#!/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'
PORT_COUNT = 1

if len(sys.argv) > 1:
    try:
        PORT_COUNT = int(sys.argv[-1])
    except:
        sys.exit('optional positional parameter must be a number (default: 1)')

# 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, PORT_COUNT))))