From ba3544c50c7ad5bc4e4f773671093b0115f227d7 Mon Sep 17 00:00:00 2001
From: James Rasell <jrasell@users.noreply.github.com>
Date: Mon, 8 Jan 2024 14:14:00 +0000
Subject: [PATCH] backport of commit fbea8d105146536214397952e1f5eb28e9e1e0e0

---
 .changelog/19652.txt          |  3 +++
 nomad/structs/structs.go      |  2 +-
 nomad/structs/structs_test.go | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 .changelog/19652.txt

diff --git a/.changelog/19652.txt b/.changelog/19652.txt
new file mode 100644
index 00000000000..10dfce05226
--- /dev/null
+++ b/.changelog/19652.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+server: Fix panic when validating non-service reschedule block
+```
diff --git a/nomad/structs/structs.go b/nomad/structs/structs.go
index 8d6613605e3..334698c594a 100644
--- a/nomad/structs/structs.go
+++ b/nomad/structs/structs.go
@@ -4674,7 +4674,7 @@ func (j *Job) Validate() error {
 		}
 
 		if tg.MaxClientDisconnect != nil &&
-			tg.ReschedulePolicy.Attempts > 0 &&
+			(tg.ReschedulePolicy != nil && tg.ReschedulePolicy.Attempts > 0) &&
 			tg.PreventRescheduleOnLost {
 			err := fmt.Errorf("max_client_disconnect and prevent_reschedule_on_lost cannot be enabled when rechedule.attempts > 0")
 			mErr.Errors = append(mErr.Errors, err)
diff --git a/nomad/structs/structs_test.go b/nomad/structs/structs_test.go
index 5372ee5fe35..0961f845b76 100644
--- a/nomad/structs/structs_test.go
+++ b/nomad/structs/structs_test.go
@@ -470,6 +470,39 @@ func TestJob_ValidateNullChar(t *testing.T) {
 	assert.Error(job.Validate(), "null character in task name should not validate")
 }
 
+func TestJob_Validate_DisconnectRescheduleLost(t *testing.T) {
+	ci.Parallel(t)
+
+	// Craft our speciality jobspec to test this particular use-case.
+	testDisconnectRescheduleLostJob := &Job{
+		ID:     "gh19644",
+		Name:   "gh19644",
+		Region: "global",
+		Type:   JobTypeSystem,
+		TaskGroups: []*TaskGroup{
+			{
+				Name:                    "cache",
+				MaxClientDisconnect:     pointer.Of(1 * time.Hour),
+				PreventRescheduleOnLost: true,
+				Tasks: []*Task{
+					{
+						Name:   "redis",
+						Driver: "docker",
+						Config: map[string]interface{}{
+							"image": "redis:7",
+						},
+						LogConfig: DefaultLogConfig(),
+					},
+				},
+			},
+		},
+	}
+
+	testDisconnectRescheduleLostJob.Canonicalize()
+
+	must.NoError(t, testDisconnectRescheduleLostJob.Validate())
+}
+
 func TestJob_Warnings(t *testing.T) {
 	ci.Parallel(t)