diff --git a/functions-common b/functions-common
index 446de53..4fca80e 100644
--- a/functions-common
+++ b/functions-common
@@ -67,6 +67,45 @@
     done
 }
 
+# Update/create user clouds.yaml file.
+# clouds.yaml will have
+# - A `devstack` entry for the `demo` user for the `demo` project.
+# - A `devstack-admin` entry for the `admin` user for the `admin` project.
+# write_clouds_yaml
+function write_clouds_yaml {
+    # The location is a variable to allow for easier refactoring later to make it
+    # overridable. There is currently no usecase where doing so makes sense, so
+    # it's not currently configurable.
+    CLOUDS_YAML=~/.config/openstack/clouds.yaml
+
+    mkdir -p $(dirname $CLOUDS_YAML)
+
+    CA_CERT_ARG=''
+    if [ -f "$SSL_BUNDLE_FILE" ]; then
+        CA_CERT_ARG="--os-cacert $SSL_BUNDLE_FILE"
+    fi
+    $TOP_DIR/tools/update_clouds_yaml.py \
+        --file $CLOUDS_YAML \
+        --os-cloud devstack \
+        --os-region-name $REGION_NAME \
+        --os-identity-api-version $IDENTITY_API_VERSION \
+        $CA_CERT_ARG \
+        --os-auth-url $KEYSTONE_AUTH_URI/v$IDENTITY_API_VERSION \
+        --os-username demo \
+        --os-password $ADMIN_PASSWORD \
+        --os-project-name demo
+    $TOP_DIR/tools/update_clouds_yaml.py \
+        --file $CLOUDS_YAML \
+        --os-cloud devstack-admin \
+        --os-region-name $REGION_NAME \
+        --os-identity-api-version $IDENTITY_API_VERSION \
+        $CA_CERT_ARG \
+        --os-auth-url $KEYSTONE_AUTH_URI/v$IDENTITY_API_VERSION \
+        --os-username admin \
+        --os-password $ADMIN_PASSWORD \
+        --os-project-name admin
+}
+
 # Normalize config values to True or False
 # Accepts as False: 0 no No NO false False FALSE
 # Accepts as True: 1 yes Yes YES true True TRUE