docker-swarm iptables FORWARD custom chain enforcement

custom-chain-enforcement.service

[Unit]                                                                          
Description=Public filter enforcement Service                                   
                                                                                
[Service]                                                                       
Type=simple                                                                     
ExecStart=/home/user/custom-chain-enforcement.sh                            
KillMode=mixed                                                                  
                                                                                
TimeoutStartSec=0                                                               
RestartSec=0                                                                    
                                                                                
Restart=always                                                                  
                                                                                
[Install]                                                                       
WantedBy=multi-user.target                                                      
Alias=public-filter.service

custom-chain-enforcement.sh

#!/bin/bash                                                                     
                                                                                
CUSTOM_CHAIN=PUBLIC_FILTER                                                      
DELAY=10                                                                        
                                                                                
while [ True ];                                                                 
do                                                                              
                                                                                
  custom_chain_position=`iptables-save | grep -e "-A FORWARD" | grep --line-number -e "-A FORWARD -j ${CUSTOM_CHAIN}" | sed 's/\([0-9]\+\):.*/\1/g'`
                                                                                
  if [[ -z "$custom_chain_position" ]]                                          
  then                                                                          
    echo "`date`: Insert custom chain."                                         
    iptables -I FORWARD -j ${CUSTOM_CHAIN}                                      
  elif [[ "$custom_chain_position" -ne "1" ]]                                   
  then                                                                          
    echo "`date`: Enforce the priority of custom chain."                        
    iptables -D FORWARD ${custom_chain_position}                                
    iptables -I FORWARD -j ${CUSTOM_CHAIN}                                      
  fi                                                                            
                                                                                
  sleep $DELAY                                                                  
                                                                                
done