agent: Support protocol version setting

command/agent/agent.go

@@ -165,6 +165,9 @@ func (a *Agent) consulConfig() *consul.Config {
 	if a.config.Bootstrap {
 		base.Bootstrap = true
 	}
+	if a.config.Protocol > 0 {
+		base.ProtocolVersion = uint8(a.config.Protocol)
+	}
 
 	// Setup the ServerUp callback
 	base.ServerUp = a.state.ConsulServerUp

command/agent/command.go

@@ -61,6 +61,7 @@ func (c *Command) readConfig() *Config {
 	cmdFlags.BoolVar(&cmdConfig.Server, "server", false, "run agent as server")
 	cmdFlags.BoolVar(&cmdConfig.Bootstrap, "bootstrap", false, "enable server bootstrap mode")
 	cmdFlags.StringVar(&cmdConfig.StatsiteAddr, "statsite", "", "address of statsite instance")
+	cmdFlags.IntVar(&cmdConfig.Protocol, "protocol", -1, "protocol version")
 	if err := cmdFlags.Parse(c.args); err != nil {
 		return nil
 	}

command/agent/config.go

@@ -97,6 +97,9 @@ type Config struct {
 	// metrics will be streamed to that instance.
 	StatsiteAddr string `mapstructure:"statsite_addr"`
 
+	// Protocol is the Consul protocol version to use.
+	Protocol int `mapstructure:"protocol"`
+
 	// Checks holds the provided check definitions
 	Checks []*CheckDefinition `mapstructure:"-"`
 
@@ -122,6 +125,7 @@ func DefaultConfig() *Config {
 		SerfLanPort: consul.DefaultLANSerfPort,
 		SerfWanPort: consul.DefaultWANSerfPort,
 		Server:      false,
+		Protocol:    consul.ProtocolVersionMax,
 	}
 }
 
@@ -284,6 +288,9 @@ func MergeConfig(a, b *Config) *Config {
 	if b.LogLevel != "" {
 		result.LogLevel = b.LogLevel
 	}
+	if b.Protocol > 0 {
+		result.Protocol = b.Protocol
+	}
 	if b.NodeName != "" {
 		result.NodeName = b.NodeName
 	}

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

@@ -118,6 +118,10 @@ The options below are all specified on the command-line.
   various telemetry information to that instance for aggregation. This can be used to capture various
   runtime information.
 
+* `-protocol` - The Consul protocol version to use. This defaults to the latest
+  version. This should be set only when [upgrading](/docs/upgrading.html).
+  You can view the protocol versions supported by Consul by running `serf -v`.
+
 ## Configuration Files
 
 In addition to the command-line options, configuration can be put into

website/source/docs/compatibility.html.markdown

@@ -34,7 +34,7 @@ upgrading, see the [upgrading page](/docs/upgrading.html).
 </tr>
 <tr>
 <td>0.1</td>
-<td>0</td>
+<td>1</td>
 </tr>
 </table>
 

website/source/docs/upgrading.html.markdown

@@ -22,13 +22,13 @@ below, assume you're running version A of Consul, and then version B comes out.
 
 2. Shut down version A, and start version B with the `-protocol=PREVIOUS`
    flag, where "PREVIOUS" is the protocol version of version A (which can
-   be discovered by running `consul -v` or `consul members -detailed`).
+   be discovered by running `consul -v` or `consul members`).
 
 3. Once all nodes are running version B, go through every node and restart
    the version B agent _without_ the `-protocol` flag.
 
 4. Done! You're now running the latest Consul agent speaking the latest protocol.
-   You can verify this is the case by running `consul members -detailed` to
+   You can verify this is the case by running `consul members` to
    make sure all members are speaking the same, latest protocol version.
 
 The key to making this work is the [protocol compatibility](/docs/compatibility.html)
@@ -46,7 +46,7 @@ running `consul -v`. You'll see output similar to that below:
 ```
 $ consul -v
 Consul v0.1.0
-Agent Protocol: 1 (Understands back to: 0)
+Consul Protocol: 1 (Understands back to: 1)
 ```
 
 This says the version of Consul as well as the latest protocol version (1,