on_verify_batman

#!/bin/bash
# https://forum.freifunk.net/t/bessere-verteilung-von-knoten-clients-auf-sn-unter-fastd/12445

# peer limit may be used as a failsafe and not be changed.
# use this script as fastd on_verify to roughly balance peers. 
# If you feel that management should be even stricter and cause 
# fastd-peers to re-connect to other gateways, then also use the 
# cron-script that is adjusting the peer limit. This may be useful after 
# an outage.
#
# Managing client count per gateway would be a lot nicer, but the
# client count for the whole network can only be obtained by querying 
# other infrastructure (map/api).
#
# please append to your fastd.conf (config file of fastd) like following example
# "// " prefix is key!
#
# // minpeers 50
# // bufferpercentage 10
# // batctl /usr/local/sbin/batctl
#
set -ix
# things to adjust to your server
fastdsockets=( "/var/run/fastd-mesh-vpn-1280.sock" "/var/run/fastd-mesh-vpn-1312.sock" "/var/run/fastd-mesh-vpn-1426.sock" )
fastdconf="/etc/fastd/mesh-vpn-*/fastd.conf"
FASTD_PEERCONNECTIONS=2
BATCTL="/usr/sbin/batctl"
MINPEERS=50
BUFFERPERCENTAGE=10
DISABLEFILE=/root/disable

# this file may be created manually to allow for maintenance
[ -f $DISABLEFILE ] && exit 1

# check if batctl is avail
# otherwise we could try to read from proc sys directly
# this script should not do harm if it is broken => successful exit, 
# fastd will accept the peer.
[ -x $BATCTL ] || exit 0


# estimate network size and amount of gateways
net_peer_amount=$(($($BATCTL o |wc -l) * $FASTD_PEERCONNECTIONS))
gwamount=$($BATCTL gwl -H |wc -l)
((gwamount+=1))

## dirty count fastdconnections, 
## timeout means that connection on verify need 0.2 seconds, some consider this long!
# 0.2 seconds per verify means there can 50 connections be verified per second. 
connected_peer_amount=0
for fastdsocket in ${fastdsockets[@]}
do
  connectd_peer_thisinstance=$(timeout --foreground .2 ncat -U  $fastdsocket |grep -o established|wc -l )
  ((connected_peer_amount+=$connectd_peer_thisinstance))
done

# set connection limit and doing so, consider a buffersize
connection_average_estimate=$(( net_peer_amount / gwamount )) 
connection_limit_estimate=$((connection_average_estimate + (connection_limit_estimate * BUFFERPERCENTAGE)/100))

[[ $connection_limit_estimate -lt $MINPEERS ]] && connection_limit_estimate=$MINPEERS

# get actual peer limit
peerlimit=$(grep -oP '(?<=^peer\slimit\s)[0-9]+(?=\s*;$)' $fastdconf|awk -F: '{sum=sum+$2} END {print sum}')

[[ $peerlimit != *[!0-9]* ]] ||
{
    # set a sane default if peerlimit is not defined or not numeric
    peerlimit=$((connection_limit_estimate+1))
}

[[ $peerlimit -gt $connection_limit_estimate ]] ||
{
  # if a peer limit has been set via fastd.conf, cap the connection limit
  # estimate at that peer limit.
  connection_limit_estimate=$peerlimit
}

[[ $connection_limit_estimate -gt $connected_peer_amount ]] && exit 0

exit 1