Add ability to mark instances as absent (#1731)

* Mark hosts as absent on backend

* Revert changes to cluster

* Add tests and rework implementation

* Abstract repeated code into a private helper function

* Reordering tests

* Move test for initial conditions into pre-existing tests

* Separate database/application instance tests

* Refactor `update_instance()` to use pattern-matching

* Revert formatting

* Use namespaced `Kernel.struct()`

* Renaming

* Remove `SapSystem` namespace

* Remove redundant initialisation of default fields

* Renaming

lib/trento/application/integration/discovery/policies/sap_system_policy.ex

@@ -8,6 +8,8 @@ defmodule Trento.Integration.Discovery.SapSystemPolicy do
   alias Trento.Domain.Commands.{
     DeregisterApplicationInstance,
     DeregisterDatabaseInstance,
+    MarkApplicationInstanceAbsent,
+    MarkDatabaseInstanceAbsent,
     RegisterApplicationInstance,
     RegisterDatabaseInstance
   }
@@ -146,21 +148,19 @@ defmodule Trento.Integration.Discovery.SapSystemPolicy do
   defp build_deregister_instances_commands(current_instances) do
     Enum.map(current_instances, fn
       %ApplicationInstanceReadModel{} = instance ->
-        DeregisterApplicationInstance.new!(%{
-          sid: instance.sid,
+        MarkApplicationInstanceAbsent.new!(%{
           host_id: instance.host_id,
           instance_number: instance.instance_number,
           sap_system_id: instance.sap_system_id,
-          deregistered_at: DateTime.utc_now()
+          absent_at: DateTime.utc_now()
         })
 
       %DatabaseInstanceReadModel{} = instance ->
-        DeregisterDatabaseInstance.new!(%{
-          sid: instance.sid,
+        MarkDatabaseInstanceAbsent.new!(%{
           host_id: instance.host_id,
           instance_number: instance.instance_number,
           sap_system_id: instance.sap_system_id,
-          deregistered_at: DateTime.utc_now()
+          absent_at: DateTime.utc_now()
         })
     end)
   end

lib/trento/domain/sap_system/commands/mark_application_instance_absent.ex

@@ -0,0 +1,15 @@
+defmodule Trento.Domain.Commands.MarkApplicationInstanceAbsent do
+  @moduledoc """
+  Mark an application instance as absent
+  """
+  @required_fields :all
+
+  use Trento.Command
+
+  defcommand do
+    field :instance_number, :string
+    field :host_id, Ecto.UUID
+    field :sap_system_id, Ecto.UUID
+    field :absent_at, :utc_datetime_usec
+  end
+end

lib/trento/domain/sap_system/commands/mark_database_instance_absent.ex

@@ -0,0 +1,15 @@
+defmodule Trento.Domain.Commands.MarkDatabaseInstanceAbsent do
+  @moduledoc """
+  Mark a database instance as absent
+  """
+  @required_fields :all
+
+  use Trento.Command
+
+  defcommand do
+    field :instance_number, :string
+    field :host_id, Ecto.UUID
+    field :sap_system_id, Ecto.UUID
+    field :absent_at, :utc_datetime_usec
+  end
+end

lib/trento/domain/sap_system/events/application_instance_marked_absent.ex

@@ -0,0 +1,14 @@
+defmodule Trento.Domain.Events.ApplicationInstanceMarkedAbsent do
+  @moduledoc """
+  This event is emitted when an application instance is marked as absent from the SAP system.
+  """
+
+  use Trento.Event
+
+  defevent do
+    field :instance_number, :string
+    field :host_id, Ecto.UUID
+    field :sap_system_id, Ecto.UUID
+    field :absent_at, :utc_datetime_usec
+  end
+end

lib/trento/domain/sap_system/events/application_instance_marked_present.ex

@@ -0,0 +1,13 @@
+defmodule Trento.Domain.Events.ApplicationInstanceMarkedPresent do
+  @moduledoc """
+  This event is emitted when an application instance is marked as present in the SAP system.
+  """
+
+  use Trento.Event
+
+  defevent do
+    field :instance_number, :string
+    field :host_id, Ecto.UUID
+    field :sap_system_id, Ecto.UUID
+  end
+end

lib/trento/domain/sap_system/events/database_instance_marked_absent.ex

@@ -0,0 +1,14 @@
+defmodule Trento.Domain.Events.DatabaseInstanceMarkedAbsent do
+  @moduledoc """
+  This event is emitted when a database instance is marked as absent from the SAP system.
+  """
+
+  use Trento.Event
+
+  defevent do
+    field :instance_number, :string
+    field :host_id, Ecto.UUID
+    field :sap_system_id, Ecto.UUID
+    field :absent_at, :utc_datetime_usec
+  end
+end

lib/trento/domain/sap_system/events/database_instance_marked_present.ex

@@ -0,0 +1,13 @@
+defmodule Trento.Domain.Events.DatabaseInstanceMarkedPresent do
+  @moduledoc """
+  This event is emitted when a database instance is marked as present in the SAP system.
+  """
+
+  use Trento.Event
+
+  defevent do
+    field :instance_number, :string
+    field :host_id, Ecto.UUID
+    field :sap_system_id, Ecto.UUID
+  end
+end

lib/trento/domain/sap_system/instance.ex

@@ -17,5 +17,6 @@ defmodule Trento.Domain.SapSystem.Instance do
     field :health, Ecto.Enum, values: Health.values()
     field :system_replication, :string
     field :system_replication_status, :string
+    field :absent_at, :utc_datetime_usec
   end
 end