diff --git a/05-osm-usage.md b/05-osm-usage.md
index dd05328a93d2db19cc1ffa7f698a9a0d27c18d6f..52511342e5ac5b52e916d2e77b6558257ba1d725 100644
--- a/05-osm-usage.md
+++ b/05-osm-usage.md
@@ -302,6 +302,46 @@ And they can be provided with:
 --config '{additionalParamsForVnf: [{member-vnf-index: "1", additionalParams: {touch_filename: your-value,  touch_filename2: your-value2}}]}'
 ```
 
+### Specifying an affinity-or-anti affinity group
+
+Affinity-or-anti-affinity groups may be defined in the VNF descriptor, in the `df` section, under `affinity-or-anti-affinity-group`.
+The type may be `affinity` or `anti-affinity`, and the scope must be `nfvi-node`. VDU profiles may reference one of the defined affinity-or-anti-affinity-group. Notice that, in Openstack, only one group is allowed. The following example shows a VNF with two VDU, both assigned to the same affinity-group `affinity-group-1`. Both virtual machines will be then instantiated in the same host.
+
+```yaml
+vnfd:
+  description: A basic VNF descriptor w/ two VDUs and an affinity group
+  df:
+  - id: default-df
+    instantiation-level:
+    - id: default-instantiation-level
+      vdu-level:
+      - number-of-instances: 1
+        vdu-id: affinity_basic-VM-1
+      - number-of-instances: 1
+        vdu-id: affinity_basic-VM-2
+    vdu-profile:
+    - id: affinity_basic-VM-1
+      min-number-of-instances: 1
+      affinity-or-anti-affinity-group:
+      - id: affinity-group-1
+    - id: affinity_basic-VM-2
+      min-number-of-instances: 1
+      affinity-or-anti-affinity-group:
+      - id: affinity-group-1
+    affinity-or-anti-affinity-group:
+    - id: affinity-group-1
+      type: affinity
+      scope: nfvi-node
+```
+
+An existing server-group may be passed as an instantiation parameter to be used as affinity-or-anti-affinity-group. In this case, the server-group will not be created, but reused, and will not be deleted when the Network Service instance is deleted. The following example shows the syntax
+
+```yaml
+ --config '{additionalParamsForVnf: [{member-vnf-index: affinity-basic-1, affinity-or-anti-affinity-group: [{ id: affinity-group-1, "vim-affinity-group-id": "81b82372-bbd4-48d6-b368-4d0b9d04d592"}]}]}'
+```
+
+Where the `id` of the `affinity-or-anti-affinity-group` is the one in the descriptor, and the `vim-affinity-group-id` is the guid of the existing server-group in Openstack to be used (instead of being created).
+
 ## Understanding Day-1 and Day-2 Operations
 
 VNF configuration is done in three "days":