handle FSM.Apply errors in raftApply (#16287)

The signature of the `raftApply` function requires that the caller unwrap the
first returned value (the response from `FSM.Apply`) to see if it's an
error. This puts the burden on the caller to remember to check two different
places for errors, and we've done so inconsistently.

Update `raftApply` to do the unwrapping for us and return any `FSM.Apply` error
as the error value. Similar work was done in Consul in
hashicorp/consul#9991. This eliminates some boilerplate
and surfaces a few minor bugs in the process:

* job deregistrations of already-GC'd jobs were still emitting evals
* reconcile job summaries does not return scheduler errors
* node updates did not report errors associated with inconsistent service
  discovery or CSI plugin states

Note that although _most_ of the `FSM.Apply` functions return only errors (which
makes it tempting to remove the first return value entirely), there are few that
return `bool` for some reason and Variables relies on the response value for
proper CAS checking.

.changelog/16287.txt

@@ -0,0 +1,11 @@
+```release-note:bug
+server: Fixed a bug where deregistering a job that was already garbage collected would create a new evaluation
+```
+
+```release-note:bug
+server: Fixed a bug where the `system reconcile summaries` command and API would not return any scheduler-related errors
+```
+
+```release-note:bug
+server: Fixed a bug where node updates that produced errors from service discovery or CSI plugin updates were not logged
+```

api/jobs_test.go

@@ -1554,7 +1554,7 @@ func TestJobs_Deregister(t *testing.T) {
 	must.NoError(t, err)
 	assertWriteMeta(t, wm)
 
-	// Attempting delete on non-existing job returns an error
+	// Attempting delete on non-existing job does not return an error
 	_, _, err = jobs.Deregister("nope", false, nil)
 	must.NoError(t, err)
 

api/nodes_test.go

@@ -13,6 +13,7 @@ import (
 )
 
 func queryNodeList(t *testing.T, nodes *Nodes) ([]*NodeListStub, *QueryMeta) {
+	t.Helper()
 	var (
 		nodeListStub []*NodeListStub
 		queryMeta    *QueryMeta

nomad/acl_endpoint.go

@@ -1342,16 +1342,11 @@ func (a *ACL) UpsertRoles(
 	}
 
 	// Update via Raft.
-	out, index, err := a.srv.raftApply(structs.ACLRolesUpsertRequestType, args)
+	_, index, err := a.srv.raftApply(structs.ACLRolesUpsertRequestType, args)
 	if err != nil {
 		return err
 	}
 
-	// Check if the FSM response, which is an interface, contains an error.
-	if err, ok := out.(error); ok && err != nil {
-		return err
-	}
-
 	// Populate the response. We do a lookup against the state to pick up the
 	// proper create / modify times.
 	stateSnapshot, err = a.srv.State().Snapshot()
@@ -1413,16 +1408,11 @@ func (a *ACL) DeleteRolesByID(
 	}
 
 	// Update via Raft.
-	out, index, err := a.srv.raftApply(structs.ACLRolesDeleteByIDRequestType, args)
+	_, index, err := a.srv.raftApply(structs.ACLRolesDeleteByIDRequestType, args)
 	if err != nil {
 		return err
 	}
 
-	// Check if the FSM response, which is an interface, contains an error.
-	if err, ok := out.(error); ok && err != nil {
-		return err
-	}
-
 	// Update the index. There is no need to floor this as we are writing to
 	// state and therefore will get a non-zero index response.
 	reply.Index = index
@@ -1899,16 +1889,11 @@ func (a *ACL) UpsertAuthMethods(
 	}
 
 	// Update via Raft
-	out, index, err := a.srv.raftApply(structs.ACLAuthMethodsUpsertRequestType, args)
+	_, index, err := a.srv.raftApply(structs.ACLAuthMethodsUpsertRequestType, args)
 	if err != nil {
 		return err
 	}
 
-	// Check if the FSM response, which is an interface, contains an error.
-	if err, ok := out.(error); ok && err != nil {
-		return err
-	}
-
 	// Populate the response. We do a lookup against the state to pick up the
 	// proper create / modify times.
 	stateSnapshot, err = a.srv.State().Snapshot()
@@ -1972,16 +1957,11 @@ func (a *ACL) DeleteAuthMethods(
 	}
 
 	// Update via Raft
-	out, index, err := a.srv.raftApply(structs.ACLAuthMethodsDeleteRequestType, args)
+	_, index, err := a.srv.raftApply(structs.ACLAuthMethodsDeleteRequestType, args)
 	if err != nil {
 		return err
 	}
 
-	// Check if the FSM response, which is an interface, contains an error.
-	if err, ok := out.(error); ok && err != nil {
-		return err
-	}
-
 	// Update the index
 	reply.Index = index
 	return nil
@@ -2278,16 +2258,11 @@ func (a *ACL) UpsertBindingRules(
 	}
 
 	// Update via Raft.
-	out, index, err := a.srv.raftApply(structs.ACLBindingRulesUpsertRequestType, args)
+	_, index, err := a.srv.raftApply(structs.ACLBindingRulesUpsertRequestType, args)
 	if err != nil {
 		return err
 	}
 
