#!/usr/bin/env python3
# "Have-A-Port" | ephemeral port picker for LoadBalancer-type Kubernetes services in clusters with a single-address external address pool
from kubernetes import client, config
import sys, random

SVC_TYPE = 'LoadBalancer'

def getopts():
        """parse command-line"""
        from optparse import OptionParser, OptionValueError
        usage = "%prog [options]"
        parser = OptionParser(usage=usage)
        parser.add_option("-n", "--count", type="int", default=1, dest="port_count", help="number of ports needed (default: %default)")
        return parser.parse_args()

options, args = getopts()

# load client configuration (kubeconfig)
config.load_kube_config()

# establish API connection
connection = client.CoreV1Api()
# query service objects
all_services = connection.list_service_for_all_namespaces(watch=False)

# determine ports in use
ports_per_svc = [ svc.spec.ports for svc in all_services.items if svc.spec.type == SVC_TYPE]
used_ports = [svc_port.port for svc_ports in ports_per_svc for svc_port in svc_ports]

# determine available ports
full_port_range = range(49152, 65536) # https://tools.ietf.org/html/rfc6335#section-8.1.2
available_ports = list(set(full_port_range) - set(used_ports))

# pick available ports
print(' '.join(map(str, random.sample(available_ports, options.port_count))))