From 5155f2c8eb775ddb6fe6ba2a79e86ce313b25376 Mon Sep 17 00:00:00 2001
From: Armon Dadgar <armon.dadgar@gmail.com>
Date: Sat, 29 Aug 2015 14:14:19 -0700
Subject: [PATCH] nomad: parameterize heartbeat configuration

---
 nomad/config.go    | 53 +++++++++++++++++++++++++++++++++-------------
 nomad/heartbeat.go | 26 ++++-------------------
 2 files changed, 42 insertions(+), 37 deletions(-)

diff --git a/nomad/config.go b/nomad/config.go
index cfc5d5b95..767fb4e13 100644
--- a/nomad/config.go
+++ b/nomad/config.go
@@ -146,6 +146,25 @@ type Config struct {
 	// process an evaluation. This is used so that an eval that will never
 	// complete eventually fails out of the system.
 	EvalDeliveryLimit int
+
+	// MinHeartbeatTTL is the minimum time between heartbeats.
+	// This is used as a floor to prevent excessive updates.
+	MinHeartbeatTTL time.Duration
+
+	// MaxHeartbeatsPerSecond is the maximum target rate of heartbeats
+	// being processed per second. This allows the TTL to be increased
+	// to meet the target rate.
+	MaxHeartbeatsPerSecond float64
+
+	// HeartbeatGrace is the additional time given as a grace period
+	// beyond the TTL to account for network and processing delays
+	// as well as clock skew.
+	HeartbeatGrace time.Duration
+
+	// FailoverHeartbeatTTL is the TTL applied to heartbeats after
+	// a new leader is elected, since we no longer know the status
+	// of all the heartbeats.
+	FailoverHeartbeatTTL time.Duration
 }
 
 // CheckVersion is used to check if the ProtocolVersion is valid
@@ -168,21 +187,25 @@ func DefaultConfig() *Config {
 	}
 
 	c := &Config{
-		Region:            DefaultRegion,
-		Datacenter:        DefaultDC,
-		NodeName:          hostname,
-		ProtocolVersion:   ProtocolVersionMax,
-		RaftConfig:        raft.DefaultConfig(),
-		RaftTimeout:       10 * time.Second,
-		RPCAddr:           DefaultRPCAddr,
-		SerfConfig:        serf.DefaultConfig(),
-		NumSchedulers:     1,
-		ServerAddress:     []string{"nomad.service.consul:4647"},
-		ReconcileInterval: 60 * time.Second,
-		EvalGCInterval:    60 * time.Second,
-		EvalGCThreshold:   1 * time.Hour,
-		EvalNackTimeout:   60 * time.Second,
-		EvalDeliveryLimit: 3,
+		Region:                 DefaultRegion,
+		Datacenter:             DefaultDC,
+		NodeName:               hostname,
+		ProtocolVersion:        ProtocolVersionMax,
+		RaftConfig:             raft.DefaultConfig(),
+		RaftTimeout:            10 * time.Second,
+		RPCAddr:                DefaultRPCAddr,
+		SerfConfig:             serf.DefaultConfig(),
+		NumSchedulers:          1,
+		ServerAddress:          []string{"nomad.service.consul:4647"},
+		ReconcileInterval:      60 * time.Second,
+		EvalGCInterval:         60 * time.Second,
+		EvalGCThreshold:        1 * time.Hour,
+		EvalNackTimeout:        60 * time.Second,
+		EvalDeliveryLimit:      3,
+		MinHeartbeatTTL:        10 * time.Second,
+		MaxHeartbeatsPerSecond: 50.0,
+		HeartbeatGrace:         10 * time.Second,
+		FailoverHeartbeatTTL:   300 * time.Second,
 	}
 
 	// Enable all known schedulers by default
diff --git a/nomad/heartbeat.go b/nomad/heartbeat.go
index e52c4ad21..1fdf91f4d 100644
--- a/nomad/heartbeat.go
+++ b/nomad/heartbeat.go
@@ -7,25 +7,6 @@ import (
 	"github.com/hashicorp/nomad/nomad/structs"
 )
 
-const (
-	// defaultHeartbeatTTL is the TTL value used for heartbeats
-	// when they are first initialized. This should be longer than
-	// the usual TTL since clients are switching to a new leader.
-	defaultHeartbeatTTL = 300 * time.Second
-
-	// minHeartbeatTTL is the minimum heartbeat interval.
-	minHeartbeatTTL = 10 * time.Second
-
-	// maxHeartbeatsPerSecond is the targeted maximum rate of heartbeats.
-	// As the cluster size grows, we simply increase the heartbeat TTL
-	// to approach this value.
-	maxHeartbeatsPerSecond = 50.0
-
-	// heartbeatGrace is the additional time given to the TTL period
-	// as a grace. This is to account for various network and processing delays.
-	heartbeatGrace = 10 * time.Second
-)
-
 // initializeHeartbeatTimers is used when a leader is newly elected to create
 // a new map to track heartbeat expiration and to reset all the timers from
 // the previously known set of timers.
@@ -55,7 +36,7 @@ func (s *Server) initializeHeartbeatTimers() error {
 		if node.TerminalStatus() {
 			continue
 		}
-		s.resetHeartbeatTimerLocked(node.ID, defaultHeartbeatTTL)
+		s.resetHeartbeatTimerLocked(node.ID, s.config.FailoverHeartbeatTTL)
 	}
 	return nil
 }
@@ -68,11 +49,12 @@ func (s *Server) resetHeartbeatTimer(id string) (time.Duration, error) {
 
 	// Compute the target TTL value
 	n := len(s.heartbeatTimers)
-	ttl := rateScaledInterval(maxHeartbeatsPerSecond, minHeartbeatTTL, n)
+	ttl := rateScaledInterval(s.config.MaxHeartbeatsPerSecond,
+		s.config.MinHeartbeatTTL, n)
 	ttl += randomStagger(ttl)
 
 	// Reset the TTL
-	s.resetHeartbeatTimerLocked(id, ttl+heartbeatGrace)
+	s.resetHeartbeatTimerLocked(id, ttl+s.config.HeartbeatGrace)
 	return ttl, nil
 }