max unavailable eq 1 script (#19)

discriminat.tf

@@ -74,6 +74,18 @@ variable "instances_per_zone" {
   default     = 1
 }
 
+variable "mig_update_policy_type" {
+  type        = string
+  description = "OPPORTUNISTIC or PROACTIVE. Set to OPPORTUNISTIC to prevent a `terraform apply` from initiating and waiting for a rolling update. This may be useful if DiscrimiNAT instances are set to use External IPs and there aren't any spare for new instances to attach to themselves (and warm up their cache) before being brought into service by the load balancer. This wouldn't be a problem if DiscrimiNAT instances are set to route through Google Cloud NAT, however. See the script `rmig-update-maxUnavailable-1.sh` to initiate a rolling update, one-by-one, if setting to OPPORTUNISTIC."
+  default     = "PROACTIVE"
+}
+
+variable "mig_target_size" {
+  type        = number
+  description = "If left unset, automatically sets to the number of zones_names * instances_per_zone."
+  default     = null
+}
+
 variable "block-project-ssh-keys" {
   type        = bool
   description = "Strongly suggested to leave this to the default, that is to NOT allow project-wide SSH keys to login into the firewall."
@@ -193,7 +205,7 @@ resource "google_compute_region_instance_group_manager" "discriminat" {
   name                      = "discriminat-${local.suffix}"
   base_instance_name        = "discriminat-${local.suffix}"
   distribution_policy_zones = local.zones
-  target_size               = length(local.zones) * var.instances_per_zone
+  target_size               = var.mig_target_size == null ? length(local.zones) * var.instances_per_zone : var.mig_target_size
 
   region  = var.region
   project = var.project_id
@@ -210,7 +222,7 @@ resource "google_compute_region_instance_group_manager" "discriminat" {
   }
 
   update_policy {
-    type                         = "PROACTIVE"
+    type                         = var.mig_update_policy_type
     instance_redistribution_type = "PROACTIVE"
     minimal_action               = "REPLACE"
     max_surge_fixed              = length(local.zones)

rmig-update-maxUnavailable-1.sh

@@ -0,0 +1,42 @@
+## set env vars
+
+export GOOGLE_CLOUD_PROJECT=foo-bar #change-me
+
+export MIG_NAME=discriminat-foo #change-me
+export MIG_EXPECTED_SIZE=3 #change-me
+export MIG_REGION=europe-west6 #change-me
+
+## env vars done
+
+# this script exists because of the following outstanding issues on gcp, where maxUnavailable cannot be set to 1
+# https://issuetracker.google.com/issues/201753226
+# https://issuetracker.google.com/issues/243973366
+
+## script follows
+
+CURRENT_SIZE=$(gcloud --format json compute instance-groups managed describe --region $MIG_REGION $MIG_NAME | jq .targetSize)
+
+if [ $CURRENT_SIZE -ne $MIG_EXPECTED_SIZE ]; then
+  echo -e "\nCURRENT SIZE $CURRENT_SIZE does not match MIG EXPECTED SIZE $MIG_EXPECTED_SIZE\n\nexiting\n" 1>&2
+  kill -INT $$
+fi
+
+echo "EXPECTED and CURRENT SIZE: $MIG_EXPECTED_SIZE"
+
+echo -e "\nPROGRESS 0/$MIG_EXPECTED_SIZE\n"
+gcloud compute instance-groups managed wait-until $MIG_NAME --stable --region $MIG_REGION
+
+for i in $(seq 1 $MIG_EXPECTED_SIZE); do
+  gcloud compute instance-groups managed resize $MIG_NAME --size $(($MIG_EXPECTED_SIZE - 1)) --region $MIG_REGION 1> /dev/null
+  echo -e "\nPROGRESS $(($i-1)).25/$MIG_EXPECTED_SIZE\n"
+  gcloud compute instance-groups managed wait-until $MIG_NAME --stable --region $MIG_REGION
+  echo -e "\nPROGRESS $(($i-1)).5/$MIG_EXPECTED_SIZE\n"
+  gcloud compute instance-groups managed resize $MIG_NAME --size $MIG_EXPECTED_SIZE --region $MIG_REGION 1> /dev/null
+  echo -e "\nPROGRESS $(($i-1)).75/$MIG_EXPECTED_SIZE\n"
+  gcloud compute instance-groups managed wait-until $MIG_NAME --stable --region $MIG_REGION
+  echo -e "\nPROGRESS $i/$MIG_EXPECTED_SIZE\n"
+done
+
+echo "FINAL SIZE: $(gcloud --format json compute instance-groups managed describe --region $MIG_REGION $MIG_NAME | jq .targetSize)"
+
+## script done