc-9997-e4e4ea77e449