-	// Check if the FSM response, which is an interface, contains an error.
-	if err, ok := out.(error); ok && err != nil {
-		return err
-	}
-
 	// Populate the response. We do a lookup against the state to pick up the
 	// proper create / modify indexes.
 	stateSnapshot, err = a.srv.State().Snapshot()
@@ -2353,16 +2328,11 @@ func (a *ACL) DeleteBindingRules(
 	}
 
 	// Update via Raft.
-	out, index, err := a.srv.raftApply(structs.ACLBindingRulesDeleteRequestType, args)
+	_, index, err := a.srv.raftApply(structs.ACLBindingRulesDeleteRequestType, args)
 	if err != nil {
 		return err
 	}
 
-	// Check if the FSM response, which is an interface, contains an error.
-	if err, ok := out.(error); ok && err != nil {
-		return err
-	}
-
 	// Update the index
 	reply.Index = index
 	return nil

nomad/csi_endpoint.go

@@ -354,14 +354,11 @@ func (v *CSIVolume) Register(args *structs.CSIVolumeRegisterRequest, reply *stru
 		}
 	}
 
-	resp, index, err := v.srv.raftApply(structs.CSIVolumeRegisterRequestType, args)
+	_, index, err := v.srv.raftApply(structs.CSIVolumeRegisterRequestType, args)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err, "method", "register")
 		return err
 	}
-	if respErr, ok := resp.(error); ok {
-		return respErr
-	}
 
 	reply.Index = index
 	v.srv.setQueryMeta(&reply.QueryMeta)
@@ -397,14 +394,11 @@ func (v *CSIVolume) Deregister(args *structs.CSIVolumeDeregisterRequest, reply *
 		return fmt.Errorf("missing volume IDs")
 	}
 
-	resp, index, err := v.srv.raftApply(structs.CSIVolumeDeregisterRequestType, args)
+	_, index, err := v.srv.raftApply(structs.CSIVolumeDeregisterRequestType, args)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err, "method", "deregister")
 		return err
 	}
-	if respErr, ok := resp.(error); ok {
-		return respErr
-	}
 
 	reply.Index = index
 	v.srv.setQueryMeta(&reply.QueryMeta)
@@ -458,14 +452,11 @@ func (v *CSIVolume) Claim(args *structs.CSIVolumeClaimRequest, reply *structs.CS
 		args.NodeID = alloc.NodeID
 	}
 
-	resp, index, err := v.srv.raftApply(structs.CSIVolumeClaimRequestType, args)
+	_, index, err := v.srv.raftApply(structs.CSIVolumeClaimRequestType, args)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err, "method", "claim")
 		return err
 	}
-	if respErr, ok := resp.(error); ok {
-		return respErr
-	}
 
 	if isNewClaim {
 		// if this is a new claim, add a Volume and PublishContext from the
@@ -931,14 +922,11 @@ func (v *CSIVolume) checkpointClaim(vol *structs.CSIVolume, claim *structs.CSIVo
 			Namespace: vol.Namespace,
 		},
 	}
-	resp, index, err := v.srv.raftApply(structs.CSIVolumeClaimRequestType, req)
+	_, index, err := v.srv.raftApply(structs.CSIVolumeClaimRequestType, req)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err)
 		return err
 	}
-	if respErr, ok := resp.(error); ok {
-		return respErr
-	}
 	vol.ModifyIndex = index
 	return nil
 }
@@ -1023,13 +1011,10 @@ func (v *CSIVolume) Create(args *structs.CSIVolumeCreateRequest, reply *structs.
 		}
 	}
 
-	resp, index, err := v.srv.raftApply(structs.CSIVolumeRegisterRequestType, regArgs)
+	_, index, err := v.srv.raftApply(structs.CSIVolumeRegisterRequestType, regArgs)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err, "method", "register")
-		return err
-	}
-	if respErr, ok := resp.(error); ok {
-		multierror.Append(&mErr, respErr)
+		multierror.Append(&mErr, err)
 	}
 
 	err = mErr.ErrorOrNil()
@@ -1123,14 +1108,11 @@ func (v *CSIVolume) Delete(args *structs.CSIVolumeDeleteRequest, reply *structs.
 		VolumeIDs:    args.VolumeIDs,
 		WriteRequest: args.WriteRequest,
 	}
-	resp, index, err := v.srv.raftApply(structs.CSIVolumeDeregisterRequestType, deregArgs)
+	_, index, err := v.srv.raftApply(structs.CSIVolumeDeregisterRequestType, deregArgs)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err, "method", "deregister")
 		return err
 	}
-	if respErr, ok := resp.(error); ok {
-		return respErr
-	}
 
 	reply.Index = index
 	v.srv.setQueryMeta(&reply.QueryMeta)
@@ -1611,16 +1593,12 @@ func (v *CSIPlugin) Delete(args *structs.CSIPluginDeleteRequest, reply *structs.
 		return fmt.Errorf("missing plugin ID")
 	}
 
