Apply changes from code review; add changelog entry

.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 +349,7 @@ func (j *Job) Register(args *structs.JobRegisterRequest, reply *structs.JobRegis
 	}
 
 	// Check if the job has changed at all
-	specChanged, err := j.specChanged(existingJob, args)
+	specChanged, err := j.multiregionSpecChanged(existingJob, args)
 	if err != nil {
 		return err
 	}
@@ -438,53 +438,6 @@ func (j *Job) Register(args *structs.JobRegisterRequest, reply *structs.JobRegis
 	return nil
 }
 
-// specChanged checks to see if the job spec has changed. If the job is multiregion,
-// it checks all regions. This handles the case of a multiregion job that has been
-// stopped in one or more regions being restarted via the run command.
-func (j *Job) specChanged(existingJob *structs.Job, args *structs.JobRegisterRequest) (bool, error) {
-	if existingJob == nil {
-		return false, nil
-	}
-
-	if existingJob.SpecChanged(args.Job) {
-		return true, nil
-	}
-
-	if !existingJob.IsMultiregion() {
-		return false, nil
-	}
-
-	// If the spec hasn't changed, but this is a multiregion job, check other regions.
-	for _, region := range existingJob.Multiregion.Regions {
-		// Copy the job so we can mutate it by region and compare it with the response.
-		incomingJob := args.Job.Copy()
-		incomingJob.Region = region.Name
-		req := &structs.JobSpecificRequest{
-			JobID: incomingJob.ID,
-			QueryOptions: structs.QueryOptions{
-				Region:    region.Name,
-				Namespace: incomingJob.Namespace,
-				AuthToken: args.AuthToken,
-			},
-		}
-		resp := structs.SingleJobResponse{}
-		j.logger.Debug("checking spec for multiregion job")
-		err := j.GetJob(req, &resp)
-		if err != nil {
-			j.logger.Error("job lookup failed", "error", err)
-			return false, err
-		}
-
-		// If the jobspec changed or is nil (purged) for that region, assume it's being re-registered
-		// and treat like a spec change.
-		if resp.Job.SpecChanged(incomingJob) || resp.Job == nil {
-			return true, nil
-		}
-	}
-
-	return false, nil
-}
-
 // propagateScalingPolicyIDs propagates scaling policy IDs from existing job
 // to updated job, or generates random IDs in new job
 func propagateScalingPolicyIDs(old, new *structs.Job) error {

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
+}