agent: Adding new CheckUpdateInterval config

command/agent/config.go

@@ -173,6 +173,14 @@ type Config struct {
 	// true, we ignore the leave, and rejoin the cluster on start.
 	RejoinAfterLeave bool `mapstructure:"rejoin_after_leave"`
 
+	// CheckUpdateInterval controls the interval on which the output of a health check
+	// is updated if there is no change to the state. For example, a check in a steady
+	// state may run every 5 second generating a unique output (timestamp, etc), forcing
+	// constant writes. This allows Consul to defer the write for some period of time,
+	// reducing the write pressure when the state is steady.
+	CheckUpdateInterval    time.Duration `mapstructure:"-"`
+	CheckUpdateIntervalRaw string        `mapstructure:"check_update_interval" json:"-"`
+
 	// AEInterval controls the anti-entropy interval. This is how often
 	// the agent attempts to reconcile it's local state with the server'
 	// representation of our state. Defaults to every 60s.
@@ -221,6 +229,7 @@ func DefaultConfig() *Config {
 			MaxStale: 5 * time.Second,
 		},
 		Protocol:            consul.ProtocolVersionMax,
+		CheckUpdateInterval: 5 * time.Minute,
 		AEInterval:          time.Minute,
 	}
 }
@@ -309,6 +318,14 @@ func DecodeConfig(r io.Reader) (*Config, error) {
 		}
 	}
 
+	if raw := result.CheckUpdateIntervalRaw; raw != "" {
+		dur, err := time.ParseDuration(raw)
+		if err != nil {
+			return nil, fmt.Errorf("CheckUpdateInterval invalid: %v", err)
+		}
+		result.CheckUpdateInterval = dur
+	}
+
 	return &result, nil
 }
 
@@ -536,6 +553,9 @@ func MergeConfig(a, b *Config) *Config {
 	if b.DNSConfig.MaxStale != 0 {
 		result.DNSConfig.MaxStale = b.DNSConfig.MaxStale
 	}
+	if b.CheckUpdateInterval != 0 {
+		result.CheckUpdateInterval = b.CheckUpdateInterval
+	}
 
 	// Copy the start join addresses
 	result.StartJoin = make([]string, 0, len(a.StartJoin)+len(b.StartJoin))

command/agent/config_test.go

@@ -324,6 +324,17 @@ func TestDecodeConfig(t *testing.T) {
 	if config.DNSConfig.ServiceTTL["web"] != 30*time.Second {
 		t.Fatalf("bad: %#v", config)
 	}
+
+	// CheckUpdateInterval
+	input = `{"check_update_interval": "10m"}`
+	config, err = DecodeConfig(bytes.NewReader([]byte(input)))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if config.CheckUpdateInterval != 10*time.Minute {
+		t.Fatalf("bad: %#v", config)
+	}
 }
 
 func TestDecodeConfig_Service(t *testing.T) {
@@ -466,6 +477,7 @@ func TestMergeConfig(t *testing.T) {
 		UiDir:               "/opt/consul-ui",
 		EnableSyslog:        true,
 		RejoinAfterLeave:    true,
+		CheckUpdateInterval: 8 * time.Minute,
 	}
 
 	c := MergeConfig(a, b)