-	resp, index, err := v.srv.raftApply(structs.CSIPluginDeleteRequestType, args)
+	_, index, err := v.srv.raftApply(structs.CSIPluginDeleteRequestType, args)
 	if err != nil {
 		v.logger.Error("csi raft apply failed", "error", err, "method", "delete")
 		return err
 	}
 
-	if respErr, ok := resp.(error); ok {
-		return respErr
-	}
-
 	reply.Index = index
 	v.srv.setQueryMeta(&reply.QueryMeta)
 	return nil

nomad/drainer_shims.go

@@ -28,8 +28,8 @@ func (d drainerShim) NodesDrainComplete(nodes []string, event *structs.NodeEvent
 		}
 	}
 
-	resp, index, err := d.s.raftApply(structs.BatchNodeUpdateDrainRequestType, args)
-	return d.convertApplyErrors(resp, index, err)
+	_, index, err := d.s.raftApply(structs.BatchNodeUpdateDrainRequestType, args)
+	return index, err
 }
 
 func (d drainerShim) AllocUpdateDesiredTransition(allocs map[string]*structs.DesiredTransition, evals []*structs.Evaluation) (uint64, error) {
@@ -38,19 +38,6 @@ func (d drainerShim) AllocUpdateDesiredTransition(allocs map[string]*structs.Des
 		Evals:        evals,
 		WriteRequest: structs.WriteRequest{Region: d.s.config.Region},
 	}
-	resp, index, err := d.s.raftApply(structs.AllocUpdateDesiredTransitionRequestType, args)
-	return d.convertApplyErrors(resp, index, err)
-}
-
-// convertApplyErrors parses the results of a raftApply and returns the index at
-// which it was applied and any error that occurred. Raft Apply returns two
-// separate errors, Raft library errors and user returned errors from the FSM.
-// This helper, joins the errors by inspecting the applyResponse for an error.
-func (d drainerShim) convertApplyErrors(applyResp interface{}, index uint64, err error) (uint64, error) {
-	if applyResp != nil {
-		if fsmErr, ok := applyResp.(error); ok && fsmErr != nil {
-			return index, fsmErr
-		}
-	}
+	_, index, err := d.s.raftApply(structs.AllocUpdateDesiredTransitionRequestType, args)
 	return index, err
 }

nomad/job_endpoint.go

@@ -376,13 +376,9 @@ func (j *Job) Register(args *structs.JobRegisterRequest, reply *structs.JobRegis
 		args.Deployment = j.multiregionCreateDeployment(job, eval)
 
 		// Commit this update via Raft
-		fsmErr, index, err := j.srv.raftApply(structs.JobRegisterRequestType, args)
-		if err, ok := fsmErr.(error); ok && err != nil {
-			j.logger.Error("registering job failed", "error", err, "fsm", true)
-			return err
-		}
+		_, index, err := j.srv.raftApply(structs.JobRegisterRequestType, args)
 		if err != nil {
-			j.logger.Error("registering job failed", "error", err, "raft", true)
+			j.logger.Error("registering job failed", "error", err)
 			return err
 		}
 
@@ -850,6 +846,9 @@ func (j *Job) Deregister(args *structs.JobDeregisterRequest, reply *structs.JobD
 	if err != nil {
 		return err
 	}
+	if job == nil {
+		return nil
+	}
 
 	var eval *structs.Evaluation
 
@@ -858,7 +857,7 @@ func (j *Job) Deregister(args *structs.JobDeregisterRequest, reply *structs.JobD
 	now := time.Now().UnixNano()
 
 	// If the job is periodic or parameterized, we don't create an eval.
-	if job == nil || !(job.IsPeriodic() || job.IsParameterized()) {
+	if !(job.IsPeriodic() || job.IsParameterized()) {
 
 		// The evaluation priority is determined by several factors. It
 		// defaults to the job default priority and is overridden by the
@@ -867,7 +866,7 @@ func (j *Job) Deregister(args *structs.JobDeregisterRequest, reply *structs.JobD
 		// If the user supplied an eval priority override, we subsequently
 		// use this.
 		priority := structs.JobDefaultPriority
-		if job != nil {
+		if job.Priority > 0 {
 			priority = job.Priority
 		}
 		if args.EvalPriority > 0 {
@@ -2027,13 +2026,9 @@ func (j *Job) Dispatch(args *structs.JobDispatchRequest, reply *structs.JobDispa
 	}
 
 	// Commit this update via Raft
-	fsmErr, jobCreateIndex, err := j.srv.raftApply(structs.JobRegisterRequestType, regReq)
-	if err, ok := fsmErr.(error); ok && err != nil {
-		j.logger.Error("dispatched job register failed", "error", err, "fsm", true)
-		return err
-	}
+	_, jobCreateIndex, err := j.srv.raftApply(structs.JobRegisterRequestType, regReq)
 	if err != nil {
-		j.logger.Error("dispatched job register failed", "error", err, "raft", true)
+		j.logger.Error("dispatched job register failed", "error")
 		return err
 	}