Terraform/OpenStack: Enable usage of an existing router

contrib/terraform/openstack/README.md

@@ -38,6 +38,16 @@ hosts where that makes sense. You have the option of creating bastion hosts
 inside the private subnet to access the nodes there.  Alternatively, a node with
 a floating IP can be used as a jump host to nodes without.
 
+#### Using an existing router
+It is possible to use an existing router instead of creating one. To use an
+existing router set the router\_id variable to the uuid of the router you wish
+to use.
+
+For example:
+```
+router_id = "00c542e7-6f46-4535-ae95-984c7f0391a3"
+```
+
 ### Kubernetes Nodes
 You can create many different kubernetes topologies by setting the number of
 different classes of hosts. For each class there are options for allocating

contrib/terraform/openstack/kubespray.tf

@@ -12,6 +12,7 @@ module "network" {
   dns_nameservers    = "${var.dns_nameservers}"
   network_dns_domain = "${var.network_dns_domain}"
   use_neutron        = "${var.use_neutron}"
+  router_id          = "${var.router_id}"
 }
 
 module "ips" {

contrib/terraform/openstack/modules/network/main.tf

@@ -1,10 +1,15 @@
 resource "openstack_networking_router_v2" "k8s" {
   name                = "${var.cluster_name}-router"
-  count               = "${var.use_neutron}"
+  count               = "${var.use_neutron}" == 1 && "${var.router_id}" == null ? 1 : 0
   admin_state_up      = "true"
   external_network_id = "${var.external_net}"
 }
 
+data "openstack_networking_router_v2" "k8s" {
+  router_id = "${var.router_id}"
+  count     = "${var.use_neutron}" == 1 && "${var.router_id}" != null ? 1 : 0
+}
+
 resource "openstack_networking_network_v2" "k8s" {
   name           = "${var.network_name}"
   count          = "${var.use_neutron}"
@@ -23,6 +28,6 @@ resource "openstack_networking_subnet_v2" "k8s" {
 
 resource "openstack_networking_router_interface_v2" "k8s" {
   count     = "${var.use_neutron}"
-  router_id = "${openstack_networking_router_v2.k8s[count.index].id}"
+  router_id = "%{if openstack_networking_router_v2.k8s != []}${openstack_networking_router_v2.k8s[count.index].id} %{else}${var.router_id} %{endif}"
   subnet_id = "${openstack_networking_subnet_v2.k8s[count.index].id}"
 }

contrib/terraform/openstack/modules/network/outputs.tf

@@ -1,11 +1,11 @@
 output "router_id" {
-  value = "${element(concat(openstack_networking_router_v2.k8s.*.id, list("")), 0)}"
+  value = "%{if var.use_neutron == 1} ${var.router_id == null ? element(concat(openstack_networking_router_v2.k8s.*.id, [""]), 0) : var.router_id} %{else} %{endif}"
 }
 
 output "router_internal_port_id" {
-  value = "${element(concat(openstack_networking_router_interface_v2.k8s.*.id, list("")), 0)}"
+  value = "${element(concat(openstack_networking_router_interface_v2.k8s.*.id, [""]), 0)}"
 }
 
 output "subnet_id" {
-  value = "${element(concat(openstack_networking_subnet_v2.k8s.*.id, list("")), 0)}"
+  value = "${element(concat(openstack_networking_subnet_v2.k8s.*.id, [""]), 0)}"
 }

contrib/terraform/openstack/modules/network/variables.tf

@@ -13,3 +13,5 @@ variable "dns_nameservers" {
 variable "subnet_cidr" {}
 
 variable "use_neutron" {}
+
+variable "router_id" {}

contrib/terraform/openstack/variables.tf

@@ -220,3 +220,8 @@ variable "use_access_ip" {
 variable "use_server_groups" {
   default = false
 }
+
+variable "router_id" {
+  description = "uuid of an externally defined router to use"
+  default     = null
+}