Merge branch 'issue-12' into 'master'

Add support for minimum Cloud Run container instances (`min_scale`)

Closes #12

See merge request !14

examples/root-example/main.tf

@@ -3,8 +3,9 @@ module "webapp" {
   source  = "git::https://gitlab.developers.cam.ac.uk/uis/devops/infra/terraform/gcp-cloud-run-app.git"
   project = var.project
 
-  cloud_run_region = "europe-west1"
+  cloud_run_region = "europe-west2"
   max_scale        = 20
+  min_scale        = 2
 
   sql_instance_connection_name = var.sql_instance_connection_name
 }

main.tf

@@ -36,6 +36,9 @@ resource "google_cloud_run_service" "webapp" {
           # count for the Cloud SQL instance.
           "autoscaling.knative.dev/maxScale" = var.max_scale
 
+          # Minim number of instances.
+          "autoscaling.knative.dev/minScale" = var.min_scale
+
           # As mentioned at https://www.terraform.io/docs/configuration/resources.html#ignore_changes
           # placeholders need to be created as the adding the key to the map is
           # considered a change and not ignored by ignore_changes

variables.tf

@@ -29,6 +29,17 @@ variable "environment_variables" {
   default     = {}
 }
 
+variable "min_scale" {
+  description = <<EOI
+Minimum number of auto-scaled instances. Defaults to 0, thus, the container will stop
+if it doesn't receive requests for a period of time and the following request will make
+the container start from cold.
+This should be carefully considered for containers that take a significant amount of
+time starting from cold.
+EOI
+  default     = 0
+}
+
 variable "max_scale" {
   description = "Maximum number of auto-scaled instances. For a container with N-workers, maxScale should be less than 1/N of the maximum connection count for the Cloud SQL instance."
 }