Autodetect the default network interface

Closes #13

Author: linkvt

README.md

@@ -77,7 +77,7 @@ Environment variables defaults are set in **image/environment/default.yaml**
 See how to [set your own environment variables](#set-your-own-environment-variables)
 
 
-- **KEEPALIVED_INTERFACE**: Keepalived network interface. Defaults to `eth0`
+- **KEEPALIVED_INTERFACE**: Keepalived network interface. Autodetected to interface with default route (see `ip route`)
 - **KEEPALIVED_PASSWORD**: Keepalived password. Defaults to `d0cker`
 - **KEEPALIVED_PRIORITY** Keepalived node priority. Defaults to `150`
 - **KEEPALIVED_ROUTER_ID** Keepalived virtual router ID. Defaults to `51`

image/environment/default.yaml

@@ -1,6 +1,8 @@
 KEEPALIVED_COMMAND_LINE_ARGUMENTS: --log-detail --dump-conf
 
-KEEPALIVED_INTERFACE: eth0
+# set the interface here to disable the default interface auto detection
+# KEEPALIVED_INTERFACE: eth0
+
 KEEPALIVED_PASSWORD: d0cker
 
 # For electing MASTER, highest priority wins.

image/service/keepalived/startup.sh

@@ -8,6 +8,17 @@ FIRST_START_DONE="${CONTAINER_STATE_DIR}/docker-keepalived-first-start-done"
 # container first start
 if [ ! -e "$FIRST_START_DONE" ]; then
 
+  # autodetect the default network interface
+  if [ -z "$KEEPALIVED_INTERFACE" ]; then
+    KEEPALIVED_INTERFACE=$(ip route | awk '/default/ { print $5 }')
+    if [ -z "$KEEPALIVED_INTERFACE" ]; then
+      echo "ERROR: Couldn't autodetect the default network interface, specify it manually."
+      exit 1
+    else
+      echo "Autodetected default network interface: $KEEPALIVED_INTERFACE"
+    fi
+  fi
+
   #
   # bootstrap config
   #