Adds a max raft multiplier and tweaks documentation.

command/agent/config.go

@@ -942,6 +942,11 @@ func DecodeConfig(r io.Reader) (*Config, error) {
 		result.AdvertiseAddrs.RPC = addr
 	}
 
+	// Enforce the max Raft multiplier.
+	if result.Performance.RaftMultiplier > consul.MaxRaftMultiplier {
+		return nil, fmt.Errorf("Performance.RaftMultiplier must be <= %d", consul.MaxRaftMultiplier)
+	}
+
 	return &result, nil
 }
 

command/agent/config_test.go

@@ -966,6 +966,12 @@ func TestDecodeConfig_Performance(t *testing.T) {
 	if config.Performance.RaftMultiplier != 3 {
 		t.Fatalf("bad: multiplier isn't set: %#v", config)
 	}
+
+	input = `{"performance": { "raft_multiplier": 11 }}`
+	config, err = DecodeConfig(bytes.NewReader([]byte(input)))
+	if err == nil || !strings.Contains(err.Error(), "Performance.RaftMultiplier must be <=") {
+		t.Fatalf("bad: %v", err)
+	}
 }
 
 func TestDecodeConfig_Services(t *testing.T) {

consul/config.go

@@ -18,9 +18,14 @@ const (
 	DefaultLANSerfPort = 8301
 	DefaultWANSerfPort = 8302
 
-	// See docs/guides/performance.html for information on how this value
-	// was obtained.
+	// DefaultRaftMultiplier is used as a baseline Raft configuration that
+	// will be reliable on a very basic server. See docs/guides/performance.html
+	// for information on how this value was obtained.
 	DefaultRaftMultiplier uint = 5
+
+	// MaxRaftMultiplier is a fairly arbitrary upper bound that limits the
+	// amount of performance detuning that's possible.
+	MaxRaftMultiplier uint = 10
 )
 
 var (

website/source/docs/agent/options.html.markdown

@@ -581,18 +581,19 @@ Consul will not enable TLS for the HTTP API unless the `https` port has been ass
   Consul. See the [Server Performance](/docs/guides/performance.html) guide for more details. The
   following parameters are available:
     * <a name="raft_multiplier"></a><a href="#raft_multiplier">`raft_multiplier`</a> - An integer
-      multiplier used by Consul servers to scale key Raft timing parameters. Tuning this affects
-      the time it takes Consul to detect leader failures and to perform leader elections, at the
-      expense of requiring more network and CPU resources for better performance.<br><br>A value
-      of 0, the default, means that Consul will use a lower-performance timing that's suitable for
-      [minimal Consul servers](/docs/guides/performance.html#minumum), currently equivalent to
-      setting this to a value of 5 (this default may be changed in future versions of Consul,
-      depending if the target minimum server profile changes). Above 0, higher values imply lower
-      levels of performance. Setting this to a value of 1 will configure Raft to its
-      highest-performance mode, equivalent to the default timing of Consul prior to 0.7, and is
-      recommended for [production Consul servers](/docs/guides/performance.html#production). See
-      the note on [last contact](/docs/guides/performance.html#last-contact) timing for more
-      details on tuning this parameter.
+      multiplier used by Consul servers to scale key Raft timing parameters. Omitting this value
+      or setting it to 0 uses default timing described below. Lower values are used to tighten
+      timing and increase sensitivity while higher values relax timings and reduce sensitivity.
+      Tuning this affects the time it takes Consul to detect leader failures and to perform
+      leader elections, at the expense of requiring more network and CPU resources for better
+      performance.<br><br>By default, Consul will use a lower-performance timing that's suitable
+      for [minimal Consul servers](/docs/guides/performance.html#minumum), currently equivalent
+      to setting this to a value of 5 (this default may be changed in future versions of Consul,
+      depending if the target minimum server profile changes). Setting this to a value of 1 will
+      configure Raft to its highest-performance mode, equivalent to the default timing of Consul
+      prior to 0.7, and is recommended for [production Consul servers](/docs/guides/performance.html#production).
+      See the note on [last contact](/docs/guides/performance.html#last-contact) timing for more
+      details on tuning this parameter. The maximum allowed value is 10.
 
 * <a name="ports"></a><a href="#ports">`ports`</a> This is a nested object that allows setting
   the bind ports for the following keys: