kube2haproxy.py

#!/usr/bin/python
#    Kubernetes to HA Proxy config updater script
#    Copyright (C) 2017  Glen Pitt-Pladdy
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
#
# See: https://www.pitt-pladdy.com/blog/_20170328-130720_0100_Kubernetes_to_learn_Part_4/
#


import json
import subprocess
import time
import sys
import os

template = '/etc/haproxy/haproxy.cfg.TEMPLATE'
outputcfg = '/etc/haproxy/haproxy.cfg'
polldelay = 5



def getnodes():
	p = subprocess.Popen ( ['kubectl','get','nodes','-o','json'], stdout=subprocess.PIPE, stderr=subprocess.PIPE )
	stdout,stderr = p.communicate()
	return json.loads ( stdout )

def getservices():
	p = subprocess.Popen ( ['kubectl','get','services','-o','json'], stdout=subprocess.PIPE, stderr=subprocess.PIPE )
	stdout,stderr = p.communicate()
	return json.loads ( stdout )

def reloadhaproxy():
	p = subprocess.Popen ( ['systemctl','reload','haproxy'], stdout=None, stderr=None )


lastconfig = ''
while True:
	# get all our nodes
	nodes = []
	for node in getnodes()['items']:
		for state in node['status']['conditions']:
			if state['type'] == 'Ready' and state['status'] == 'True':
				# good node - add this
				for address in node['status']['addresses']:
					if address['type'] == 'InternalIP':
						nodes.append ( address['address'] )
						break
				break
	# ingest all our services
	services = {}
	for service in getservices()['items']:
		if service['spec']['type'] == 'NodePort':
			app = service['spec']['selector']['app']
			if app not in services: services[app] = {}
			tier = service['spec']['selector']['tier']
			if 'tier' not in services: services[app][tier] = {}
			for portspec in service['spec']['ports']:
				if portspec['protocol'] != 'TCP': continue	# we can't do this
				services[app][tier][portspec['port']] = portspec['nodePort']

	# generate HA Proxy config snipped
	config = "\n# automatically generated by %s\n\n" % sys.argv[0]
	portused = {}
	for app in services:
		for tier in services[app]:
			for port in services[app][tier]:
				# frontend
				config += "frontend %s_%s\n" % (app,tier)
				listenport = int(port)
				while listenport in portused: listenport += 1
				portused[listenport] = True
				config += "\tbind *:%d\n" % listenport
				config += "\tdefault_backend %s_%s\n" % (app,tier)
				# backend
				config += "backend %s_%s\n" % (app,tier)
				config += "\tbalance roundrobin\n"
				for node in nodes:
					config += "\tserver %s %s:%s check\n" % (node.replace('.','_'),node,services[app][tier][port])

	if config != lastconfig:
		print
		print "Configuration Changed!"
		print config
		with open ( template, 'rt' ) as fi:
			with open ( outputcfg+'.TMP', 'wt' ) as fo:
				fo.write ( fi.read() )
				fo.write ( config )
			os.rename ( outputcfg+'.TMP', outputcfg )
			reloadhaproxy ()
		lastconfig = config


	time.sleep ( polldelay )