Implement action for rebalancing L3 agents in HA environment

[John Lettman]

After cycling all other partners on a neutron-gateway HA configuration, all L3 agents appear stuck on the remaining partner. This condition is undesirable as the HA becomes completely unbalanced.

It would be helpful to automatically detect/rectify this condition or offer an action to rebalance the L3 agents after maintenance activities.

Our current workaround is the following script (for a 2 gateway HA):

UNIT="neutron-gateway/0"
HOSTNAME=$(juju run -u $UNIT -- hostname)
L3AGENT=$(openstack network agent list --host $HOSTNAME --agent-type l3 -cID -fvalue)

HAROUTERS=($(openstack router list -cHA -cID -fvalue | awk '/True/ {print $1}' | tr '\n' ' '));

HALEN=${#HAROUTERS[@]};
HASEL=$(( HALEN / 2 ));

for (( i=0; i<${HASEL}; i++ )); do
        neutron l3-agent-router-remove $L3AGENT ${HAROUTERS[$i]};
done;

# wait a while here

for (( i=0; i<${HASEL}; i++ )); do
        neutron l3-agent-router-add $L3AGENT ${HAROUTERS[$i]};
done;