Fingerprint: config parameter for interface and native method for IP address

client/config/config.go

@@ -31,6 +31,9 @@ type Config struct {
 	// Region is the clients region
 	Region string
 
+	// Network interface to be used in network fingerprinting
+	NetworkInterface string
+
 	// Servers is a list of known server addresses. These are as "host:port"
 	Servers []string
 

client/fingerprint/network_unix.go

@@ -3,6 +3,7 @@
 package fingerprint
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -38,10 +39,14 @@ func (f *NetworkFingerprint) Fingerprint(cfg *config.Config, node *structs.Node)
 	if "darwin" == runtime.GOOS {
 		defaultDevice = "en0"
 	}
+	// User-defined override for the default interface
+	if cfg.NetworkInterface != "" {
+		defaultDevice = cfg.NetworkInterface
+	}
 
 	newNetwork.Device = defaultDevice
 
-	if ip := f.ifConfig(defaultDevice); ip != "" {
+	if ip := f.ipAddress(defaultDevice); ip != "" {
 		node.Attributes["network.ip-address"] = ip
 		newNetwork.IP = ip
 		newNetwork.CIDR = newNetwork.IP + "/32"
@@ -129,6 +134,56 @@ func (f *NetworkFingerprint) linkSpeedEthtool(path, device string) int {
 	return mbs
 }
 
+// ipAddress returns the first IPv4 address on the configured default interface
+// Tries Golang native functions and falls back onto ifconfig
+func (f *NetworkFingerprint) ipAddress(device string) string {
+	if ip, err := f.nativeIpAddress(device); err == nil {
+		return ip
+	}
+
+	return f.ifConfig(device)
+}
+
+func (f *NetworkFingerprint) nativeIpAddress(device string) (string, error) {
+	// Find IP address on configured interface
+	var ip string
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return "", errors.New("could not retrieve interface list")
+	}
+
+	// TODO: should we handle IPv6 here? How do we determine precedence?
+	for _, i := range ifaces {
+		if i.Name != device {
+			continue
+		}
+
+		addrs, err := i.Addrs()
+		if err != nil {
+			return "", errors.New("could not retrieve interface IP addresses")
+		}
+
+		for _, a := range addrs {
+			switch v := a.(type) {
+			case *net.IPNet:
+				if v.IP.To4() != nil {
+					ip = v.IP.String()
+				}
+			case *net.IPAddr:
+				if v.IP.To4() != nil {
+					ip = v.IP.String()
+				}
+			}
+		}
+	}
+
+	if net.ParseIP(ip) == nil {
+		return "", errors.New(fmt.Sprintf("could not parse IP address `%s`", ip))
+	}
+
+	return ip, nil
+}
+
 // ifConfig returns the IP Address for this node according to ifConfig, for the
 // specified device.
 func (f *NetworkFingerprint) ifConfig(device string) string {

command/agent/agent.go

@@ -192,6 +192,9 @@ func (a *Agent) setupClient() error {
 		conf.AllocDir = a.config.Client.AllocDir
 	}
 	conf.Servers = a.config.Client.Servers
+	if a.config.Client.NetworkInterface != "" {
+		conf.NetworkInterface = a.config.Client.NetworkInterface
+	}
 
 	// Setup the node
 	conf.Node = new(structs.Node)

command/agent/config.go

@@ -139,6 +139,9 @@ type ClientConfig struct {
 
 	// Metadata associated with the node
 	Meta map[string]string `hcl:"meta"`
+
+	// Interface to use for network fingerprinting
+	NetworkInterface string `hcl:"network_interface"`
 }
 
 // ServerConfig is configuration specific to the server mode
@@ -384,6 +387,9 @@ func (a *ClientConfig) Merge(b *ClientConfig) *ClientConfig {
 	if b.NodeClass != "" {
 		result.NodeClass = b.NodeClass
 	}
+	if b.NetworkInterface != "" {
+		result.NetworkInterface = b.NetworkInterface
+	}
 
 	// Add the servers
 	result.Servers = append(result.Servers, b.Servers...)

website/source/docs/agent/config.html.md

@@ -84,7 +84,7 @@ nodes, unless otherwise specified:
     TCP and UDP should be routable between the server nodes on this port.
     Defaults to `4648`. Only used on server nodes.
 
-* <a id="addresses">`addresses`</a>: Controls the bind address for individual 
+* <a id="addresses">`addresses`</a>: Controls the bind address for individual
   network services. Any values configured in this block take precedence over the
   default [bind_addr](#bind_addr). The value is a map of IP addresses and
   supports the following keys:
@@ -154,7 +154,7 @@ configured on client nodes.
   * `enabled`: A boolean indicating if server mode should be enabled for the
     local agent. All other server options depend on this value being set.
     Defaults to `false`.
-  * <a id="bootstrap_expect">`bootstrap_expect`</a>: This is an integer 
+  * <a id="bootstrap_expect">`bootstrap_expect`</a>: This is an integer
     representing the number of server nodes to wait for before bootstrapping. It
     is most common to use the odd-numbered integers `3` or `5` for this value,
     depending on the cluster size. A value of `1` does not provide any fault
@@ -205,8 +205,10 @@ configured on server nodes.
   * <a id="node_class">`node_class`</a>: A string used to logically group client
     nodes by class. This can be used during job placement as a filter. This
     option is not required and has no default.
-  * <a id="meta">`meta`</a>: This is a key/value mapping of metadata pairs. This 
+  * <a id="meta">`meta`</a>: This is a key/value mapping of metadata pairs. This
     is a free-form map and can contain any string values.
+  * `network_interface`: This is a string to force network fingerprinting to use
+    a specific network interface
 
 ## Atlas Options