add autoscaling to the ecs services

terraform/modules/ecs/ecs.tf

@@ -108,5 +108,46 @@ resource "aws_ecs_service" "this" {
       }
     }
   }
+
+  lifecycle {
+    ignore_changes = [desired_count]
+  }
+
   tags = local.tags
 }
+
+
+resource "aws_appautoscaling_target" "this" {
+  for_each           = aws_ecs_service.this
+  max_capacity       = local.service_data[each.key].max_capacity
+  min_capacity       = local.service_data[each.key].min_capacity
+  resource_id        = each.value.id
+  scalable_dimension = "ecs:service:DesiredCount"
+  service_namespace  = "ecs"
+}
+
+resource "aws_appautoscaling_policy" "ecs_policy" {
+  for_each           = aws_appautoscaling_target.this
+  name               = "${local.service_data[each.key].short_name}-scaling"
+  policy_type        = "StepScaling"
+  resource_id        = each.value.resource_id
+  scalable_dimension = each.value.scalable_dimension
+  service_namespace  = each.value.service_namespace
+
+  step_scaling_policy_configuration {
+    adjustment_type         = "ChangeInCapacity"
+    cooldown                = 60
+    metric_aggregation_type = "Maximum"
+
+    step_adjustment {
+      metric_interval_lower_bound = 1.0
+      metric_interval_upper_bound = 2.0
+      scaling_adjustment          = -1
+    }
+    step_adjustment {
+      metric_interval_lower_bound = 2.0
+      metric_interval_upper_bound = 3.0
+      scaling_adjustment          = 1
+    }
+  }
+}