(untested) allow flannel interface selection, clarified for vagrant

users.

group_vars/all.yml

@@ -15,7 +15,13 @@ kube_service_addresses: 10.254.0.0/16
 kube_overlay_ip: 4.0.0.0
 # Prefix length of kube_overlay_ip range.
 kube_overlay_prefix: 16
-
+# Flannel registers an interface with etcd
+# and this interface gets a unique subnet for all its docker containers.
+# Thus, the value you use here needs to be unique on ALL nodes of your cluster.
+# In vagrant setups, this often is eth1 (eth0 is the bridge sometimes). 
+# HINT: If your nodes are spinning up containers w/ the same IP subnet,
+# then you messed it up !
+flannel_iface: eth0
 
 # Internal DNS configuration.
 # Kubernetes can create and mainatain its own DNS server to resolve service names

roles/flannel/templates/flanneld.j2

@@ -8,5 +8,7 @@ FLANNEL_ETCD="http://{{ groups['etcd'][0] }}:4001"
 FLANNEL_ETCD_KEY="/coreos.com/network"
 
 # Any additional options that you want to pass
-#FLANNEL_OPTIONS=""
-
+# In this case, we give it an interface, especially important 
+# for cases such as vagrant, where eth0 might be a bridge, and you 
+# want to use eth1.
+FLANNEL_OPTIONS="--iface={{ flannel_iface }}"