fix!: Change default balancing_mode to CONNECTION for backends (#148)

docs/upgrading_to_lb_internal_v7.0.md

@@ -0,0 +1,64 @@
+# Upgrading to v7.0 (from v6.x)
+
+The v7.0 release is a backwards incompatible release.
+
+# balancing_mode for backends
+
+The newest version of `google_compute_region_backend_service` requires a `balancing_mode` be set for backends. Therefore a default `balancing_mode` of `CONNECTION` is used in the dynamic `backend` block in v7.0 of this module. The full list of balancing modes is available in the [documentation](https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/compute_backend_service#balancing_mode).
+
+## Upgrade Guidance
+
+In this example, `balancing_mode` is *not* provided in the `backends` block. Therefore, it will default to `CONNECTION`.
+
+```hcl
+module "gce_ilb" {
+  source       = "GoogleCloudPlatform/lb-internal/google"
+  version      = ">= 4.4.0"
+  project      = var.project_id
+  region       = var.region
+  name         = "tf-ilb"
+  network      = "testnetwork"
+  subnetwork   = "testsubnet"
+  ports        = ["xxxx"]
+  health_check = local.health_check
+  source_tags  = ["xxxxxx"]
+  target_tags  = ["xxxxxx"]
+  backends = [
+    for x in google_compute_instance_group.test_ig[*] : {
+      group          = x.id
+      description    = ""
+      failover       = false
+    }
+  ]
+  create_backend_firewall      = "true"
+  create_health_check_firewall = "true"
+}
+```
+
+This is an example where the `balancing_mode` is explicitly provided:
+
+```hcl
+module "gce_ilb" {
+  source       = "GoogleCloudPlatform/lb-internal/google"
+  version      = ">= 4.4.0"
+  project      = var.project_id
+  region       = var.region
+  name         = "tf-ilb"
+  network      = "testnetwork"
+  subnetwork   = "testsubnet"
+  ports        = ["xxxx"]
+  health_check = local.health_check
+  source_tags  = ["xxxxxx"]
+  target_tags  = ["xxxxxx"]
+  backends = [
+    for x in google_compute_instance_group.test_ig[*] : {
+      group          = x.id
+      description    = ""
+      failover       = false
+      balancing_mode = "CONNECTION"
+    }
+  ]
+  create_backend_firewall      = "true"
+  create_health_check_firewall = "true"
+}
+```

main.tf

@@ -58,12 +58,14 @@ resource "google_compute_region_backend_service" "default" {
   # Do not try to add timeout_sec, as it is has no impact. See https://github.com/terraform-google-modules/terraform-google-lb-internal/issues/53#issuecomment-893427675
   connection_draining_timeout_sec = var.connection_draining_timeout_sec
   session_affinity                = var.session_affinity
+
   dynamic "backend" {
     for_each = var.backends
     content {
-      group       = lookup(backend.value, "group", null)
-      description = lookup(backend.value, "description", null)
-      failover    = lookup(backend.value, "failover", null)
+      group          = lookup(backend.value, "group", null)
+      description    = lookup(backend.value, "description", null)
+      failover       = lookup(backend.value, "failover", null)
+      balancing_mode = lookup(backend.value, "balancing_mode", "CONNECTION")
     }
   }
   health_checks = concat(google_compute_health_check.tcp[*].self_link, google_compute_health_check.http[*].self_link, google_compute_health_check.https[*].self_link)