subnets_maths.py

#!/usr/bin/env python

"""
POC for subnet calculator
"""

import ipaddress
from math import (
    log,
    ceil
)

pow2_2_prefix = {

    '16': 28,
    '32': 27,
    '64': 26,
    '128': 25,
    '256': 24,
    '512': 23,
    '1024': 22,
    '2048': 21,
    '4096': 20,
    '8192': 19,
    '16384': 18,
    '32768': 17,
    '65536': 16,
    '131072': 15,
    '262144': 14,
    '524288': 13,
    '1048576': 12,
    '2097152': 11,
    '4194304': 10,
    '8388608': 9,
    '16777216': 8
}

clpow2 = lambda x: pow(2, int(log(x, 2) + 0.5))
nxtpow2 = lambda x: int(pow(2, ceil(log(x, 2))))

def cut_per_az(az_cidr, layers_cidr):
    """
    """

    maj_splits = list(az_cidr.subnets(prefixlen_diff=1))
    layers_cidr['app'].append(maj_splits[0])
    min_splits = list(maj_splits[1].subnets(prefixlen_diff=1))
    layers_cidr['pub'].append(min_splits[0])
    layers_cidr['stor'].append(min_splits[1])


def get_subnets(cidr, azs):
    """
    Main function
    """
    cidr = f'{cidr}'
    vpc_net = ipaddress.IPv4Network(cidr)
    number_ips = int(vpc_net.num_addresses - 2)

    if (azs != 2) and (azs % 2):
        azs += 1

    layers_cidr = {
        'app' : [],
        'pub': [],
        'stor': []
    }

    ips_per_az = number_ips / azs
    pow2 = clpow2(ips_per_az)
    azs_prefix = pow2_2_prefix['%d' % (pow2)]
    subnets_per_az = list(vpc_net.subnets(new_prefix=azs_prefix))

    for az in subnets_per_az:
        cut_per_az(az, layers_cidr)

    return layers_cidr


def get_subnet_layers(cidr, azs):
    """
    Returns Dictionary of the CIDRs per layer name
    """
    layers = get_subnets(cidr, azs)
    cidrs = {}

    for layer in layers:
        cidrs[layer] = []
        sub_list = []
        for subnet in layers[layer]:
            sub_list.append('%s' % (subnet))
        cidrs[layer] = sub_list
    return cidrs