add-dns-server.sh

#!/bin/sh

DNS_SERVER=127.0.0.1

# Appends $DNS_SERVER to the DNS server list.
cat /etc/resolv.conf | awk '/^\s*nameserver\W/ { print $2 }' | xargs -J '%' sudo networksetup -setdnsservers 'Wi-Fi' '%' $DNS_SERVER

# Flushes DNS resolver caches.
sudo killall -HUP mDNSResponder

gcp.rb

#!/usr/local/bin/ruby

##
## Get host name and IP address pairs from GCP
##

GCP_APPS = %w(compute sql)

hosts = GCP_APPS.flat_map do |app|
  `gcloud #{app} instances list 2>&- | tail -n +2`.lines.map { |e|
    e.split(/\s+/).values_at(0, 3)
  }
end

##
## Setup zone records
##

ZoneRecord = Struct.new :name, :ttl, :record_class, :record_type, :data

records = []
records << ZoneRecord.new("@", "", "IN", "SOA", %q(local. root.local. (
  2002122001 ; Serial
  3600       ; Refresh
  900        ; Retry
  604800     ; Expire
  86400      ; Minimum
)))

LOCAL_IP_ADDR = "127.0.0.1"

records << ZoneRecord.new(   "", "", "IN", "NS",  "dns.local.")
records << ZoneRecord.new("dns", "", "IN",  "A", LOCAL_IP_ADDR)
records.concat(hosts.map { |name, ip_addr|
  ZoneRecord.new(name, "", "IN", "A", ip_addr)
})

##
## Output zone config
##

rows = records.map(&:to_a)
cols = (0...rows.map(&:size).max).map do |col|
  rows.map { |r| (r[col] || "").size }.max
end

puts "$TTL 86400"
rows.each do |r|
  puts r.zip(cols).map { |e, n| "%- #{n + 4}s" % e }.join("").rstrip
end