Intermediate migration configuration

- Configuration to be deployed when the target database is ready for
  switchover as detailed in terraform/app/modules/dms/README.md

Author: TheOneFromNorway

terraform/account/resources/github_actions_dms_policy.json

@@ -0,0 +1,28 @@
+{
+  "Version": "2012-10-17",
+  "Statement": [
+    {
+      "Sid": "Statement1",
+      "Effect": "Allow",
+      "Action": [
+        "dms:CreateDataMigration",
+        "dms:CreateEndpoint",
+        "dms:CreateReplicationConfig",
+        "dms:CreateReplicationInstance",
+        "dms:CreateReplicationSubnetGroup",
+        "dms:CreateReplicationTask",
+        "dms:DeleteEndpoint",
+        "dms:DeleteReplicationConfig",
+        "dms:DeleteReplicationInstance",
+        "dms:DeleteReplicationTask",
+        "dms:DeleteReplicationSubnetGroup",
+        "dms:ModifyEndpoint",
+        "dms:ModifyReplicationConfig",
+        "dms:ModifyReplicationTask",
+        "dms:ModifyReplicationInstance",
+        "dms:ModifyReplicationSubnetGroup"
+      ],
+      "Resource": ["*"]
+    }
+  ]
+}

terraform/app/outputs.tf

@@ -36,5 +36,5 @@ output "ecs_variables" {
 
 output "db_secret_arn" {
   description = "The ARN of the secret containing the DB credentials."
-  value       = var.db_secret_arn == null ? aws_rds_cluster.aurora_cluster.master_user_secret[0].secret_arn : var.db_secret_arn
+  value       = aws_rds_cluster.core.master_user_secret[0].secret_arn
 }

terraform/app/rds.tf

@@ -116,14 +116,9 @@ resource "aws_rds_cluster_parameter_group" "migration_target" {
 
   parameter {
     name         = "session_replication_role"
-    value        = "replica"
+    value        = "origin"
     apply_method = "immediate"
   }
-  parameter {
-    name         = "max_wal_senders"
-    value        = 20
-    apply_method = "pending-reboot"
-  }
 }
 
 resource "aws_rds_cluster" "core" {

terraform/app/variables.tf

@@ -180,11 +180,11 @@ locals {
   task_envs = [
     {
       name  = "DB_HOST"
-      value = aws_rds_cluster.aurora_cluster.endpoint
+      value = aws_rds_cluster.core.endpoint
     },
     {
       name  = "DB_NAME"
-      value = aws_rds_cluster.aurora_cluster.database_name
+      value = aws_rds_cluster.core.database_name
     },
     {
       name  = "RAILS_ENV"
@@ -217,8 +217,8 @@ locals {
   ]
   task_secrets = concat([
     {
-      name      = var.db_secret_arn == null ? "DB_CREDENTIALS" : "DB_SECRET"
-      valueFrom = var.db_secret_arn == null ? aws_rds_cluster.aurora_cluster.master_user_secret[0].secret_arn : var.db_secret_arn
+      name      = "DB_CREDENTIALS"
+      valueFrom = aws_rds_cluster.core.master_user_secret[0].secret_arn
     },
     {
       name      = "RAILS_MASTER_KEY"