Reaping failed evaluations creates follow up eval

Create a follow up evaluation when reaping failed evaluations. This
ensures that a job will still make eventual progress.

nomad/leader.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"math/rand"
 	"net"
 	"time"
 
@@ -19,6 +20,15 @@ const (
 	// unblocked to re-enter the scheduler. A failed evaluation occurs under
 	// high contention when the schedulers plan does not make progress.
 	failedEvalUnblockInterval = 1 * time.Minute
+
+	// failedEvalFollowUpBaseLineWait is the minimum time waited before retrying
+	// a failed evaluation.
+	failedEvalFollowUpBaseLineWait = 1 * time.Minute
+
+	// failedEvalFollowUpWaitRange defines the the range of additional time from
+	// the minimum in which to wait before retrying a failed evaluation. A value
+	// from this range should be selected using a uniform distribution.
+	failedEvalFollowUpWaitRange = 9 * time.Minute
 )
 
 // monitorLeadership is used to monitor if we acquire or lose our role
@@ -392,9 +402,16 @@ func (s *Server) reapFailedEvaluations(stopCh chan struct{}) {
 			newEval.StatusDescription = fmt.Sprintf("evaluation reached delivery limit (%d)", s.config.EvalDeliveryLimit)
 			s.logger.Printf("[WARN] nomad: eval %#v reached delivery limit, marking as failed", newEval)
 
+			// Create a follow-up evaluation that will be used to retry the
+			// scheduling for the job after the cluster is hopefully more stable
+			// due to the fairly large backoff.
+			followupEvalWait := failedEvalFollowUpBaseLineWait +
+				time.Duration(rand.Int63n(int64(failedEvalFollowUpWaitRange)))
+			followupEval := eval.CreateFailedFollowUpEval(followupEvalWait)
+
 			// Update via Raft
 			req := structs.EvalUpdateRequest{
-				Evals: []*structs.Evaluation{newEval},
+				Evals: []*structs.Evaluation{newEval, followupEval},
 			}
 			if _, _, err := s.raftApply(structs.EvalUpdateRequestType, &req); err != nil {
 				s.logger.Printf("[ERR] nomad: failed to update failed eval %#v: %v", newEval, err)

nomad/leader_test.go

@@ -508,15 +508,53 @@ func TestLeader_ReapFailedEval(t *testing.T) {
 	}
 	s1.evalBroker.Nack(out.ID, token)
 
-	// Wait updated evaluation
+	// Wait for an updated and followup evaluation
 	state := s1.fsm.State()
 	testutil.WaitForResult(func() (bool, error) {
 		ws := memdb.NewWatchSet()
 		out, err := state.EvalByID(ws, eval.ID)
 		if err != nil {
 			return false, err
 		}
-		return out != nil && out.Status == structs.EvalStatusFailed, nil
+		if out == nil {
+			return false, fmt.Errorf("expect original evaluation to exist")
+		}
+		if out.Status != structs.EvalStatusFailed {
+			return false, fmt.Errorf("got status %v; want %v", out.Status, structs.EvalStatusFailed)
+		}
+
+		// See if there is a followup
+		evals, err := state.EvalsByJob(ws, eval.JobID)
+		if err != nil {
+			return false, err
+		}
+
+		if l := len(evals); l != 2 {
+			return false, fmt.Errorf("got %d evals, want 2", l)
+		}
+
+		for _, e := range evals {
+			if e.ID == eval.ID {
+				continue
+			}
+
+			if e.Status != structs.EvalStatusPending {
+				return false, fmt.Errorf("follow up eval has status %v; want %v",
+					e.Status, structs.EvalStatusPending)
+			}
+
+			if e.Wait < failedEvalFollowUpBaseLineWait ||
+				e.Wait > failedEvalFollowUpBaseLineWait+failedEvalFollowUpWaitRange {
+				return false, fmt.Errorf("bad wait: %v", e.Wait)
+			}
+
+			if e.TriggeredBy != structs.EvalTriggerFailedFollowUp {
+				return false, fmt.Errorf("follow up eval TriggeredBy %v; want %v",
+					e.TriggeredBy, structs.EvalTriggerFailedFollowUp)
+			}
+		}
+
+		return true, nil
 	}, func(err error) {
 		t.Fatalf("err: %v", err)
 	})

nomad/structs/structs.go

@@ -3736,13 +3736,14 @@ const (
 )
 
 const (
-	EvalTriggerJobRegister   = "job-register"
-	EvalTriggerJobDeregister = "job-deregister"
-	EvalTriggerPeriodicJob   = "periodic-job"
-	EvalTriggerNodeUpdate    = "node-update"
-	EvalTriggerScheduled     = "scheduled"
-	EvalTriggerRollingUpdate = "rolling-update"
-	EvalTriggerMaxPlans      = "max-plan-attempts"
+	EvalTriggerJobRegister    = "job-register"
+	EvalTriggerJobDeregister  = "job-deregister"
+	EvalTriggerPeriodicJob    = "periodic-job"
+	EvalTriggerNodeUpdate     = "node-update"
+	EvalTriggerScheduled      = "scheduled"
+	EvalTriggerRollingUpdate  = "rolling-update"
+	EvalTriggerFailedFollowUp = "failed-eval-follow-up"
+	EvalTriggerMaxPlans       = "max-plan-attempts"
 )
 
 const (
@@ -3985,6 +3986,23 @@ func (e *Evaluation) CreateBlockedEval(classEligibility map[string]bool, escaped
 	}
 }
 
+// CreateFailedFollowUpEval creates a follow up evaluation when the current one
+// has been marked as failed becasue it has hit the delivery limit and will not
+// be retried by the eval_broker.
+func (e *Evaluation) CreateFailedFollowUpEval(wait time.Duration) *Evaluation {
+	return &Evaluation{
+		ID:             GenerateUUID(),
+		Priority:       e.Priority,
+		Type:           e.Type,
+		TriggeredBy:    EvalTriggerFailedFollowUp,
+		JobID:          e.JobID,
+		JobModifyIndex: e.JobModifyIndex,
+		Status:         EvalStatusPending,
+		Wait:           wait,
+		PreviousEval:   e.ID,
+	}
+}
+
 // Plan is used to submit a commit plan for task allocations. These
 // are submitted to the leader which verifies that resources have
 // not been overcommitted before admiting the plan.