job_endpoint: check spec for all regions

.changelog/14519.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+rpc: check for spec changes in all regions when registering multiregion jobs
+```

nomad/job_endpoint.go

@@ -349,7 +349,12 @@ func (j *Job) Register(args *structs.JobRegisterRequest, reply *structs.JobRegis
 	}
 
 	// Check if the job has changed at all
-	if existingJob == nil || existingJob.SpecChanged(args.Job) {
+	specChanged, err := j.multiregionSpecChanged(existingJob, args)
+	if err != nil {
+		return err
+	}
+
+	if existingJob == nil || specChanged {
 
 		// COMPAT(1.1.0): Remove the ServerMeetMinimumVersion check to always set args.Eval
 		// 0.12.1 introduced atomic eval job registration

nomad/job_endpoint_oss.go

@@ -38,3 +38,12 @@ func (j *Job) multiregionStop(job *structs.Job, args *structs.JobDeregisterReque
 func (j *Job) interpolateMultiregionFields(args *structs.JobPlanRequest) error {
 	return nil
 }
+
+// multiregionSpecChanged checks to see if the job spec has changed. If the job is multiregion,
+// it checks all regions to determine if any deployed jobs instances have been stopped or
+// otherwise differ from the incoming jobspec. Since multiregion jobs require coordinated
+// deployments and synchronized job versions across all regions, a change in one requires
+// redeployment of all.
+func (j *Job) multiregionSpecChanged(existingJob *structs.Job, args *structs.JobRegisterRequest) (bool, error) {
+	return existingJob.SpecChanged(args.Job), nil
+}