set mtu in cni spec to auto configure MTU's of the pod's veth's and…

… kube-bridge interfaces

Fixes #165

pkg/controllers/routing/network_routes_controller.go

@@ -2,6 +2,7 @@ package routing
 
 import (
 	"context"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io/ioutil"
@@ -341,6 +342,46 @@ func (nrc *NetworkRoutingController) updateCNIConfig() {
 			glog.Fatalf("Failed to insert `subnet`(pod CIDR) into CNI conf file: %s", err.Error())
 		}
 	}
+
+	err = nrc.autoConfigureMTU()
+	if err != nil {
+		glog.Fatalf("Failed to auto-configure MTU: %s", err.Error())
+	}
+}
+
+func (nrc *NetworkRoutingController) autoConfigureMTU() error {
+	mtu, err := getMTUFromNodeIP(nrc.nodeIP)
+	file, err := ioutil.ReadFile(nrc.cniConfFile)
+	if err != nil {
+		return fmt.Errorf("Failed to load CNI conf file: %s", err.Error())
+	}
+	var config interface{}
+	err = json.Unmarshal(file, &config)
+	if err != nil {
+		return fmt.Errorf("Failed to parse JSON from CNI conf file: %s", err.Error())
+	}
+	if strings.HasSuffix(nrc.cniConfFile, ".conflist") {
+		configMap := config.(map[string]interface{})
+		for key := range configMap {
+			if key != "plugins" {
+				continue
+			}
+			pluginConfigs := configMap["plugins"].([]interface{})
+			for _, pluginConfig := range pluginConfigs {
+				pluginConfigMap := pluginConfig.(map[string]interface{})
+				pluginConfigMap["mtu"] = mtu
+			}
+		}
+	} else {
+		pluginConfig := config.(map[string]interface{})
+		pluginConfig["mtu"] = mtu
+	}
+	configJSON, _ := json.Marshal(config)
+	err = ioutil.WriteFile(nrc.cniConfFile, configJSON, 0644)
+	if err != nil {
+		return fmt.Errorf("Failed to insert `mtu` into CNI conf file: %s", err.Error())
+	}
+	return nil
 }
 
 func (nrc *NetworkRoutingController) watchBgpUpdates() {

pkg/controllers/routing/utils.go

@@ -120,6 +120,26 @@ func getNodeSubnet(nodeIP net.IP) (net.IPNet, string, error) {
 	return net.IPNet{}, "", errors.New("Failed to find interface with specified node ip")
 }
 
+func getMTUFromNodeIP(nodeIP net.IP) (int, error) {
+	links, err := netlink.LinkList()
+	if err != nil {
+		return 0, errors.New("Failed to get list of links")
+	}
+	for _, link := range links {
+		addresses, err := netlink.AddrList(link, netlink.FAMILY_ALL)
+		if err != nil {
+			return 0, errors.New("Failed to get list of addr")
+		}
+		for _, addr := range addresses {
+			if addr.IPNet.IP.Equal(nodeIP) {
+				lintMTU := link.Attrs().MTU
+				return lintMTU - 20, nil // -20 to accommodate IPIP header
+			}
+		}
+	}
+	return 0, errors.New("Failed to find interface with specified node ip")
+}
+
 // generateTunnelName will generate a name for a tunnel interface given a node IP
 // for example, if the node IP is 10.0.0.1 the tunnel interface will be named tun-10001
 // Since linux restricts interface names to 15 characters, if length of a node IP