GKE node-pool pod IP CIDR range usage calc script

gke-np-ip-utilization.rb

#!/usr/bin/env ruby
#
# Show GKE per-node-pool pod IP CIDR range utilization.
#
# Usage:
#  gcloud container clusters describe <cluster-name> --location <loc> --format=json | ./gke-np-ip-utilization.rb

require 'json'
require 'ipaddr'

data = JSON.parse(ARGF.read)

def total_ips_in_range(cidr)
  IPAddr.new(cidr).to_range.count
end

header_fmt = "%-30s %-16s %-11s %-15s %-6s %-14s\n"
row_fmt =    "%-30s %-16s /%-10d %-15s %-6.0f %-14d\n"

printf(header_fmt, 'nodePool', 'podCidrBlock', 'podCidrSize', 'maxPods/Node', '%-util', 'remainingNodes')
puts '-' * 97

data['nodePools'].each do |node_pool|
  name = node_pool['name']
  utilization = node_pool['networkConfig']['podIpv4RangeUtilization'] * 100

  cidr_block = node_pool['networkConfig']['podIpv4CidrBlock']
  cidr_size = node_pool['podIpv4CidrSize'].to_i
  total_ips = total_ips_in_range(cidr_block)
  ips_per_node = total_ips_in_range("0.0.0.0/#{cidr_size}")
  max_pods_per_node = node_pool['maxPodsConstraint']['maxPodsPerNode']

  available_ips = total_ips - (total_ips * node_pool['networkConfig']['podIpv4RangeUtilization'])
  num_nodes = (available_ips / ips_per_node).floor

  printf(row_fmt, name, cidr_block, cidr_size, max_pods_per_node, utilization, num_nodes)
end