Do not modify configuration files

The hook was looking for the default gateway in the machine's configuration
files, but this didn't work when using DHCP. Also, there is no real advantage
in modifying the machine's configuration files.

So we just change the routes at run time.

hooks/install

@@ -2,7 +2,6 @@
 # Here do anything needed to install the service
 # e.g. apt install -y foo
 # Make sure this hook exits cleanly and is idempotent.
-set -e
 set -x
 status-set maintenance "Setting the default gateway"
 
@@ -21,58 +20,23 @@ source /etc/lsb-release
 RELEASE_MAJOR="$(echo $DISTRIB_RELEASE | awk -F '.' '{print $1}')"
 
 if [ "$RELEASE_MAJOR" -le "16" ]; then
-    OLD_GATEWAY_IP=`grep -s gateway /etc/network/interfaces /etc/network/interfaces.d/*.cfg | head -1 | awk '{print $NF}'`
-
-    if [ "$GATEWAY_IP" == "$OLD_GATEWAY_IP" ]; then
-        juju-log "Default gateway is already set. Exiting..."
-        status-set active "Unit is ready."
-        exit 0
-    fi
-
-    apt install -y sipcalc
-
-    GATEWAY_NET=`sipcalc $GATEWAY | grep "Network address" | awk '{print $NF}'`
-
-    IFS=$'\n'
-    FOUND=0
-    for LINE in $(grep -s address /etc/network/interfaces /etc/network/interfaces.d/*.cfg); 
-    do
-        FILE=`echo $LINE | awk '{print substr($1, 0, length($1)-1)}'`  # drop ':'
-        ADDRESS=`echo $LINE | awk '{print $NF}'`
-        ADDRESS_NET=`sipcalc $ADDRESS | grep "Network address" | awk '{print $NF}'`
-        if [ "$ADDRESS_NET" == "$GATEWAY_NET" ]; then
-            FOUND=1
-        fi
-    done
-    unset IFS
-
-    if [ "$FOUND" -gt 0 ]; then
-        juju-log "Setting default gateway: $GATEWAY_IP ..."
-        sed -i "/${GATEWAY_IP}/a\    gateway $GATEWAY_IP" $FILE
-        if [ ! -z "$OLD_GATEWAY_IP" ]; then
-            juju-log "Removing old default gateway $OLD_GATEWAY_IP..."
-            sed -i "/${OLD_GATEWAY_IP}/d" $FILE
-        fi
-        ip -force route del default || true
-        ip route add default via $GATEWAY_IP
-        juju-log "Default gateway changed"
-        status-set active "Unit is ready"
-    else
-        juju-log "Network not found. Exiting..."
-        status-set blocked "Incorrect gateway IP."
-    fi
+    # copy metric 0 routes to routes with metric 1
+    ip route show | grep "^default" | grep -v metric | while read line; do ip route append $line metric 1 || true; done
+    # delete metric 0 routes
+    ip route show | grep "^default" | grep -v metric | while read line; do ip route del $line metric 0; done
 else # release is not less or equal than trusty
     # copy metric 0 routes to routes with metric 1
     ip route show default metric 0 | while read line; do ip route append $line metric 1 || true; done
     # delete metric 0 routes
     ip route show default metric 0 | while read line; do ip route del $line metric 0; done
-    # add our route
-    if ip route replace default via $GATEWAY_IP metric 0; then
-        juju-log "Default gateway set"
-        status-set active "Unit is ready"
-    else
-        juju-log "Route change failed. Exiting..."
-        status-set blocked "Incorrect gateway IP."
-    fi
+fi
+
+# add our route
+if ip route replace default via $GATEWAY_IP metric 0; then
+    juju-log "Default gateway set"
+    status-set active "Unit is ready"
+else
+    juju-log "Route change failed. Exiting..."
+    status-set blocked "Incorrect gateway IP."
 fi