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esarver/CLIENT-ip_updater_node.service

Last active May 2, 2017 12:28
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Socket-based IP Updater
Raw
README-IP-Updater.md

Install code on respective boxes. On the server, install in /opt/ip-updater/. On the client install in /opt/ip-updater-node. Remove CLIENT- or SERVER- from the filenames.

Make sure that the IP addresses, host names, and file paths are all filled in. Don't forget to make the *.sh files executable.

Copy the *.service and *.socket files into /etc/systemd/system/ and run systemctl daemon-reload and systemctl enable ip_updater... on all of your boxes. Note: Symlinks will not work

These services should be available upon reboot.

Note: The machine with a static IP must be the server and must be fully running before the clients boot to make sure the message makes it to the hosts file of the server with the static IP.

Raw
CLIENT-ip_updater_node.service
[Unit]
Description=Client Side of the IP Updater
After=network-online.target
[Service]
Type=oneshot
ExecStart=/opt/ip-updater-node/ip_updater_node.sh
[Install]
WantedBy=multi-user.target
Raw
CLIENT-ip_updater_node.sh
#!/bin/bash
echo "<ENTER HOST NAME HERE>" | nc <ENTER NAME/IP ADDRESS OF COMPUTER WITH STATIC IP HERE> 9999
Raw
SERVER-ip_updater.py
#!/usr/bin/python
#modified from https://gist.github.com/drmalex07/333d8a88c4918954e8e4
from SocketServer import TCPServer, StreamRequestHandler
import socket
import logging
import subprocess
class Handler(StreamRequestHandler):
def handle(self):
self.data = self.rfile.readline().strip()
logging.info("From <%s>: %s" % (self.client_address, self.data))
subprocess.call(["/opt/ip-updater/ip_updater.sh", self.data, self.client_address[0]])
class Server(TCPServer):
SYSTEMD_FIRST_SOCKET_FD = 3
def __init__(self, server_address, handler_cls):
# Invoke base but omit bind/listen steps (performed by systemd activation)
TCPServer.__init__(
self, server_address, handler_cls, bind_and_activate=False)
# Override Socket
self.socket = socket.fromfd(
self.SYSTEMD_FIRST_SOCKET_FD, self.address_family, self.socket_type)
if __name__ == "__main__":
logging.basicConfig(level=logging.INFO)
HOST, PORT = "localhost", 9999 # not really needed here
server = Server((HOST, PORT), Handler)
server.serve_forever()
Raw
SERVER-ip_updater.service
[Unit]
Description=IP Updater
After=network-online.target ip_updater.socket
Requires=ip_updater.socket
[Service]
Type=simple
ExecStart=/opt/ip-updater/ip_updater.py
TimeoutStopSec=5
[Install]
WantedBy=multi-user.target
Raw
SERVER-ip_updater.sh
#!/bin/bash
hostsfile=<ENTER LOCATION OF HOSTS FILE HERE>
logfile=/opt/ip-updater/ip_updater.log
echo "-------------------------" >> $logfile
echo "\"$line\""
read -ra arr <<<"$1"
hostname=${arr[0]}
ipaddr=${arr[1]}
echo "Hostname: \"$hostname\"" >> $logfile
echo "IP Addr: \"$ipaddr\"" >> $logfile
if grep -q $hostname "$hostsfile"; then
echo "It's in $hostsfile." >> $logfile
echo "Updating $hostsfile..." >> $logfile
sed -r "s/^ *[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+( +$hostname)/$ipaddr\1/" -i "$hostsfile"
echo "Updated $hostsfile!" >> $logfile
else
echo "It's not in $hostsfile." >> $logfile
echo "Adding to $hostsfile..." >> $logfile
echo "$ipaddr $hostname" >> $hostsfile
echo "Added to $hostsfile." >> $logfile
fi
echo "Exiting IP Updater." >> $logfile
Raw
SERVER-ip_updater.socket
[Unit]
Description=IP Updater Socket
PartOf=ip_updater.service
[Socket]
ListenStream=9999
[Install]
WantedBy=sockets.target
@esarver
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esarver commented May 1, 2017

The Client version doesn't seem to be working on computer startup, for some reason. Any suggestions anybody? I'm working on debugging...

@pelgerr
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pelgerr commented May 1, 2017 •
edited
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In the client service try using network-online.target. This essentially waits to run your service until all of the automatic connections either succeed, fail or time out. You might also want to use the Wants directive. This maybe isn't totally necessary but if for whatever reason something goes wonky you can use this to make sure that the network-online.target unit is started before your own unit activates.

So if you do something like this:

[Unit]
Description=Client Side of the IP Updater
Wants=network-online.target
After=network.target network-online.target

you are making sure your dependency units are run first and your own unit isn't run until they are completed.

Edit: Wants is similar to Requires, just less strict. It will attempt to run the listed units but if they fail or are missing, the current unit will continue to run.

Edit 2: I should clarify that this may not fix the issue. These are just changes that could be a good idea to make.

@esarver
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esarver commented May 2, 2017 •
edited
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I updated it with some changes that I made. I think that should set it up for success (it works on my machines) so give it a try and let me know if it works for you!

Things I'd still like to do to improve this software:

  • Put the hostname of the client and server boxes in a separate text file for easy deployment
  • Simplify server code to one file (not the systemd stuff, but add the modification of the /etc/hosts files to the python script)
  • Write easy installer script to simplify installation/deployment instructions

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